CHAPTER 3

DIRECTIONALL Y DRILLED WELLS

ANO DIRECTIONAL SURVEYS

INTRODUCTION

A directionally drilled or deviated well is defined as a well drilled at an angle less than 90 deg to the horizontal (Fig. 3-1). Wells are normally deviated intentionally in response to a predetermined plan; however, straight boles often deviate from the vertical due to bit rotation and natural deviation tendencies of subsurface formations.

The technique of controlled directional drilling began in the late 1920s on the US Pacific coast (LeRoy and LeRoy 1977). Through the use of controlled directional drilling, a wellbore is deviated along a preplanned course to intersect a subsurface target horizon(s) ata specific location (Fig. 3-2). Our primary interest in directionally drilled wells centers around their application to subsurface mapping.

APPLICATION OF DIRECTIONALLY DRILLED WELLS

There are a number of reasons to drill a directional well. Sorne of the more common applications are shown in Fig. 3-3. The most common application is the drilling of offshore wells from a single platform location [Fig. 3-3a]. The use of a single platform from which multiple wells are drilled improves economics and simplifies production facilities.

- Onshore, wells are commonly deviated due to inaccessibility to the surface location directly over the subsurface target. Buildings, towns, cities, rivers, and mountains are the kinds of surface obstructions that require the drilling of a deviated well.

One very important safety application of a deviated well is the drilling of a relief

21

22 Chap. 3 / Directionally Drilled Wells and Directional Surveys

well to kill a well that has blown out [Fig. 3-3(f)]. There are other applications of deviated wells, but they are beyond the scope of this textbook and are not discussed.

COMMON TYPES OF DIRECTIONALL Y DRILLED WELLS

There are many complex factors that go into the design of a directionally drilled well; however, most deviated wells fall into one of two types. The most common type is a simple ramp well [Fig. 3-l(a)], sometimes called an "L" shaped hole. These wells are drilled vertically to a predetermined depth and then deviated to a certain angle which is usually held constant to total depth (TD) of the well. Many wells are drilled with an "S" shaped design. With an "S" shaped hole, the well begins as a vertical hole and then builds to a predetermined angle, maintains this angle to a designated depth and then the angle is lowered again, often going back to vertical [Fig. 3-l(b)].

General Terminology

The terms used to describe various aspects of a directionally drilled well are defined here and illustrated in Fig. 3-1.

SIMPLE RAMP WELL

l SURfACE o·--------

1000'

2000'

3000'

4000'

5000'

KOP • 1000' MO, 1000' TVD

ANGLE MAOE 202' TVO, 2$00'MO

HORIZONTAL 015 TANCE 316'

KICK

(a)

TO 5000' TVO 5465' MO

Figure 3-1 Diagrammatic cross section illustra­tion (a) a simple ramp or "L" shaped well, and (b) a more complicated "S" shaped well. (Published by permission of Tenneco Oil Company.)

Common Types of Directionally Drilled Wells

"s• SHAPE WELL

O' SUUACE

1000' KOP • 1000' MO, 1000' TVD

3000'

4000'

SOOO'

6000' J&b' 1

1

1 1 1

KICK@ I OROPPOINT 886 ' I ... ·-----·.il

KICK@~ 1399'

ANGLE OROP POIN T 329&' 1VD, 3500' MO

DROP RATE l-l/2•/1001

-VERTICAL POIN T S201' tvo, SSOO' MO

---10 6000' TVO 6292'MD

(b)

Figure 3·1 ( contlnued)

rHORIZONTAL PLAN

Figure 3·2 Block dlagram showing the vertical and horizontal plan vlews of a di· rectlonally drilled well to a predeterminad subsurface target. (Published by permission of Eastman Christensen.)

23

24

(a} (b}

Chap. 3 I Directionally Drilled Wells and Directional Surveys

(e) (d} (e) (f} (g} (h, i, j} Figure 3·3 Applications of directional drilling. (a) Multiple we!!s offshore ·or from artificial islands. (b) Shoreline drilling. (c) Fault control. (d) lnaccessible location. (e) Stratigraphic trap .. (f) Relíef well control. (g) Straightening hole and side tracking. (h. i, j) Saltdome drilling. (From LeRoy and LeRoy 1977. Published by permission of the Colorado School of Mines.)

