Investigation of casing shoe depth determination taking into

consideration the Kick Tolerance and Well Integrity

An MS thesis

by

Alan Yaseen Othman

Submitted to the Petroleum and Natural Gas Institute of

University of Miskolc

in partial fulfillment of the requirements for the degree of

MASTER OF SCIENCE

in Petroleum Engineering

May 2014

I

Dedication

This thesis is dedicated to:

My Parents Father and Mother.

My wife and My Daughter (DEYA).

All my friends and Relatives.

My kind Teacher(Prof.AkramHamudiAbdulwahab Al-Hiti), in the University of Baghdad-

Faculty of engineering petroleum engineering Department, who was my Bachalor Thesis

adviser, when I graduated Drilling Engineer.

Ministry Of Natural Resources – Kurdistan Region Governmwnt-Erbil-Iraq.

II

Acknowledgements

I would like to thanks supervisorDr.ImreFedererAssocciateProfessor for his support and

guidance through outthewriting of the thesis.

I would like also to thank Dr.Tibor Szabo who is one of the drilling group in the department

of Petroleum and Natural Gas institute for his informations about the kick tolerance calculator

and cheaking some of data and results in my thesis.

I have special thanks for Prof.TurzoZoltan in the same department and

myfriendEng.MakokGhafoorDarwesh for their helpings me by some of

computer’sinformationsaboutthe structure of the thesis.

I am particularly grateful to the Kalegran oil company (a branch of MOL in Kurdistan), for

providing my scholarship and for a lot help to finish my MSc successfully.

Special thanks to the Ministry of Natural Resources in Erbil for giving me the opportunity of

study in Hungary in order to finish my MSc.

Real thanks for my father in low (Prof.Rafiq Mohamed Shwany), UniversiSaladdin-Erbil-

Iraq-Kurdistan for his helping me about the structure of the thesis and the reallity thanks for

my Uncles for theirs encouragement and moral support during my studies and working on this

thesis.

In addition I express my gratitude to everyone providing me with informations and help.

I hereby declare that this Master Thesis has been written by me and in accordance to the

FacultyOf earth science& Engineering- University of Miskolc.

III

Executive Summary

This thesis investigates of casing shoe depth determination taking into consideration the kick

tolerance and well integrity, summerizes short description of the study are;

Investigate the importance of kick tolerance and well integrity considering with safe well

planning.

Describe the theoretical back ground of kick tolerance than a key of element of casing shoe

depth determination.

Introduce the theoretical and practical methods that are usable to determine the formation

integrity.

Using a selected theoretical well data perform sensitive analyses to examine relationship

between kick tolerance and well integrity.

Determine for the given well safe casing shoe depth that is acceptable the required well

integrity.

IV

Table of Contents Dedication ............................................................................................................................................... I

Acknowledgements ............................................................................................................................... II

Executive Summary ............................................................................................................................ III

Introduction ........................................................................................................................................... 1

1 Theory of KICK Tolerance................................................................................................................ 3

1.1 Formation Integrity test ................................................................................................................. 3

1.2 Formation Integrity Test: Purpose ................................................................................................. 3

1.3 Fracturre Gradient Determination ................................................................................................. 4

1.4 Theory of wellbore breakage ........................................................................................................ 5

1.4.1 Hubbert and Willis Method .................................................................................................... 6

1.5 Formation Breakdown Gradient : .................................................................................................. 8

1.6 Effects of hole deviation on Formation Breakdown Gradient ....................................................... 9

1.7 Casing Seat Selection .................................................................................................................. 10

1.8 CasingSeatSelectionSteps ........................................................................................................... 11

1.9 Overburdenpressure ..................................................................................................................... 12

1.10 Casing Seat Selection based on methodology for design setting depth of surface and

intermidate casing stringin agaswell: ................................................................................................ 13

1.11 KickTolerance ........................................................................................................................... 15

1.11.1 Kick Tolerance when the top of the kick at the casing shoe .............................................. 16

1.12 Gas Influx: ideal gas law or standing – Katz Z factor ............................................................... 18

1.12.1 Gas influx idal gas low ....................................................................................................... 18

1.12.2 Gas influx the standing Ktz Z factor .................................................................................. 19

1.12.3 Calculation through the profile ........................................................................................... 20

1.12.4 True vertical depth for the shoe and the kick zone ........................................................... 20

1.12.5 Calculation the meassure length for the influx heights at the shoe and the kick zone ....... 22

1.13 Kick tolerance elements ............................................................................................................ 22

........................................................................................................................................................... 24

2.1 Procedures of determination the volume of Gas influx ............................................................... 25

2.2 The calculations of Kick Tolerance of the Thesis Well- Example 1 ........................................... 32

2.2.1 The calculations steps ........................................................................................................... 32

2.2.2 Calculation Assumption ....................................................................................................... 32

2.3 Kick Tolerance Formula used in calculations ............................................................................. 33

2.4 Thesis Well Data In a Table ........................................................................................................ 35

2.5 Kick tolerance in planning phase ................................................................................................ 36

V

2.6 Kick Tolerance Application Example ......................................................................................... 38

2.7 Choke and Kill lines Effect in the Thesis Well .......................................................................... 41

2.8 The calculations of Kick Tolerance of the Thesis Well- Example 2 ........................................... 43

2.9 Kick Identification Chart ............................................................................................................. 49

2.10 Kick Circulation with Driller’s or Wait and Weight method .................................................... 49

3. Conclusions ...................................................................................................................................... 51

References ............................................................................................................................................ 54

Literature ............................................................................................................................................. 54

VI

List of Figures

1.Figure 1. Exploration/Delineation Well Planning ................................................................................ 2

2.Figure 1.1 Fracturing gradient ([1] Rabia et al 1985, modified by Alan Y. Othman) ......................... 4

3.Figure 1.2. Definition and Mechanism of Stresses ............................................................................... 6

4.Figure 1.3. Definition and Mechanism of Horizontal and Vertical Stresses (Tan Nguyen et al 1987) 7

5.Figure 1.4 Geostatic pressure gradient, fracture pressure gradient, pore pressure gradient against the

depth ([1] Rabia et al 1985) ..................................................................................................................... 8

6.Figure 1.5 Reductionin the Formation Breakdown Gradient as the hole deviation increases. This

figure is based on a data from a North Sea well reduction in FBG FIG ([1] Rabia et al 1985) ............ 10

7.Figure 1.6 Casing Seat Selection ([1] Rabia et al 1985) ................................................................... 12

8.Figure 1.7 Construction of Overburden Gradient ............................................................................... 13

9.Figure 1.8 Casing Seat Selection- Well Construction ([1] Rabia et al 1985) ..................................... 14

10.Figure 1.9 Determination of casing show depth on the bases of maximum mud weight-Well

Engineering and Construction ([1] Rabia et al 1985) ............................................................................ 15

11.Figure 1.11 Kick tolerance when the well shut-in (the author'sown work) ...................................... 17

12.Figure 2.2 Plot influx volume vs. permeability (the author's own work) ......................................... 26

13.Figure 2.4. Formation height vs. Influx Volume (the author’s own work) ...................................... 28

14.Figure 2.6. Kicktolerance vs. Fracturing Pressure (Formation Pressure = Constant) ...................... 30

15.Figure 2.11 Planned casing shoe depths seat selection by depended on requested kick tolerance

volume ([4] ENI - E & P el al 2006) ..................................................................................................... 38

16.Figure 2.12 TW-1 Well Construction (the author's own work) - if the total depth and the Pore

gradient changed for hole size 81/2” and casing 95/8’’ ........................................................................ 39

17.Figure 2.14 Second section of thesis well construction of 9 5/8” Casing and 8 ½” hole size With

difference in TD, m and PG, Kg/l (the author's own work) .................................................................. 40

18.Figure 2.15 Kicktolerance Vs. Pore pressure gradient (the author's own work) .............................. 40

19.Figure 2.18 Thesis Well Example 2 – Construction (the author's own work) .................................. 44

20.Figure 2.19 (the author's own work) ................................................................................................ 46

21.Figure 2.21 (the author's own work) ................................................................................................ 48

22.Figure 2.22 Kick Identification Chart .............................................................................................. 49

23.Figure 2.23 Kick Circulationwith driller’s or wait and weight method ........................................... 50

1

Introduction

Kick Tolerance is an important factor in the industry, that allows drilling engineerstoestablish

several parameters in the development phase of a well, such as casing depths, open hole

lengths, etc. It can also be considered a valuable safety factor to prevent well control

problems.

Several different definitions and calculation approaches were found for this term, and when

you have something as dynamic and fast-paced as it is the oil & gas industry it is an important

issue, since this lack of standardization leads to confusion and miscommunication.importance

of kick tolerance in well operations has recently increased due to its implications in well

design, in drilling and well control. These implications are still more evident in wells

currently drilled by oil industry, for which more complex planning and execution are required

in comparsion with the past.

Now days, the oil & gas industry is faced with an increasingly difficult challenge, the

complexity of drilling operations is greater every day and this is an irreversible tendency. This

trend, associated with extreme pressure and temperature conditions, remote and harsh

operating environments, combined with associated risks due to small margins, high

investments and a very much-needed strong focus on safety, calls for more detailed well

planning.As defined by NORSOK D-010, Well Integrity is the:

Application of technical, operational and organizational solutions to reduce risk of

uncontrolled release of formation fluids throughout the life cycle of a well.

The ability to ensure well integrity requires a throughout understanding of the corresponding

well behaviour and how it is affected by the different operational regimes it is subjected to,

during all phases of a drilling operation. To achieve best possible well integrity, through

planning, good software tools are essential.

2

1Figure 1. Exploration/Delineation Well Planning

Figure1.shows a simplified model of the steps involved in the planning of a well, it start with

the knowledge of the different formation pressures and the original objectives of the drilling

campaign, all this informations then is taken into consideration as the design team moves

forward to advanced stages of the development.

Kick tolerance is a key element when establishing a well design. The number of sections will

rely on the engineered data from the set of regulations governing the safety (kick tolerance)

for each section.

It is the aim that the methods presented in this chapter can be used directly in well designs and

field operations with little modifications. Although, there is a great deal of maths required to

explain some of the ideas presented here, the chapter gives the minimum amount of

mathematical derivations to keep the book practical.

3

1 Theory of KICK Tolerance

This chapter is useful and important to focus on, while well design and construction and

calculating the kick tolerance.

1.1 Formation Integrity test

The term Formation Integrity is one of the most widely misused terms in the oil industry. It is

usually used to indicate a test to determine the fracture gradient. In reality, the term Formation

Integrity Test has a more encompassing meaning which includes:

Limit Test: A test carried out to a specified value, always below the fracture gradient of the

formation.

Leak off Test: A test carried out to the point where the formation leaks off.

Fracture Gradient Test: A test carried out to the leak off point and beyond until the formation

around the wellbore fails.

Another term widely used is the Shoe Bond Test which is carried out to test the strength of the

cement at the casing shoe. There is no theoretical basis to this test other than deciding on a

cement strength value and carrying a test to this value.

This Chapter will be mainly concerned with Fracture Gradient determination as the other tests

become merely derivatives if this test is carried out completely. For example, if a leak off

tests is carried out to full formation fracture then this test gives three values: leak off value,

formation breakdown strength and fracture gradient value, Figure 1.1 We will use the term

Formation Integrity Test (FIT) to describe the test irrespective of what value is eventually

determined

1.2 Formation Integrity Test:Purpose

The main reasons for performing a formation integrity test (FIT) are:

(a) To investigate the strength of the cement bond around the casing shoe and to ensure that

no communication is established with higher strata.

(b) To approximate fracture gradient and therefore establish the upper limit of primary well

control for the following open hole section.

(c) To investigate well bore capability to withstand pressure below the shoe in order to

validate or invalidate the well plan with respect to the following casing shoe setting depths.

(d) To collect regional information on the formation strength for optimisation of well design

for future wells (Fig1.1).

4

2Figure 1.1 Fracturing gradient ([1] Rabia et al 1985, modified by Alan Y. Othman)

1.3 Fracturre Gradient Determination

In oil well drilling, the fracture gradient may be defined as the minimum total in situ stress

divided by the depth.

The accurate prediction of fracture gradient is essential to optimising well design. At the well

planning stage, the fracture gradient can be estimated from the offset well data. If no offset

well data is available then fracture gradient can be predicted using any of several published

models. The most widely used predictive method is the Hubbert and Willismethod [2] as

outlined in “Predicting Fracture Gradient” As the well is drilled, Formation Integrity Tests

(FIT) are carried out to determine the approximate value of fracture gradient beneath the

casing shoe.

The FIT pressure is converted to an EMW which determines the upper limit of primary well

control for the next hole section. FIT limit tests are not designed to break the formation but

merely to reach the value of the least horizontal stress. The value of the least horizontal stress

is the Fracture Gradient at the point the test is carried out. FITs are typically carried out once

in each open hole section after drilling out the casing shoe.

The test should be repeated when weaker zones are drilled into as this lower fracture gradient

may have a vital impact on well design and primary well control. However, it is not always

possible, practical or desirable to repeatdrilled into as this lower fracture gradient may have a

5

vital impact on well design and primary well control. However, it is not always possible,

practical or desirable to repeat FITs at every formation change. Hence it is useful to be able to

predict the fracture gradient of new formations whilst drilling to assess impact on the well

plan and determine potential low fracture gradients which may require further FIT analysis.

1.4 Theory of wellbore breakage

The creation of a well in the ground will disturb the in-situ earth stresses and will actually

induce stresses around the wellbore. The induced stresses exist across a thin shell around the

wellbore and will increase the strength of the wellbore. This increased strength (or stress

raisers) due to drilling a hole in a medium is a well established idea in Mechanical.

Engineering and was borrowed by Drilling Engineers about fifty years ago. Essentially then if

one attempts to pressurise a wellbore and if a graph of pressure vs. volume pumped is

established then a linear trend will initially be seen, Figure1.1 If the test were to continue at

higher pressures, then theoretically the wellbore will fracture when the pressure reaches the

minimum horizontal stress. However, as the wellbore strength has been artificially increased

by the presence of the wellbore it will take pressure in excess of the minimum horizontal

strength to fracture the wellbore. The pressure required to rupture the walls of the wellbore is

called the Formation Breakdown Pressure. Once this pressure is exceeded and a fracture is

generated in the virgin rock, then the pressure required maintaining the fracture will be less

than Formation Breakdown Pressure.

On the graph (Figure 1.1), this is seen as a drop in pressure. The constant pressure required to

propagate a fracture is called the Fracture Propagation. When planning exploration or wildcat

wells, where there is little or no reliable offset well data, the fracture gradient can be

estimated using various predictive techniques. In addition, when drilling a well, fracture

gradient should be calculated for each new lithology drilled. It is usually assumed that the

fracture gradient at the casing shoe is the lowest within the open hole section.

The assumption that fracture gradient is lowest at the previous casing shoe is not necessarily

true. As previously discussed, fracture gradients vary with the in-situ stresses (overburden,

pore pressure etc.), superimposed tectonic stresses and formation type. Hence the lowest

fracture gradient in an open hole section is not always found at the previous casing shoe. a

repeat FIT test. The kick tolerance and MAASP are always based on direct measurement of

fracture gradient. This can have severe implications for the well control practice and casing

6

setting depths. Fracture gradient estimates made whilst drilling are normally the responsibility

of the mud logging contractor. The estimates made should be used to establish a predicted

leak-off pressure prior to conducting an FIT. When the predicted fracture gradient is

dangerously close to the maximum anticipated mud weight, consideration should be given to

performing a repeat FIT test. The kick tolerance and MAASP are always are always irect

measurement of fbased on dracture gradient.

1.4.1 Hubbert and Willis Method

The Hubbert and Willis method [2] is based on the premise that fracturing occurs when the

applied fluid pressure exceeds the sum of the minimum effective stress and formationpressur.

The fracture plane is assumed to be always perpendicular to the minimum principa stress

Figure1.2.

The definition and mechanism of fracture formation pressure are:

Fracture pressure is the pressure in the wellbore at which a formation will crackThe stress

within a rock can be resolved into three principal stresses. A formation will fracture when the

pressure in the borehole exceeds the least of the stresses within the rock structure. Normally,

these fractures will propagate in a direction perpendicular to the least principal stress.

3Figure 1.2. Definition and Mechanism of Stresses

(reference: New MexicoTech by Tan Nguyen et al 1984)

7

At sufficient depths (usually below 1000 m or 3000 ft) the minimum principal stress is

horizontal; therefore, the fracture faces will be vertical. For shallow formations, where the

minimum principal stress is vertical, horizontal (pancake) fractures will be created Figure1.3.