KOP = Kick-off Point = Depth of initial deviation frorn vertical rneasured as rneasured depth (MD), true. vertical depth (TVD), or subsea true ver-tical depth (SSTVD). .

Build Rate = Build Angle = Rate at which the angle changes during deviation. It is usually expressed in degrees per 100 ft drilled . Exarnple: 2 deg per 100 ft.

Rarnp Angle = Hold Angle, Drift Angle, Angle of Deviation = Angle frorn the vertical that a well rnaintains frorn the end of the build through the rarnp segment of the well.

BHL = Bottorn Hole Location = Horizontal and vertical coordinates to the total depth point usually rneasured frorn the surface location.

Drop Rate = Rate at which the rarnp angle changes in degrees per 100 ft. Measured in "S" shaped holes.

Vertical Point = The depth where the we11 is back to vertical rneasured as MD, TVD, or SSTVD.

DIRECTIONAL WELL PLAN

A variety of data go into the design of a directionally drilled well, including the depth and distance frorn the surface location to each subsurface target, diarneter of the target, kick-off point, build rate, platform location, lease lines, hole size, and total depth of the well. Once prelirninary studies indicate the need for a deviated well, rnost cornpanies rely on a directional drilling service cornpany to prepare the final directional plan.

A directional well design consists of both vertical and horizontal plans. Figure 3-4 shows the horizontal and vertical plans for the Diarnond Sharnrock Well No. 1 in West Carneron Block 75 offshore Gulf of Mexico. Reviewing Fig. 3-4a, we see that the kick­off point for this well is about 950 ft rneasured depth (MD), and the build rate averages about 2 deg per 100 ft to a maxirnurn deviation angle of 45º30' at a rneasured depth of 4800 ft. Figure 3-4b shows the horizontal plan for the well . The plane of the proposed direction is south 46 deg 25 rnin west frorn the surface location with the bottorn hole location (BHL) 10,872 ft frorn the surface location. The well is drilled to a rneasured depth of 19,484 ft , which is equal to a true vertical depth of 15,695 ft.

Directional Well Plan 25

OIAMONO SHAMROCK OCS-G-5276 WELL NO . 1 WEST CAMERON BLOCK 75

OIAMONO -SHAMROCK OCS- G-5276 WELL NO. 1 WEST CAMERON BLOCK 75

PLANE OF PROPOSAL S46º25'W

PLANE OF PROPOSAL s 46º 25' w

VERTICAL SECTION SCALE: 1" = 4000'

0°0 ' EAST GRIO

HORIZONTAL PLAN SCALE: 1" = 2000'

OºO' EAST GRIO

8000 7000 6000 5000 4000 3000 2000 1 000 o \ 000 , 1 , 1 1 t 1 1 1 S/L 1

100 - 100· '4)

-900' ..,

~~~~~~~~~~~~~~-:1j)100 ' MO

-1749 ' \JO -1000

4000 - -2000

-JOOO

8000 - -4000

-5000

-6000

-7000

15695 - '===='=08::;n::::· ====~ u~e .. 1«> s 46º 25' w

B.H .L. 10873 ' S-47° 12 ' 07" W S- 7386 . 19'. W-7976.55 ' T.V.O . -1 5695'

-8000

o 1

4000 8000 12000 M.O. -19484 '

(a) (b) Figure 3.4 (a) Vertical section plan for a directional well. (b) Horizontal plan for the same directional well shown in Fig. 3-4a. (Published by permission of Gardes Direc­tional Drilling.)

Figure 3-5 illustrates the vertical plan for a well that has a maximum deviation angle of 94 deg anda maximum build angle of 14 deg per 100 ft. The wellbore starts out vertical, and at a depth of 1659 ft (TVD) it is horizontal. Such wells are not commonly drilled ; however, with technique and equipment advances, high angle wells (60 deg-80 deg) are becoming more common. A well such as the one shown in Fig. 3-5 is referred to as a horizontal wellbore. Lateral (horizontal) drilling is used for various purposes, including (1) to parallel low permeability sand beds to maximize production; (2) to restrict unwanted water flow; and (3) to optimize drilling in coal seam methane operations.

Commonly, deviated wells are drilled with a build rate of 2 deg per 100 ft of hole drilled . Figure 3-6 shows the scaled chart for a 2 deg per 100 ft build rate. Such charts are used to make a quick estímate of well design after structure maps have been made on target horizons. For example, from the chart, a target horizon located at a TVD of 10,000 ft and a horizontal distance of 4000 ft from the platform location requires the drilling of a well with a deviation angle of approximately 23 deg to a measured depth of 10,800 ft. Such charts are available from directional service companies ranging in build rate from 1 deg to 5 deg per 100 ft.

26 Chap. 3 / Directionally Drilled Wells and Directional Surveys

HOAWELL ENEAOY OllLON KEIRS WELL NO . 1 PINE l8LANO f IELO MIXON RIO 1

VERTICAL PLAN SCALE l'•!SOO.o ·

o

~o

eoo e .. Q • o

• !: 1000 .. L ~ >

• ~ L ..

11100

2000

N

-~ •º 30'EAST

TRUE

1 1 1000 1~00

vertical S1ct>on

11/29/ 88

2060 2ebo

Figure 3·5 Vertical plan for a nearly horizontal wefl with a maximum deviation angle of 94 deg. (Published by permission of Gardes Directlonal Drilling.)

DIRECTIONAL TOOLS USED FOR MEASUREMENTS

The tools that are used to survey directionally drilled wells fall into two categories: magnetic and nonmagnetic.

Magnetlc Surveys

Magnetic is a generic term used to describe severa) surveying methods which use a magnetic compass for dir~ction and therefore must be run inside a special nonmagnetic drill collar to negate the effects of the drill pipe. An example of such a survey is the "single shot" magnetic survey. This device records on a heat-resistant film disc the magnetic direction and inclination angle of the wellbore at specific depth intervals. A ''multi-shot'' survey uses a film strip to record severa! readings of hole angle and direction at different depth intervals.

Nonmagnetic Surveys

A nonmagnetic survey, sometimes referrcd to as a drift indicator or Totco, is usually run in vertical or nearly vertical wells where directionaJ information is not required. This tool generally consists of a housing or barrel. a motion indicator. a timer, a punch, and a

I f­a.. w o ..J <{ (.)

f­a: w > w ::> a: f-

UNIFORM 2º00' INCREASE IN DRIFT PEA 100 FT OF HOLE DRILLED