4Figure 1.3. Definition and Mechanismof Horizontal and Vertical Stresses(Tan Nguyen

et al 1987)

And according to the relation ship between the well depth and the pressure through the Well

section the Fracture Pressure Gradient will be the line in the middle between the Pore Pressure

Gradient (Normal).PGr = 0.465 psi/ft

Geostatic Pressure (Overburden Pressure) Which the Fracture Pressure Gradient increase with

increasing the depth.TheFigure1.4 shown the physical relation ship.

8

5Figure 1.4 Geostatic pressure gradient,fracture pressure gradient, pore pressure

gradient against the depth ([1] Rabia et al 1985)

According to the Hubbert and Willis method [2], the total injection (or fracturing) pressure

required to keep open and extend a fracture is given by equation :

FG = (1.1)

Where is the effective minimum principal stress (= minimum principal stress minus pore

In terms of overburden gradient, Poisson’ ratio () and formation pressure, the above equation

becomes:

FG =(v/1-× f)/D + Pf/D (1.2)

Example Fracture Gradient Calculation

Calculate from bulk density logs? And Estimate the formation fracture gradient at (6200 ft)?

If the formation pressure at (6200 ft) is (2500 psi) and overburden stress is (1 psi/ft) .

Solution : FG = (/1-) (

FG = (0.4/1-0.4) (6200 – 2500) +2500 FG = 4967 psi

FG = 4967 psi / 6200 ft FG = 0.8011 psi/ft

1.5 Formation Breakdown Gradient :

Knowledge of the formation breakdown gradient (FBG) is of paramount importance during

kick situations when the casing shut-in pressure, CSIP, is being monitored, so that the sum of

the hydrostatic pressure of fluids in the annulus and CSIP is always kept below the FBG at the

9

casing shoe. It may be argued that, for added safety, control should be based on the fracture

propagation pressure (= ) rather than the FBG. However, in deviated wells and in areas

where is considerably different from 2, the calculated FBG can be lower than 3.

FBG = 3 – + T – Pf(1.3)

T : Rock tensile strength

Equation (1.3) is only valid when no fluid invades or penetrates the formation. In porous and

permeable rocks the drilling mud normally penetrates the formation, thereby changing the

magnitude of the stress concentrations around the borehole. The effect of fluid penetration is

to create a force radically outward which reduces the stress concentration at the walls of the

hole, thereby making it easier to fracture the wellbore. Haimson and Fairhurst10 modified

Equation (1.3) to take into account the effects of fluid penetration, to obtain Formation

Breakdown Gradient:

FBG = (3 – + T)/(2 – α(1 -2/1- )) – Pf ( 1.4)

Where α = 1- (Cr/Cb), Cr =the rock matrix compressibility

Cb = the rock matrix compressibility, and 0.5 ≤ α ≤ 1 when 0 ≤ ≤ 0.5 and finally.

0 ≤ α(1 -2/1- ) ≤ 1

Haimson and Fairhurst10 refer to the formation breakdown pressure as fracture initiation

pressure. Hence, when α [1- 2 / 1-] = 1, Equation (1.4) reduces to Equation (1.3) for the

case of no fluif penetration.

= Vertical Stress

= two horizontal stress

Ʈ = Shear stress

1.6 Effects of hole deviation on Formation Breakdown Gradient

All the previous equations were derived for the case of vertical holes in which the vertical

principal stress had no influence on the magnitude of fracture pressure. However, as the hole

starts deviating from vertical, the overburden stress starts contributing to the fracture pressure,

thereby reducing the magnitude of the formation breakdown pressure:

10

FBP = 3 (3 – cos 2α ) – 1 sin

2α + T – P ( 1.5)

6Figure 1.5 Reduction in the Formation Breakdown Gradient as the hole deviation

increases. This figure is based on a data from a North Sea well reduction in FBG FIG

([1] Rabia et al 1985)

1.7 Casing Seat Selection

Accurate knowledge of pore pressure and fracture gradient plays a major role in the selection

of proper casing seats which would allow the drilling of the next hole without fracturing. Pore

pressure, mud weight and fracture gradient are used collectively to select proper casing seats.

The following example illustrates a method for the selection of casing seats.

Example (2) Casing Seat selection: Determine the fracture gradient at the various depths using

Equation (1.2). Assume = 0.4. Using the data in table 1 and 2:

(1) (2)

Depth below sea level (ft) Pore pressure (psi)

2000 1250

4000 2380

7200 4060

7500 4500

8000 5950

8500 6790

9000 7750

9500 10100

0. 1Table 1

Solution:The following steps may be used to complete colomns 3-6 of Table2

(1) The required hydrostatic pressure of mud is taken as equal to pore pressure + 200 psi,

where 200 psi is the magnitude of overbalance. Any reasonable value of overbalance may be

used.

(2) Calculate the pore pressure and mud pressure gradients by simply dividing pore pressure

and mud pressure by depth to obtain gradient in psi/ft.

11

(3) Calculate the fracture gradient by use of Equation (1.2):

1 2 3 4 5 6

Depth

below sea

level (ft)

Pore

pressure

(psi)

Mud

Pressure =

Pore

Pressure +

200 (psi)

Pore

pressure

gradient

(psi/ft)

Mud

pressure

gradient

(psi/ft)

Fracture

Gradient

(psi/ft)

2000 1250 1450 0.625 0.725

4000 2380 2580 0.595 0.712

7200 4060 4260 0.563 0.591

7500 4500 4700 0.600 0.626

8000 5950 6150 0.743 0.768

8500 6790 6990 0.798 0.822

9000 7750 7950 0.861 0.833

9500 10100 10300 0.960 0.980

1. TableTable 2

FG =(v/1-)× - f)/D + Pf/D

By use of = 0.4, this equation becomes:

FG = 2/3[ - Pf / D] + Pf/D

Where is the pore pressure gradient? Taking [ psi/ft, and using Table (2) the

FractureGradient at 4000 ft is calculated as follows:

FG = 2/3 (1 – 0.595) + 0.595 = 0.865 psi/ft.

The same equation can be used to calculate FG at other depths shown in the same table.

1.8 Casing Sea Selection Steps

1. On the same graph paper, plot the pore pressure gradient, the mud pressure gradient and the

fracture gradient against depth as shown in Figure1.6.

2. Starting at hole TD (11 000 ft), draw a vertical line through the mud gradient until it

intersects the fracture gradient line. In our example the mud gradient at TD is 0.94 psi/ft and a

vertical line through it (line 1 in Figure 1.6 intersects the fracture gradient line at 10 500 ft

(point A in Figure1.6. Above 10 500 ft, the mud weight is required. Hence, between 10 500 ft

and 11 000 ft the open hole should be cased with either a production liner or a production

casing.

3. Above 10500 ft the hole must be drilled with a mud weight less than 0.94 psi/ft. The new

mud gradient is obtained by drawing a horizontal line from point A to the mud gradient line.

Point B in gives the new mud gradient as 0.88 psi/ft Move vertically from point B until t

Figure1.6 he fracture gradient line is intersected at 8850 ft at point C. Point C establishes the

12

maximum depth that can be drilled before changing to the new mud gradient of 0.88 psi/ft.

Hence, between points B and C a protective liner should be used. Alternatively, an

intermediate casing can be set at point B.

4. from point C move horizontally to the mud gradient line to point D, where the mud gradient

is 0.68 psi/ft. A vertical line from point D shows that a hole can be drilled with a mud gradient

of 0.68 psi/ft to surface without fracturing the formation.Suggested casing types at the various

setting depths are given in Figure 1.6.

.

7Figure 1.6 Casing Seat Selection ([1] Rabia et al 1985)

1.9 Overburden pressure

The total weight is:

formation solids (rock matrix)

and formation fluids in the pore space

Defined as the pressure exerted by the total weight of overlying the formations above

the point of interest.

Overburden Pressure: Figure1.7

Pov = 0.0981 x ρb x TVD

Pov = overburden pressure, bar (psi)

ρb = formation bulk density, kg/l (ppg)

13

TVD = true vertical depth, m (ft)

Pov = 0.052 x ρb x TVD

8Figure 1.7 Construction of Overburden Gradient

Pressure concept([3] Imre Federer et al 2012)

1.10 Casing Seat Selection based on methodology for design setting depth of

surface and intermidate casing stringin a gas well:

The pressure at the casing seat must be able to withstand is the greater of:

The hydrostatic pressure of the mud used to drill the next section.