o· ...i.."" : , · 1 l 1

1

3,000

t=..!r. 11' l i 11 ~· 1 1 1 1

1 i l

t M , f 1 '

Pl 1 ; 1 1 ., :\(]•~ i · 1- -''-+_,_-'_,'-+.~

-.~ ' I , 1 \ 11~\ :¡, N 1 1 1 ~ .\ ~ \\\\'\'t\' ~ ~ ~ 1 1

MEASUREO VERTICAL OEV1ATl0tl 0€PTH OEPTH

0 .00 100.00 200.00 300.00 •00.00

500.00 600.00 700.00 800.00 900.00

1000.00 1100.00 1200.00 1300.00 1400.00

0.00 99.98

199.M 299.•5 398.70

497.'7 595.62 693.06 789.64 885.27

97982 1073.17 1165.21 1255.8' 1344.94

O.DO 1.75 6.98

15.69 27.Ba

43.52 62.60 85.10

110.98 U0.21

172.77 208.60 247.67 289.93 335.33

ORIFT

o·oo· 2·00· 4•00 · 6'00 ' 8'00'

10'00' 12·00· 14'00' 16'00' 18'00 '

20'00 ' 22·00 · 24'00 ' 26'00 ' 28'00'

llEASUREO VERTICAL lfV1AllON ORITT OEPTH OEPTH

1500.00 1600.00 1700.00 1800.00 1900.00

2000.00 2100.00 2200.00 2300.00 2400.00

2500.00 2600.00 2700.00 2800.00 2900.00

3000.00

1432 39 1518. 11 1601.97 1683.88 1763.7'

1841.45 1916.92 1990.05 2060.76 2128.95

2194.56 2257.48 2317.66 2375.02 2429.'8

2480.98

383.81 30•00· 435.31 32·00· 489. 11 3' ·oo · 5'7.13 36'00' 607.30 38 ·oo · 610.23 40·00· 735.8' •2 ·oc· 804.03 "'00 . 874.74 46'00' 947.87 48 ·oo ·

1023.3' 50 '00. 1101.05 52'00' 1180.91 54 ·oo· 1262.82 56'00 ' 13'&.68 ss ·oo · 1432.39 60 '00.

\ 1 1 \ \ \ '\ ,~ '><~'\."-~ ~"- , ¡-~ ~ ...--- · ' j · H -+-1h-- --.1 -+-41-+--'-H-t--t-+-H 1 \1 \\\\1\ \\'\\\'-~~~ :--.. ' i . . 1 1 1 ill ! i

1 1 \ '·"JI', 10~~' <..: ,......_-..__: ··-t---o • - · ~ ...,..... 1 ~ ,. t-.-+- 1'-·- +-1 H-H1 --t-+-H-+-+-i 4 ,000'1-tt-t+-tttlf-T-\l-':f~?.1~~\ •~V~~~\~l,~\\;'~:'\.~,~-~,~~~,~,?....._..at~.':-....-f-t--+--..._;¡~-++-r--t,~+-;..__¡_..+-+_;~__¡__¡_j...41-i.~1-i._¡_+-J_¡_-J-~

' ~\ \ \ '\ \,'\.:\. " '-~ '1'-......"'-... 1 i ! 1 1 i .1

7,000

10,000

12,000

13,000

14,000

l 1

1 ' il '\ :n1 'l/ ' \ I'\ \ \ , '\ ) ('\. '- "" !"-1 . \ \ l ·- 1:.(l .Al" i\ , '\ 1 . \ 1 X ' \..i ~ / :'

H-1!--++-+1-++H-, --11-t-~t+,41\-.-~-+.\l'lc--tld-,~./'°-b~+-~ . ...µ\-t-- \ 1 '\ '\ V .\ '\ I'\ / ' . '-1 1 1 re;; ' , . 1 · ~ !'\ \ iv \ , , ' " 7' '-! 1

.... / / '-

i 1 11 J!.-- \ : \ 1 1\ \ 1 \ \ 1 .x •\ '\ 1 " ; '{

~=t::t:~m::n~l:!L--jHj:flt:\t\=ttt::::'t:::'t~\ . il___. \ ¡ . l '\ '\ l\. '\ ·'- '/ \, != 1 1, \ 1 \ . \ · \!\ · Y1 1 '\ i " -'-'b.4-!/'l...;"~-+...;"~+-l!'....~' +..;rv~~-+"--l 1 1 1 \ \ . ' • •~ .X 1 \! 'l I'\ )( l ' '-

1 1

l 1

1 '

1 ' 1 1 1 1 1 1 1 1

; · 1 \ .'° 1 , 1 , ' \ 't \ \ f / \ : 1 I'\ ,, !'-. 1 - 1 ~ . \ \ 1 \ '\ ./ \ )< " "

1 \ 1 \ \ ·~ "' '.:.--1\ . \ \ '\ ,.,. \. 1 1 i ' \ ..... ...-·\ l 'I \- \ \ \,.., ' 1

, 1 1 1 1 · ...- 1 'I · 1\ 1\ \ V \ 1 11 i:; 1 \ : 1\ 1 1 • ,) '\! r\:

1 \ • u- ' ' \l :i.t' · :'\ \ ~ ~ i\ \ . 1 1 ' \ \ 1 \ ' ,,, 1\ 1 l '

\ \1 \ • \ \ ! > \V. ~ \ 'I f · \J :¡ 11 1 \ \ ,<;¡IJ - \ \ i \ \ l'\

I'\

\ 1 \ 1 1 \ -1'" \ '\ \ l \ 1 1 1 1 ..l 1\ .

1 1 1 1 \"" 1 \1 1

1 ___ , \ ~1\

\.._ "" "' f ' I'. rt

1 H"

l \ . 1 1 1 ' 1 \ 1 11 1 1 1\ 1 'I

1\ 1\ 1 \ 1

\

' '\ l

' ''\

\

'\

' '

'\I 1\.

54º

52'

500

48°

44°

42°

40º

15,000 2' 4º O' 1.000·

6' 9•· 2,000'

10' 12° 3,000'

14º 16" 4,ooo:

10· 20° 5,000'

22' 24' 6,000'

26' 7,000'

28' 30' 8,000'

32' 9,000'

34° 36' 10,000'

38º 11,000'

HORIZONTAL DEVIATION

Figure 3-6 Scaled chart for a build rate of 2 deg per 100 ft of hole drilled. (Published by permission of Eastman Christensen.)

27

28 Chap. 3 .' Directionally Drilled Wells and Directional Surveys

Figure 3·7 Example of a Totco survey. Well deviation angle 4.5 deg.

printed paper disc. The unit is either run on a wire line or dropped on a drill bit. When the motion sensor determines that the tool is no longer moving, the timer is activated, and after a predetermined Jength of time the punch is released. The punch, which is allowed to swing freely and act as a plumb bob, drops vertically and punches a hole in the paper disc, which is marked in degrees. Figure 3-7 shows a Totco disc scaled to a maximum of 8 deg. The hole punched in the Totco indicates that the well in which it was taken was at an inclination angle of 4.5 deg.

One of the newer surveys is called a Gyroscopic Survey. Because the magnetic compass is replaced by a gyro compass disc, the system can be run in both cased and noncased holes. The gyro system can be set up as a single or multi-shot instrument.

DIRECTIONAL SURVEV CALCULATIONS

There are a number of methods which have been developed to calculate the directional survey for a deviated well. These methods include (1) tangential, (2) trapezoidal, (3) average ang]e, (4) mínimum curvature. and (5) radius of curvature. These methods are used to calculate the three-dimensional location of a directional wellbore anywhere along its entire length.

Three measurements go into the directional survey: (1) measured depth, (2) deviation angle , and (3) direction of deviation. These measurements taken at specific depth intervals are used to calculate the directional survey of a well. Figure 3-8 shows a portion of the

Directional Survey Calculations 29

DIRECTIONAL SURVEY

<l) C2l (3) (4) (5) (6) (7) (8) (9)

TRUE T O T A L OOG LEG SOJBSEA MEAS . VERTICAL DRIFT ORlFT VERTICAL R E C T A N G U L A R CLOSURES SEVERln ::JEPTH DEPTH DEPTH ANGLE DlREC SECTlON C O O R O l N A T E S OlSTANCE OIRECT OEG/lOOF1 i'EET FEET FEET o t1 o " FEET FEET FEET FEET ll M

5299.88 5700 S330.88 31 30 N 37 O E 1490.00 1390 . 73 N S38 . 16 E 1491.22 N 21 9 E 1.04 S385. 14 S800 S416.14 31 30 N 32 O E 1S41 .27 1433. 77 N S67.7S E 1S42.09 N 21 36 E 2.61 5470.52 S900 sso1.52 31 15 N 25 O E 1S93° lO 1479.SO N S92.S7 E 1S93.76 N 21 SO E 3°6S S~56.0l 6000 SS87.0l 31 lS N 20 O E 1644.95 1S27.41 N 612.42 E 1645 . 61 N 21 S 1 E 2.s9 5641.9S 6100 S672.9S 30 lS N 14 O E 1695.73 1S76.28 N 627.36 E 1696.S4 N 21 42 E 3,23

S/28.23 6200 S7S9.23 30 30 N 10 O E 174S.28 162S.73 N 637.87 E 1746.39 N 21 25 E 2.04 S8!4.50 6300 S84S.50 30 lS N 8 O E 1794. 24 1675.67 N 64S.78 E 1795.81 N 21 5 E 1.04 5000.88 6400 5931 .88 30 IS N 8 O E 1842.79 1725.S6 N 652.79 E 1844.91 N 20 43 E o .oo 5?87.S9 6500 6018.59 29 30 N 10 O E 1891 .02 1774.76 N 660.S9 E 1893.71 N 20 25 E 1.2s 6075.26 6600 6106.26 28 o N 12 O E 1937.98 1821.97 N 669.76 E 1941. 17 N 20 11 E ¡, 78

ói~4.16 6700 6195.16 26 30 N 12 O E 1982.85 1866.7S N 679 . 28 E 1986,50 N 19 60 E 1. so 6:54.:3 6800 628S.23 25 o N 13 O E 202s.50 1909.17 N 688 .68 E 2029.58 N !9 so E 1.56 6'.'ª'·86 6900 637S.86 2S o N 16 O E 2067.24 19S0.08 N 699.26 E 2071 .66 N 19 44 E 1.21 o~:?S . 40 7000 6466.40 2S lS N 18 O E 2109.<:3 1990.68 N 711 .68 E 2114.07 N 19 40 E o.89 6~:5.75 7100 6556. 75 2S 30 N 20 O E 21s:. :s 2031 .20 N 72S .63 E 2156 .92 N 19 40 E o . 89