The maximum pressure exerted at the casing seat when circulating out gas influx from

TD of the next hole section.

The selection of casing setting depths is one of the most critical in the well design process.

And the geological background:

Drilling data from offset wells

Key factors:Information is sourced from:

Seismic

Pore pressure determination

Fracture gradient determination

14

9Figure 1.8 Casing Seat Selection- Well Construction ([1] Rabia et al 1985)

For exploration wells, it is preferable to use offset well data to select casing seats for the well

under consideration. If this data is not available, then the casing seat depth may be determined

using the following methods:

(a) The FBP or fracture gradient data together with pore pressure and mud weight should be

plotted against depth as shown in Figure1.8the shallowest casing setting depth is point X. The

FBP or fracture gradient data together with pore pressure and kick circulation pressure should

be plotted against depth as shown in Figure1.8. The shallowest casing setting depth shallowest

casing setting depth is Y point

In fig (1.9): Shown the determination of casing shoe depth on the bases of maximum

mud weight.

15

10Figure 1.9 Determination of casing show depth on the bases of maximum mud weight-

Well Engineering and Construction([1] Rabia et al 1985)

1.11 Kick Tolerance

For practical purposes, kick tolerance may be defined as the maximum kick size which can be

tolerated without fracturing the previous casing shoe. Kick tolerance may also be defined in

the terms of the maximum allowable pore pressure at next TD or maximum allowable mud

weight which can be tolerated without fracturing the previous casing shoe.Table (3) gives

typical kick tolerance values for exploration wells. Kick tolerance therefore depends on the

maximum kick size, maximum formation pressureat next TD and the maximum mud weight

which can be tolerated without fracturing the weakest point in the open hole, usually the

previous casing shoe. Other minor factors which affect kick tolerance include density of the

invading fluid and the circulating temperatures.

HOLE SIZE, inches KICK VOLUME , bbl

23’’ 250

171/2’’ 100-50

121/4’’ 50-100

81/2’’ 25-50

Table3 Typical Values Of Kick Tolerances From various Operators

16

1.11.1 KickTolerancewhenthe top of thekickatthecasingshoe

Figure 1.10. Kick tolerance when the top of the gas at the casing shoe

(the author'sownwork)

The theory which is involved in kick tolerance calculation.The first step to take is to

determine what the maximum height of the influx can be when it reaches the shoe

Fig1.10.The symbols in the picture represent:

D shoe = Depth shoe

TD = Total Depth

ρm = Mud density

ρi , kick zone = Influx density at the kick zone.

H shoe = Height of influx

At the shoe , the maximum pressure allowed is :

P shoe max = D shoe × LOT – P safety (1.8)

To reach this maximum pressure , the following equilibrium must apply :

P shoe max = Pf – ρm × (TD – D shoe – H shoe) –ρi, kick zone, shoe × H shoe

17

This means that the height of the kick at the shoe can be determined as :

H shoe = [P shoe max – Pf + ρm× (TD – D shoe)]/ ρm – ρi, kick zone, shoe

This height represents a certain volume :

V shoe = H shoe × A ann, shoe

With:

Ann, shoe = Surface area at the shoe

The influx volume at the shoe originates from an influx volume at the kick zone which

correspondes to :

V kick zone = V shoe × [ P shoe max / Pf ]

This is the first kick tolerance value. This is the influx volume at the kick zone which

will cause the pressure at the shoe to reach the maximum allowable value when the

kick reaches the shoe.

Kick tolerance when thewell is shut-in

However, we also consider the possibility that the pressure at the shoe can reach the

maximum allowable value when the kick enters the wellbore Figure1.11. This volume, the

second kick tolerance value, could well be smaller than the first kick tolerance value, because

of smaller annular capacity. But it could also be higher because of a bigger indication of the

kick zone. Therefore we have to calculate this second kick tolerance value as well.

11Figure 1.11 Kick tolerance when the well shut-in(the author's ownwork)

18

TD = Kick zone depth

D shoe = Shoe Depth

H kickzone = Height of influx at the kick zone

ρm = Mud density

ρi kick zone = Density of influx at the kick zone , half the way of the height of the influx.

The same equations as for the kick tolerance calculation apply for this equation, so to reach

the maximum allowble pressure the following equlibruim must apply:

Pshoeamx = Pf – ρm× (TD – Dshoe –H kick zone) – (ρi, kick zone × H kick zone)

This means that the height of the influx at the kickzone can be defined as the:

H kick zone = P kick zone – Pf + ρm(TD – D shoe) / (ρm–ρi, kick zone)

Again this height represents a particular volume:

V kick zone, 2 = H kick zone × A ann, kick zone

With

Anann, kick zone = Surface at the kick zone.

The final kick tolerance is defined by which of either of the two kick tolerances is the smallest

If V kick zone, 1> = V kick zone, 2 then V kick zone, 2 = Final Kick Tolerance

Else V kick zone, 1 = Final Kick Tolerance

1.12Gas Influx: ideal gas law or standing – Katz Z factor

In the base case we olready so the basic equations to calculate the kick tolerance for a gas

kick. As a gas is compressible the volumes are pressure dependend and thus the density .The

kick tolerance calculator has two gas types’ options:

1. The ideal gas option which uses the ideal gas low to calculate the gas density

2. The methane gas option which uses the stnding Katz Z factor to calculate the density of

methane gas for the input parameter.

1.12.1Gas influx idal gas law

The ideal gas low is stated as follows

PV n RT

And thus defines the gas density as

ρ = ( n/V) = ( P/ RT)

Although the ideal gas low has a tempreture term in it, the tempreture term has been left out

of the ideal gas method this means that the followigsasumption is made:

T shoe = T kick zone

19

With

Ρi, shoe = ρi, kick zone × [(Pshoemax / Pf) × (T kick zone / T shoe)]

Then, ρi, shoe = ρi, kick zone × (Pshoemax / Pf)

In a normal situation the tempreture at the show will be the lore than the kick zone, so the

consiqunse this assumption will have , is the density of the gas at the show will be calculated

lighter than is actually is . So this assumption only makes the kick tolerance calculation more

conservative. This method used in the base cased the rest of calculations for the ideal gas

method is based on the same theory and equations mentioned in the base case.

1.12.2 Gas influx the standing Ktz Z factor

In the methanne gas method the gas densities are calculated by means of the standing Katz

equations of state this equation of state is based on the ideal gas law , but is has and extra gas

compressibility term . The z factor added to it. Inisially the equation of state is defined as

PV = n ZRT

standing and Katz came up with a chart to be able to determine the z factor for

differntparmeters, Hall and Yarborough, oil and gas, developed a method to calculate this

factor by means of a Newton – Raphson technique .in this section we will not go in to the

finar details of thi method but simpy present the global equations in reference to the relevent

articles .the calculations based on the following equations:

Z = P / ρ RT y = b ρ / 4

Z = (1+y+y2+y3) / (1-y)3 – [14.76t – 9.76t2 + 4.58t3] ×y + [90.7t – 24.2t2 +42.4t3] ×

y(1.18+2.82t)

b Pc / RTc = 0.245 exp [ - 1.2 (1 – t)2 ]

When these equations are substutide in one another following functions F arises :

F = - 0.06125 Pr t exp [-1.2(1- t)2 ] + [y+y2+y3+y4/(1- y3)] – (14.76t -9.76t2+ 4.58t3) y2 +

(90.7t – 242.2t2 + 42.4t3) y(2.18+2.82t)

With

t = T / T c = Reduce Tempreture

Tc = Critical Tempreture

And

Pr = P / Pc = Reduce pressur

20

This equation is none –linear and can be solved with earlier mentioned Newton

Raphsonmethos be approximating F for a first order Tillor, s serious a bout a small initiall

value F(0)

ForY (0)

0 = F Approx = F(0)

+ ( dF(0)

/ dy) × (y – y (0)

)

This equation can be solved for a new value of Y which can be used to re-evaluate F and

itterateduntillF (0) is less than some small number and thier by giving a solution for Y and

thus Z factor and the gas dnsity. Returning to our base case the calculated gas densities are

used to determine kick tolerance values 1, 2 instead of using the formation pressure and the

mximum shoe pressure the volume at the shoe is convrted to bottom to obtain kick tolerance

volume 1 in the followingequation:

V kick zone = V shoe × (ρi, shoe / ρi, kick zone)

1.12.3 Calculation through the profile

2.TableTable4. (the author'sown work)

Theory of kick tolerance reference

Remember the well profile input we will use the sample above, to explain the theory behind

the calculations, the minimum capture method. To be able to calculate the TRUE vertical

depth Table 4 .for station to we need the input and calculating values for station 1.

d 2 = acos [cos ( In2– In1) – sin (In2) sin(In1) ×{1- cos (Az2 –Az1) }]

Then we calculate r

r2 = dl2 tan (dl2 / 2)

If the dogleg is zero then r is set as 1 next the tvd for station 2 is calculated

TVD2 = TVD1 + [MD2 – MD1 / 2 {cos (In2) + cos (In1)} × r2]

1.12.4 True vertical depth for the shoe and the kick zone

Determining the true vertical depth for the shoe and the kick zone follows the same

procedures lets say that the measure depth for the shoe is between the station 1 and 2 .to

determine the TVD we have to interpulate between the sttion 1 and 2 find the measure depth

MD and inclination as azimuth for this point so we can calculate a TVD.