66 16.10 7200 6647. 1 o 2S lS N 20 O E 2194.92 2071.47 N 740.29 E 2199 .77 N 19 40 E o.2s 6706.73 7300 6737.73 24 4S N 20 O E 2237.tl 2111.18 N 7S4 . 74 E 2242.03 N 19 40 E o.so 6797.82 7400 6828.82 24 o N 20 O E 2278.30 2149.96 N 768.86 E 2283.30 N 19 41 E o. 7S 6889.17 7SOO 6920.17 24 o N 20 o E 2318.90 2188.18 N 782. 77 E 2323.98 N 19 41 E o.oo 6980.53 7600 7011.53 24 o N 20 O E 2359.50 2226.40 N 796.68 E 2364.6S N 19 41 E o.oo

Radlus oí Curvature Calculation

Figure 3·8 Part of the directional su rvey for a deviated well. (Published by permission of Gardes Directional Drilling.)

directional survey from a deviated well. The tabular printout for this directional survey has nine separate columns of data for each survey point in the well.

Co/umn

1 2 3 4 5 6

7

8

9

Data

Subsea depth of wellbore in feet Measured depth of wellbore in feet True vertical depth of wellbore in feet Angle of wellbore deviation Direction of wellbore (true bearing) Distance in feet from the surface location along the pro·

posed directional path True bearing and distance of each survey point from the

surface location in rectangu lar coordinates True bearing and distance from surface locat ion directly to

each survey point Maximum change in hole angla in degrees per 100 ft .

lf the cased or surface section of the hole was surveyed with a nonmagnetic survey such as a Totco, the angle of the cased portion of the hole will be displayed on the survey along with an estimate of the maximum possible deviation of this portian of the hole, as shown in Fig. 3-9. The 146.75 ft highlighted on the survey indicate that if the wellbore drift in the cased portiÓn of the hole was all in the same direction, the well at a depth of 3513 ft could be up to a maximum of 146. 75 ft from the surface location. Notice at the end of the survey that it indicates that the bottom of the hole lies within a circle of

30

MEASURED DEPTH

1000.00 2000.00 3000.00 3513 .óo

4000.00 4500.00 5000.00 5500.00 6000.00 6500. 00 7000.00 7500.00 8000.00 9500.00 9000,00 9500,00

10000.00 10500.00 11000.00 11500.00 12000.00 12500.00 13000.00 13500.00 13700.00

Chap. 3 I Directionally Drilled Wells and Directional Surveys

DIRECTIONAL SURVEY DATA BAYOU FER BLANC FIELD, LAFOURCHE REALTY CO. WELL NO. B-3

DRIFT TVD COURSE DEVIATION COURSE COORDINATES TOTAL COORDINATES ANGLE DEPTH ~ DIRECTION ~ ~ EAST WEST NORTH SOUTH EAST WEST

1-45 999.53 30 . 54 CASING 2-30 1998,58 43.62 CASING 2-45 2997.43 47.98 CASING 2-45 3509.84 24.61 CASING

MAXIMUM POSSIBLE DEVIATION OF CASED HOLE AT THIS POINT IS 146 . 75 FEET.

2- o 3996 . 54 17,00 s 39 w o. 13 . 21 o. 10, 70 o. 13.21 o. 10,70 1- o 4496. 47 8 . 73 S 36 E o. 7.06 5 . 13 o. O, 20.27 o. 5.57 0-30 4996 , 45 4.36 N 82 E 0.61 o. 4 . 32 o. o. 19.66 o. l. 25 0-30 5496.43 4.36 s 64 w o. l. 91 o. 3 .92 o. 21.57 o. 5.17 0-45 5996,39 6.54 s 26 w o. 5.88 o. 2.87 o. 27.46 o. 8 . 04 1- o 6496.31 8.73 s 20 w o. 8.20 o. 2.98 o. 35.66 o. 11.02 1- o 6996.23 8 . 73 s 85 w o. 0.76 o. 8.69 o. 36.42 o. 19. 71 1-15 7496.ll 10.91 s 77 w o. 2 . 45 o. 10.63 o. 38 . 87 o. 30.34 2- o 7995 . 81 17,45 s 24 w o. 15 . 94 o. 7,10 o. 54 .81 o. 37.44 2- o 9495.73 9.33 s 30 w o. o. o. 3.00 o. 30.45 o. 45.00 1-45 8995,50 15 .27 s 25 w o. 13.84 o. 6.45 o. 64. 29 o. 51. 45 2-15 9495,ll 19.63 s 33 w o. 16.46 o. 10.69 o. 80.75 o. 62 .14 2-30 9994.64 21. 81 s 58 w o. 11. 56 o. 18.50 o. 92 . 31 o. 80.64 1-45 10494,41 15.27 s 75 w o. 3,95 o. 14 . 75 o. 96.26 c. 95.39 2-30 10993,93 21,81 N 85 W 1.90 o. o. 21.73 o. 94.36 c. 117 .11 1-45 11493. 70 15.27 s 75 w o. 3.95 o. 14.75 o. 98.31 c. 131. 86 2- o 11993 . 39 17 . 45 N 38 W 13.75 o. o. 10.74 o. 84 . 56 c. 142.60 2- o 12493.09 17.45 s 40 w o. 13.37 o. 11.22 o. 97.93 o. 153 . 82 2- o 12992.78 17.45 s 92 w o. 2.43 o. 17.28 o. 100.36 o. 171.10 1-30 13492.61 13 .09 N 64 W 5.74 o. o. 11, 76 o. 94.62 o. 182 . 86 1- o 13692 . 58 3 . 49 N 7 E 3.46 o. 0.43 o. o. 91.15 c. 182,44

THE BOTTO.M OF THE HOLE LIES \VITHIN A CIRCLE OF RADI US 146. 75 FEET WITH ITS CENTER LOCATED 203.94 FEET SOUTH 63 DEGREES 27 MINUTES WEST OF THE SURFACE LOCATIO~

Figure 3-9 A directional survey from a well in which the surface casing was surveyed with a Totco providing deviation angle but not direction. Notice, at 3513 ft, the max-lmum possible deviation of the cased hole is 146. 75 ft. This assumes that the wellbore deviation in this portien of the hole was in one direction.

radius 146.75 ft with its center located 203.94 ft south 63 deg 27 min. west of the surface location. Such information may be important in fault, structure, and isopach mapping (see Fíg. 7-57 in Chapter 7).

DIRECTIONAL SURVEY UNCERTAINTIES ..

The error introduced by the method of calculation becomes almost academic when the'· other directional survey uncertainties are considered. Tenneco Oil Company conducted a detailed study of directional survey uncertainties in 1980. An important conclusion from the study indicates that there is a 90% certainty that any directional well will have an error of 35 ft or less TVD and 140 ft or less in departure. This conclusion is drawn irrespective of MD, hole angle, or survey type. This means that wells with hydrocarbon contacts that vary up to 35 ft TVD may well be in the same reservoir with the variations due merely to survey error, rather than such geological events as permeability barriers or faults.

.· ... : ,_--¡ .

Directional Survey Uncertainties

VERTICAL UNCERTAINTY*

i::l

30

20

o o

100

50

<5 20 ::i:: µ. o ~ 10 µ.. o o o r:::· 5

t: +I

2

0.5

/ / V

- ;' V /

,l/

- . ./

~ ¿

t.--lo-

POOR MAG,,.. v

/

VPOOR ~

I , ~

l...--:;::'-/ L,.

/ /

V v I / y --í/ GOOO MAG V /

V V ~-··--· I/ GOOO GYRO GYRODATA ~

-1.1

vr··'I INERTIAL NAVIGATION

10 20 30 40 50 60 70 80 90

INCLINATION, DEGREES • After Wolff/deWardt

Figure 3·10 Expected vertical uncertainty in a deviated well considering various types of surveys. (Modified from Wolff and de Wardt 1981. Pub lished by permission of the Journal of Petroleum Technology and Gyrodata, lnc.)

31

The diagrams shown in Figs. 3-10 and 3-11 are modified from Wolff and DeWardt (1981). These diagrams give an indication of expected uncertainty when MD, hole angle, and survey type are taken into consideration.

Survey errors can be corrected in sorne cases in fields that have hydrocarbon/water contacts. Wells are very often " corrected" to fit the contact. This is usually done by selecting a contact that fits most of the wells and then adjusting the depth of the well(s) that does not fit . An example of how to adjust a well is shown in Fig. 3-12. The water contact in Wells No. 1 and 2 is ata depth of -9738 ft, whereas the contact in Well No. 3 is at a depth of -9748 ft. Since data from two wells are in agreement with a water contact at - 9738 ft , Well No. 3 is adjusted upward 10 ft to correct the water level from -9748 ft to -9738 ft. Not only is the water level corrected, but the structural depth of the sand (top and base) is also corrected upward 10 ft. Therefore, the top of the sand at a depth of -9720 ft becomes -9710 ft. An understanding of directional survey errors can at times eliminate the need for a "production fault" to explain discrepancies in water levels.