MD Incl. Azim. DL DLS TVD

1 5000 40.000 0.000 40.0 2.0 4841.45

2 7000 40.000 0.000 0.0 0.0 6373.54

21

The meassure depth we are seaking the TVD for, we call the interpulation point IP

MD = MD2 – MD1 dMD = IP – MD1

Then, dl = dl2 × (dMD / MD)

Next we convert the inclination and assimuth input from carthesiancoardinates to

pollarcoardinates in a carthesian system

1 = sin In2 cos Az2

2 = sin In2 sin Az2

3 = cos In2

u 1 = sin In1 cos Az1

u 2 = sin In1 sin Az1

u 3 = cos In1

x1 = u2 3 – u3 2

x2 = u3 1 – u1 3

x3 = u1 2 – u2 1

k = ( x12 + x22 + x32)½

x 1 = x1 / k x2 = x2 / k x3 = x3 / k

y1 = u2 x3 – u3 x2

y2 = u3 x1 – u1 x3

y3 = u1 x2 – u2 x1

y1 = y1 / k y2 = y2 / k y3 = y3 / k

k = (y12 + y22 + y32 )½

z1 = u1 z2 = u2 z3 = u3

Now we convert back from polar tpcarthesiancoardinate

H2 = - sin(d)

H3 = cos(d)

w 1 = H2 y1 + H3 z1

w 2 = H2 y2 + H3 z2

w 3 = H2 y3 + H3 z 3

Now we determine the inclination and azimuth for interpolation points :

In = arctan [(w12

– w22) / w3]

½

Az = arctan [|w2 / w1|]

If w1< 0 and w2< 0 , then Az = 180 + Az

22

If w1< 0 and w2> = 0 , then Az = 180 – Az

If w1> = 0 and w2< 0 , then Az = 360 – Az

If w1> = 0 and w2> = ,then Az = Az

Further more we determine the dogleg severity DIS

Dls = dl / (MD2 – MD1)

And at last we calculate the TVD for interpolation points:

r = tan (dl) / dl

dTVD = dMD / 2 ( cos In 1 + cos In ) r

TVD = TVD1 + dTVD

However if the inclination and assimuth for station 1 and 2 are the same true vertical depth

can simply be determined by:

TVD = TVD1 – (dMD / MD) [TVD2 – TVD1]

1.12.5 Calculation the meassure length for the influx heights at the shoe and the kick

zone

To determine the measure length for the influx height , we have to determine the measured

depth of either the bottom and the top influx .(depending if your looking at the shoe or the

kick zone 0. only at the step value is taken for the meassure depth for each step the TVD is

calculated and compared to what it should be and thus suing the calculation method as the

program keeps on calculating the TVD untill the TVD which we are aiming for is reached

(between certain limits )now that we have optaint the measure length of the influx heights we

can finially calculate influx volumes with :

V shoe = M shoe × Aann, shoe

V kick zone, 1 = V shoe × ( ρi, shoe / ρi, kick zone )

V kick zone, 2 = M kick zone × A ann, kick zone

M kick zone = measured length of influx at the kick zone.

If V kick zone, 1 greater than V kick zone, 2 then V kick zone, 2 = final kick tolerance

Else V kick zone, 1 = final kick tolerance.

1.13 Kick tolerance elements

Limited Kick Method: Main problem is knowing which realistic value for kick size to use for

each hole size.

The following elements determined the magnitude of :

Pore pressure from next TD

23

Mud weight to be used

Fracture Gradient at current casing shoe

Volume of Influx volume that can be safely circulated out

Type of well: exploration or development

When to calculate Kick Tolerance :

After a Leak-off test ( LOT)

ApriortAo drilling ahead

If the mud weight is changed

When drilling into areas of over pressure :

Rapid pore pressure increase , Increasing mud weight to compensate,

Kick tolerance is limited by formation strength at the previous casing shoe.

To calculate the Kick Tolerance :

For the purpose of well design and monitoring of wells with potential kick capability.

Kick tolerance should be calculated in terms of kick volume which can be circulated

out without fracturing the previous casing shoe.

The end of the chapter one of my THESIS will be the way which leads me to calculate

the KICK TOLERANCE of vertical GAS well at the CASING SHOE and the

BOTTOM HOLE by depending on the last (13) main points. By using well data and

going a head with the procedures of calculations, focus on the best conclusion which it

recovered from the calculations it called a planning of WELL DESIGN,

CONSTRUCTION and calculating the KICK TOLERANCE.

24

2. Calculation of casing shoe depth determination taking into consideration

The Kick Tolerance and Well Integrity

Calculation will be introduce with the TW-1 (Thesis Well-1)data that are given in the Figure

2.1

Figure2.1TW-1 Well Construction (the author's own work)

25

2.1Procedures of determination the volume of Gas influx

Influx into thewellbore

Q (bbl/min) = [ 0.007× K × P × L] / [µ × In(Re / Rw) × 1440 ] (2.1)

Q: Flow rate, bbl/min

md: permeability , millidarcy

∆P: differential pressure, psi

L: length of section opens to the wellbore, ft

µ: gas viscosity. Cp (centipoise)

Re: radius of drainage, ft

Rw: radius of the well bore, ft

The Formation Data from the equation 2.1

K, mD: 550 mD

∆P, bar: 21 bar

L, m: 10

Re, m: 10

Rw, m: 0.10788

Ln (Re/Rw): 4.3998

By depending on the formation data, well drilling data , and the volume of influx data in

Table1.3 Typical values of kick tolerance from various operators, of 81/2” hole size the kick

tolerance will be from (25-50) bbls. Now the result will be the plot of:

Influxvolume vs. Permeability

3. TableTable5. Calculations procedures influx data of well of variable the permeability

(K),mD. (the author's own work)

26

12Figure2.2 Plot influx volume vs. permeability (the author's own work)

In Figure2.2 the permeabilities are consider variables, and the volume of influx changed with

the time changing. At the 20 minutes we got high volume of influx 183.69 m3 which was not

required for 81/2 ’’ hole size,therfore, if we check the influx volume at 10.15 minutes we see

the plot give us the required volume of influx which is 25 m3 with permeability 900

mD,therfore we conclude that the increasing of time will increase the volume of influx, so

drilling in deep increase the volume infux by depending on drilling time.

27

Influx volume vs. Penetration into formation

4. TableTable6.Calculations procedures influx data of well of variable length of section

into the wellbore (the author’s own work)

Figure2.3 Plot Influx volume vs. Penetration intoformation (the author’s own work)

In Figure2.3 The plotting of volume influx against the hole depth in 81/2” hole size we see

that the number of feet of hole drilled are variables, so with increasing the depths we will get

high volume of influx with time is go on if we see the yellow curve in the plotting we see

after 20 minutes of drilling the volume of influx is 27.39 m3 , through the interpolation of

time between 19 and 20 minutes exactly at 19.50 mintues we see the required volume ofinlux

25 m3 at the depth 24.50 ft.

28

Formation height vs. Influx volume

5.Table7. Calculations procedure sinflux data of well through tripping

13Figure2.4. Formation height vs. Influx Volume(the author’s own work)

In Figure2.4 we see the effect of the vertical thickness of formation on the volume of influx

throgh the tripping Pulled Out Of Hole POOH and Run In HoleRIH, then in like of this type

of situations the mud density has important role, so through POOH the level of muddecrases

and lead to decrease the hydrostatic pressure of mud,therfore, the probability of influx will be

expect especially if we have long formation thickness. However the height of formation is

more the volume of influx will be more too. If we see the yellow curve 50 ft height of

29

formation,the volume of influx is 22.71 m3 and decrase comparing with the last two plots of

Figures 2.3 and 2.4 the analysis is through tripping of POOH we have to fill-ups the well with

mud after the numbers of stands pull according to the project number of stands pulling,thus

the probability of formation influx will decrease because we control the well by the mud and

protect Bottom Hole pressure BHP which will consider the priamary well control throgh

tripping.

Kick Tolerance vs. Formation Pressure

Figure2.5 Kick Tolerance vs. Fromation Pressure

(LOT= Constant)(the author's own work)

In the Figure2.5 Show the kick tolerance at the casing shoe because we have the different

variables of Leak-Off Test ( LOT) on the right side of the figure,so we see how the volume of

influx will change with the increasing or decreasing of formation pressure Pf if the LOT is

constant. If we look at the bold black line in the center of figure, by depending on the values

of kick tolerance above and under the line we can used abest casing seat selection, so above

the line there are a big values of kick tolerance with increasing the formation pressure values

inversly situation under the line

Kick Tolerance vs. Fracturing Pressure (LOT)

30

14Figure2.6. Kick tolerance vs. Fracturing Pressure (FormationPressure = Constant)

(the author's own work)

In the Figure2.6we can say it is considering the inversly situation with Figure 2.5, so the LOT

have variables changing with fracturing pressure, then if we have a fracturing pressure the

LOT will change because the Pf is constant,therfore, with increasing the fracturing pressure

the value of LOT will increase also.The curves of Pf has aconstant values,if there intercept

with blod black line which refers to 30bbls that time we can get an exact value of LOT or

fracturing pressure which is best idea to choose the best casing seat selection.

31

Shoe Depth Vs. Kick Tolerance

Figure2.7. Shoe depth vs. Kick Tolerance (the author's own work)

In the Figure2.7gives the informations to choose the casing shoe depth by depending on the

values of volume of influx. The yellow curve gives influx volume changing thrugh drilling

according to the casing shoe depth,so if we make interception of the required kick tolerance

value for example 2.50 m3 with the influx changing values in the yellow curve we will see

they meet at the point of 1.89 m3 the variable kick tolerance, then we will get 880 m shoe

depth which is the best shoe depth for casing seat shoe.

32

2.2 The calculations of Kick Tolerance of the Thesis Well- Example 1

To calculate the Kick Tolerance and investigation of casing shoe depth of the well,inmy thesis

I depended on two type calculators:

Good Kick Tolerance Calculator which I used it in 2.2 Procedures of determination the

gas volume influx.

Kick Tolerance Calculator- ENI Exploration and Production (E & P) [4] which I will

use it int he other’s step of Thesis Well Calculation.

2.2.1 The calculations steps

The amount of influx volume that entering in well depends on:

Underbalance between mud weights and pore pressure.

Reservoir porosity and permeability.

Influx type.

Sensibility and reliability of detection equipment.

Reaction time of well control crew.

Type well shut in procedure.

Time of BOP closure.

The same kick tolerance between two wells may not mean that they share the same level of

risk because it is important to consider how quickly an influx will grow!

2.2.2 Calculation Assumption

It has been assumed:

Vertical well.

Single monophase gas bubble.

Two drill string diameters (drill collar and drill pipe).

One open hole size.

Constant ECD profile.

It has been neglected:

Gas velocity and its real distribution inthe annulus.

Pressure and Tempreture influence on mud weight and influx gradient.

Gas composition, dispersion and solubility.

Driller’s method has been used for thecalculation.

These assumptions assures a conservative (safer) kick tolerance.

33

2.3Kick Tolerance Formula used in calculations

Two mirror approaches have been performed in order to obtain a correlation linking kick

tolerance volume to the corresponding pore gradient or kick intensity.

KI =( PG - MW) (2.2)

The correlation is biunique:

By fixing BHP (Bottom Hole Volume) it is possible to obtain the corresponding

increase of Pore Gradient.

By fixing PG (Pore gradient) it is possible to calculate the Bottom Hole Kick

Tolerance Volume.

Figure 2.8 Fixing Bottom hole Volume and Pore Gradient

(the author's own work)

34

1st Approach

By fixing BHP (Bottom Hole Volume) it is possible to obtain the corresponding

increase of Pore Gradient

Equation(2.3)

2nd Approach

By fixing PG (Pore gradient) it is possible to calculate the Bottom Hole Kick

Tolerance Volume.

Equation(2.4)

35

2.4Thesis Well Data In a Table

Well Data Value

Total depth TD,m 5000

True vertical depth TVD,m 4000

Casing shoe measured depth MD,m 3200

Casing shoe TVD,m 3000

Drill collar Length Dc L,m 190

Drill Pipe Length DpL,m 810

Drill Collar outside DiameterOD,inches 8 OD 2.813” ID

Drill Pipe outside DiameterOD,inches 5”

Mud Weight 1.6

Influx Gradient IG,Kg/l 0.3

Fracture Gradient FG,Kg/l 1.75

Hole size 121/4”

(the author's own work)

Table8. Thesis well data while the Hole size121/4” and Casing size 13 3/8”

These data are used to plot Kick Tolerance inthehole size 121/4” while casing is 133/8”. This

correlation is very incisive, especially in its graphical form.In this Figure2.9 the plotting Kick

tolerance against the Kick Intensity which is defined as the difference between the formation

pressure and current mud weight used in the wellbore. When you see the kick tolerance noted

in the drilling programs from town, drilling engineers normally calculate kick intensity at TD.

I want to explain two important situations in the Figure2.9:

If we have zero influx volume as show in the figure kick intensity 0.07 kg /l, that

time we have to depend on the value of MAASP maximum allowable annular

pressure shut-in the well and calculated the kick intensity from TD which called

Zero Kick Tolerance Volume.

If we have maximum kick tolerance volume 65 bbl in the figure, then the pressure

gradient PG and the mud weight MW are equalist, then we have Zero

underbalance (Swab Case), therefore the value of kick intensity is zero.

36

Figure2.9 Kick Tolerance plot of hole size 121/4”

2.5 Kick tolerance in planning phase

During the casing seat design, Maximum Allowable Annular Shut-in pressure (MAASP) and

Differential Pressure ∆P criteria are used to select casing seating points.

MAASP = [(FG – MW) × H shoe] / 10 (2.5)

∆P = [(MW–PG) × H Shoe] / 10 (2.6)

In Figure2.10 show the relation ship between the differential gradient pressure and the depth

by depending on the changing values of pore gradient pressure and fracturing pressure, as we

know that the pressure gradient has not relationship with the depth, therefore, the mud weight

has the big effect on the pressure gradient, so we see during the depth increasing the mud

weight increase also, then lead to increasing the pressure gradient of mud so the fracturing

pressure also increase with the pore gradient pressure according to the equation (P= FG-PG).

37

Figure 2.10 Relationship between Differential gradient pressure and the depth through

casing seat design ([4] ENI- E & P el al 2006)

Kick tolerance limits are fixed basing on diameter of the drilled open hole.

6. TableTable9.Kick tolerance volume according to the hole size([4] ENI- E & P el al

2006)

Int he Table 9 the values help the drilling engineer to verify the casing shoe depth. The

maximum pit gain used int he calculation is critical and must be selected as appropriate given

existing field operating practice, rig equipment, and the skills of the rig personnel. The

requested kick tolerance volume limits have to satisfy the planned casing shoe depths.In the

Figure 2.11 show how can we depended on the value of requested kick tolerance to plan for

casing seat selection depending on pore gradient pressure and the fracturing pressure.

38

15Figure2.11 Planned casing shoe depths seat selection by depended on requested kick

tolerance volume([4] ENI- E & P el al 2006)

2.6Kick Tolerance Application Example

In this case we are going to apply the example of kick tolerance of the thesis well by

depending ont he Table10 and casing 9 5/8” and hole size 8 ½” with changing some of

another data int he table like mud weight, fracture gradient and the length of drill collar.

7. TableTable10. Thesis well data while the Hole size 8 ½” and Casing size 9 5/8”

(the author's own work)

39

16Figure 2.12TW-1 Well Construction (the author's own work)-if the total depth and

the Pore gradient changed for hole size 81/2” and casing 95/8’’

(the author's own work)

The new result of kick tolerance application examplefor a new hole section with changing

some of the well data is:

Figure 2.13 Plot of Kick Tolerance (bbl) and Kick Intensity (Kg/l)

For the same Well Data while the pore pressure gradient change to 1.58 Kg/l wilth the

decreasing of the depth to 4000 m, showing in the Figur2.14.

40

17Figure 2.14 Second section of thesis well construction of 9 5/8” Casing and8 ½” hole

size with difference in TD,m and PG,Kg/l(the author's own work)

Result of plotting Kick Tolerance Vs. Pore Gradient

18Figure2.15 Kick tolerance Vs. Pore pressure gradient(the author's own work)

In the Figure2.15the required kick tolerance 25 bbl

Result of plotting 25 bbl the volume of kick tolerance vs. kick intensity

At pore gradient 2.05 kg/l as in the table 2.6 through interception with green curve

Of mud weight 2.10 kg/l we get the true value of kick tolerance volume which was

required for the example 1.

41

The conclusion from the Figure2.15 is introducing to the value of kick tolerance

volume by depending on the mud weight and pore pressure gradient.

Figure2.16 Kick tolerance Vs. Kick intensity(the author's own work)

In the Figure2.16 when we calculate the kick tolerance volume in the Figure2.15 during the

plot of pore gradient against the mud weight was 25 bbl,we see the changing in the kick

intensity in three times with changing in the mud weight in the Figure 2.16 if we plot kick

tolerance volume versus kick intensity, with three values of mud weight(1.90 , 1.95 , 2.00)

kg/l interception with 25 bbl kick tolerance volume, then the kick density at the influx time

willbe (0.02 , 0.06 , 0.10) kg /l.

The mud weight calculations in last plotting will be like showenin the table11.

8. TableTable11. Other parameters calculations in the thesis Well(the author's own

work)

2.7Choke and Kill lines Effect in the Thesis Well

The description of choke and kill lines consider the important factor in the offshore drilling

although in my thesis. I did not refer to the Offshore drilling because I choose my well thesis

at the Onshore drilling operations,but for showing the informations about the effect of choke

and kill lines in the investigation of casing shoe depth and the calculations of kick tolerance. I

decide to write something about the last main subject in 2.7.

42

Using the Table2.6 data we are going to plot Slow Circulation Rate SCR (bbl/min) vs.

Pressure (psi) and calculate the kill mud weight MW.

Kill Mud Weight, KMW = MW + [SIDPP/0.052 TVD @ Csg shoe](2.7)

Table12.Mud Data(the author's own work)

Pressure loss in the choke line Plot SCR, bbl/min

Figure2.17Plot SCR vs. Choke line Pressure Loss(the author's own work)

By depending on the curve of plot SCR vs. Pressure loss from the mud circulation rate we

choose the true pressure loss in the choke line

9. TableTable13. Choke line pressure loss(the author's own work)

43

The choke line effects has an effect in the Offshore drilling, the effect of the choke

line has in the Onshore drilling industry, then in the last thesis well data example we

have to calculate :

Offshore drilling ( including choke effect)

MAASP = 40 Kg/cm2

Kick Tolerance Volume = 46 bbl

OnShore drilling ( with out choke effect)

MAASP = 75 Kg/cm2

Kick Tolerance Volume = 155 bbl

2.8 The calculations of Kick Tolerance of the Thesis Well- Example 2

For Example 2there are some of different data of the thesis well, we can consider these data,

the data of Thesis Well 2 and some changing in theDrill pipe and Bottom Hole Assembly like

Drill collar and heavy weight drill pipe with the change of their diameters or length and also

using Thesis Well 2 as a sample consider the deep disscussion of different situationsof

investigation of casing shoe of determination into the Kick Tolerance, therefore. I used thesis

Well 2with the differents measured units.

The topic objectives of this point is to introduce to the some parameters and the applications

of the same parameters for calculating others which we need to learn about kick tolerance and

to plot others parameters vs. the kick tolerance as well as for rich the thesis by best

conclusions depending on two well samples.

ee

44

19Figure2.18 Thesis Well Example 2– Construction(the author's own work)

Thesis Well Data- Example 2

Units

Parameters Units

Length ft

Mud weight/ LOT ppg

Formation Pressure ppg

Influx Density ppg

Kick Intensity ppg

tepreature Fehranhitedgree F

Table14(the author's own work)

Influx Type is Gas and the gas type is Methan CH4

Le tus to introduce to the well Profile

Casing Shoe Data

Parameters Values

Shoe Depth TVD 2000

Shoe Depth MD 2000

Inclination 0

LOT 15.00

MAASP 623

Safety Margin 100

Tempreature 130

10Table15(the author's own work)

45

11. TableKick Zone DataTable

Parameters Values

Hole Size 81/2”

Kick Zone TVD 4000

Kick Zone MD 4000

Inclination 0

Tempreature 180

Mud Weight 9

Formation Pressure 10

Influx Density 0.5515

Influx Density at KickZone 0.7274

Table16(the author's own work)

Drill String Data

Drill pipe 5” OD 3850 ft Length

Drill Pipe 5” OD 10 ft Length Consider Heavy Weight drill pipe

Drill collar 61/2” OD 400 ft Length

Drill collar 61/2” OD 10 ft Length

Calculate Kick Tolerance (KT)

Kick Tolerance (KT) = 25.00 bbl

Maximum Drilling Depth Data

Required Kick Tolerance 20 bbl

Kick Tolerance Intensity 0.73 ppg

Formation Pressure 9.73 ppg

Tempreature Gradient below shoe 2.50 deg F/ 100ft

Calculate Max.Drilling Depth (MDD) TVD, Max.Measured Drilling Depth MD, Kick

Tolerance

MDD (TVD) = 4287 ft

MDD (MD) = 4287 ft

KT = 15.00 bbl

Sensitiviy Analysis Data

46

Required Kick tolerance 20.00 bbl

Minimum Formation pressure 8.35 ppg

Sensitive analyses to examin relationship between kick tolerance and well integrity.

Annular pressure of a trapped fluid in excess of annular hydrostatic pressure is caused by the

presence of an isolated fluid in a sealed annulus (annuli). When the well is heated up

becauseof further drilling or producing events, the fluid tends to expand. Also, a mechanical

response occurs from the surrounding casing walls. Onshore operations that are exposed to

the complex HP/HT loading conditions of trapped annular pressure, jack ups, and spar-type

wells allow access to any annulus; therefore, excess pressure can be easily mitigated by

bleeding it off. However, in subsea well scenarios, except for the production annulus, other

outer annuli do not allow the release of pressure. To help prevent or mitigate the possible

occurrence of trapped annular pressure in annuli, casing-connection failure, as well as

potential wellhead failure problems during the well service life, sensitivity analysis for the

drilling, completion, and production operations is performed before operations begin.

Kick Tolerance (KT) vs. Leak Off-Test (LOT) Formation Pressure (Pf)

20Figure2.19(the author's own work)

47

In Figure2.19 Shows the situations analysis of however the the leak-off test is going to

increase the kick tolerance volume will increase too if the formation pressure is constant,then

we will get more than 20 bbls volume of influx,so above the bold black line therfore

according to the sensetive analysis of kick tolerance and well integrity it will give the failur

result of casing seat selection or connection because the required kick tolerance is 2o bbls,

therfore after the plot of the correct data of well , at the 10 ppg formation pressure and 20 bbls

kick tolerance interception the Lot will be 14.3 ppg which is the true value of the same

situations.

KickTolerance vs. Formation Pressure,FP (LOT)

Figure2.20(the author's own work)

In the Figure2.20 we can explain that the situation considers the checking for the result of the

Figure 2.19, then during the interception between the required kick tolerance 20 bbls and the

value of Leak-off test which was 14.3 ppg in the Figure2.19 we will get the value of

formation pressure 10 ppg.

48

Kick Tolerance Vs. Formation Pressure (FP)

21Figure2.21(the author's own work)

In Figure2.21 We mentioned that however the formation pressure is going to decrease with 15

ppg LOT the kick tolerance will increase compare with the required volume and the inversly

with increasing the formation pressure with same value of LOT the kick tolerance will

decrease compare with the required volume which was 20 bbls and the kick intensity

willdecrease also.

49

2.9Kick Identification Chart

During the drilling phase it is possible to identify the influx type in case of High Pressure

High Tempreture HPHT wells, gas could be in a liquid state until it reaches the bubble point,

therefore the gas detection in mpre difficult.

22Figure2.22 Kick Identification Chart

Then, by calculate the Maximum Pressure Gradient PGmax or IG from the equation

IG = MW – 10 × (SICPP – SIDPP) / H i (2.7)

IG = Influx gradient, psi/ft

MW = Mud weight, PPg

SICPP = Shut in casing pipe pressure, psi

SIDPP = Shut in drill pipe pressure, psi

Hi = Height of influx, ft

To know the value of Influx Gradient, IG, psi/ft and using the kick identification chart we can

introduce to the type of Kick or Influx.

2.10 Kick Circulation with Driller’s or Wait and Weight method

Knowing pit gain and SIDPP, the same diagram used int he planning phase, allows to estimate

if or kick volume can be directed out or bulhead back immediately into formation avoiding

potential underground blowout phenomena.

50

23Figure2.23 Kick Circulation with driller’s or wait and weight method

51

3.Conclusions

The conclusions which I reached during the working on my thesis are:

I investigated the importance of kick tolerance and well integrity considering with safe

well planning is.To investigate importance of kick tolerance and well integrity

considering with safe well planning is the assumption that the fracture gradient is

lowest at the previous casing shoe is not necessarily true; fracture gradients vary with

the in-situ stresses (overburden, pore pressure, etc) superimposed tectonic stresses and

formation type. Hence the lowest fracture gradient in an open hole section is not

always found at the previous casing shoe. This can have severe implications for the

well control practice and casing setting depth, therfore the key factors to determine the

depth of casing seat are Pore Pressure, Fracturing Pressure and Kick Tolerance.

Casing seat selection must be designed using the limited kick method (Realistic Well

Design, Enough Safe, Not Expensive the Well Construction), so for different wells

realistic kick size should be assumed early kick detection , Mud logging , Shut the

well in the time (Hard shut-in) and well control drill.

I described the theoretical background of kick tolerance than a key element of casing

shoe depth determination my result is the kick tolerance is an important concept that

can be applied both in drilling operations and in casing program design.

Applications of Kick Tolerance concept are especially helpful in wells currently by oil

and gas industry, for which more complex planning execution is required.Considering

kick tolerance made drilling execution safer and more economical by reducing the

probability to have an incident.

I Introduced the theoretical and practical methods that are usable to determine the

formation integrity is that the main reason for performing the formation integrity test

(FIT) are:

1. To determine the fracture gradient around the casing shoe and therefore establish

the upper limit of the primary well control for the open hole section below the

current casing.

52

2. To investigate well bore capability to withstand pressure below the casing shoe in

order to validate or invalidate the well engineering plan regarding the casing shoe

setting depth.

3. In practice introduction I got that an accurate evaluation of a casing cement job as

well as of the formation is extremely important during the drilling of a well and for

subsequent work.

I determineda theoretical well data to perform sensitive analyses to examine relationship

between kick tolerance and well integrity.

I made the sensitive analyses Kick Tolerance (KT) vs. Leak Off-Test (LOT) and Formation

Pressure (Pf) and Kick Tolerance Vs. Formation Pressure (FP).

The sensitive analysis show that the the leak-off test is going to increase the kick tolerance

volume will increase too if the formation pressure is constant, then we will get more than 20

bbls volume of influx, in the given situation according to the sensetive analysis of kick

tolerance and well integrity it will give the failur result of casing seat selection or connection

because the required kick tolerance is 2o bbls, therfore after the plot of the correct data of

well, at the 10 ppg formation pressure and 20 bbls kick tolerance interception the Lot will be

14.3 ppg which is the true value of the same situations.

I determined for the given well the safe casing shoe depth that is acceptable the required well

integrity there may be many causes of sustained casing pressure. Through the well integrity

survey performed by the Petroleum Safety Authorities, the most common causes for SCP are

related to deficiency in cement and casing. The best way of eliminating influx of formation

fluid from formations along the wellbore is to identify them in the initial well design planning

and when cementing, make sure the annulus is properly cemented. And I want to give some

indicators in my thesis that also consider the important factors of the main subjects of the

thesis are:

During Planning

We estimate formation strength, pore pressure, gas gradient including casing strength and

BOP rating. A diagram can be used in order to verify if planned casing setting depth and mud

weight are suitable to ensure the minimum kick tolerance requirements.

During Drilling

53

After Leak-off Test we only know the formation strength at shoe depth (TVD), we try to

measure pore pressure and we know what mud weight we can use. Knowing pit gain also and

shut in drill pipe presure (SIDPP), the same diagram allows to estimate if or kick volume can

be circulate out or bullhead back immediately into formation avoiding potential underground

blowout phenomena.

During Gas Circulation

Determine the Maximum Allowable Annular Shut-In pressure MAASP value depending ont

he gas position int he annulus taking into consideration the uncertainties.

54

References

1. H. Rabia: Oilwell Drilling Engineering Principles and Practice Graham Tratman Ltd.

London 1995. 322 p.

2. Hubbert, M. and Willis, D. (1957). “Mechanics of hydraulic

fracturing”.Trans.Am.Inst. Min. Engrs, 210, 153-68.

3. Dr. Imre Federer: The kick tolerance is one of the significant factor for determination

of casing shoe depth. XXVII. OMBKE International Conference, Siófok,16-19 of

Sept. 2008.

4. Eni S.p.A. Exploration & Production Division. Via Emilia, 1. 20097 San Donato

Milanese (Milan) Italy inside manual.

Literature

1. Jaeger, JC, Cook NGW (1979). “Fundamentals of Rock Mechanics”.

Chapman and Hall

2. Benham, P. and Warnock, F. (1973). “Mechanics of Solids and Structures”.

Pitman,London.

3. Matthews, W. and Kelly, J. (1967). “How to predict formation pressure and

fracturegradient”. Oil and Gas Journal, February, 92-106.

4. Marsden, R (1999). Rock mechanics course notes For Entrac Consulting.

5. Pilkington, P.E. (1978). “Fracture gradient estimates in tertiary basins”.

PetroleumEngineer, May, 138-148.

6. Eaton, B.A. (1969). “Fracture gradient prediction and interpretation of hydraulic

fracturetreatments”. Journal of Petroleum Technology, October, 21-29.

7. Christman, S.A. (1973). “Offshore fracture gradients”. Journal of Petroleum

Technology,August,.910-914.

8. Haimson, B. and Fairhurst, C. (1967). “Initiation and extension of hydraulic fractures

inrocks”. Society of Petroleum Engineers Journal, September, 310-311.

9. Bradley, W.B. (1979). “Failure of inclined boreholes”. Transactions of the

ASME,December, 101, 232-239.

10. Hoek,E and Brown E T (1980). “Underground excavation in rock”. Institution

of.Miningand Metallurgy

55

11. McLean, H R and Addis, MA.(1990). “Wellbore stability: the effect of strength

criteriaon mud weight”. SPE Annul Conference, Sept.

12. Snyder, R. and Suman, G. (1978, 1979). “World Oil’s Handbook of High Pressure

WellCompletions”. World Oil.

13. Exlog Applications Manual (various prints) “Theory and evaluation

of formationPressures” Exploration Logging Inc.

14. Jordan J.R and Shirley O.J (1966)“Application of drilling performance data

tooverpressure detection” JPT.

15. Rehm B and McClendon R (1971) “Measurement of formation pressures from

drillingdata” SPE 3601, AIME Annual Fall Meeting, New Orleans.

16. Snyder, R. and Suman G (1978, 1979) “World Oil's Handbook of High Pressure

WellCompletions World Oil”.

17. Schlumberger (1972).“Log Interpretation Principles”.Vol 1.Schlumberger Publication.

18. Fertl W.H. (1976) “Abnormal Formation Pressures”. Elsevier, Amsterdam.

19. Rosland, H. A., Effendhy, E., and Park, S. J. 2013. HPHT Well Basis of

Design CaseStudy: Offshore Thailand Advanced Tubular Analyses Experience. Paper

IPTC 17104presented at the International Petroleum Technology Conference, Beijing,

China, 26–28 March. 20.Mitchell, R. A. and Sweatman, R., 2013. Wellbore Stability

and Integrity Contributors Revealed by Thermal Modeling and Fluid Analysis. Paper

OTC 24072 presented at the Offshore Technology Conference, Houston, TX, USA,

May 6-9, 2013.