-9700

-9710

-9720

-9730

-9740

-9750

-9760

-9770

32

LATERAL UNCERTAINTY* 300 ,....---.--"""T"""-......-----~----~ 200 l---4--+--..¡._-1--__¡._--J,.._...J-_4-_..IJ

~ § 20

~ t101--.....¡..c¡~.._-+-~~'+__;_+:..:.~~-+

o g ::! 5 ¡:;......,~....;._...+--,;.t-+--+--+---+---+---11

t +I

INERTIAL NAVIGATIO 0.5 ~--..... .;,:,;,;:~-;,¡¡m-.¡.¡,,;,,¡;¡~-·-+----!

o 10 20 30 40 50 60 70 80 90

INCLINATION, DEGREES • After Wolff/deWardt

Figure 3-11 Expected lateral uncertainty in a deviated well considering various types of surveys. (Modified from Wolff and de Wardt 1981. Published by permission of the Journal of Petroleum Technology and Gyrodata, lnc.)

1 2 3

RESISTIVIT Y l_

Figure 3·12 Different hydrocarbon/water contacts caused by directional survey er- :'.' rors.

-<>-~-~

o

----

o 1

SCALE

A-2

~ ...... ' .... , ,, .A-5

' / .................. // ----- ......... // ------ ................ //

500'

SCALE

.,

-8870

500'

...... _ --- '......... // - .... /

/ I

/ I

I I

I I

I /

I

4A-3

(a)

(b)

--- ........ /

- - - - ..._'n~/

/ /

1>-:-"~_:------~A-6 / ...............

I ' I ',

I ' , / ',,

// .............. I ',._

I '' A-4 I •

.A-7

7 A·7

• 7547

Figure 3·13 (a) Straight-lfne method of plotting directional wells in map vlew. (b) Detailed plot of directional survey data indlcating the location and subsea depth of the wellbores along thelr entlre length. Compare thls plot to that In Fig. 3-13a.

33

34 Chap. 3 / Directionally Drilled Wells and Directional Surveys

SLWACE LOCATION MAP VIEW PLOT OF DIRECTIONAL WELL

~o&.-.t-•---J-~ 8 ~ --0-9 --...---Z ---...-- --~- - - 1 BHL

5,000'

6,000'

7 ,000'

8,000'

9,000'

10,000'

11,000'

12,000'

---o---..... -- , 11,494'

CROSS SECTIONAL VIEW OF DIRECTIONALLY

DRILLED WELL

PLOT OF DIRECTIONAL WELL FOR

BASE MAP PREPARATION

Figure 3·14 Cross-sectional view of a directional well and its detai led map view plot in increments of 500 ft.

c.> U1

~-

~_..;---~

~ ':"::' .. -

~~-

.J =--~ -

A

·t· 1

GARDES Dl•lC~AL --.L•• . .C.

.....

\ ..

/ ·'

Figure 3-15 Spider directionat well plot for the Cognac "A" Platform, Offshore Gulf of Mexico. (Published by permission of Gardes Directional Drilling.)

/'-. ,,.

36 Chap. 3 / Directionally Drilled Wells and Directional Surveys

DIRECTIONAL WELL PLOTS

Directional survey data are used to calculate the position and depth of the borehole along its entire length. These data are normally plotted on a base map in one of two ways: (1) as straight lines from the surface to bottom hole location, or (2) as detailed directional plots.

The simplified straight line method of plotting a directional well is shown in Fig. 3-13a. The only data required and plotted on the base map are the surface and bottomhoJe locations. At times, the measured depth to TD is recorded next to the bottomhole location. A straight dashed line is usually drawn between the surface and bottomhole locations. This directional well plot provides absolutely no information about the position or depth of the wellbore in the subsurface between the surface and bottomhole locations. Such a plot is not helpful in the interpretation, construction, and evaluation of fault, structure, or isopach maps.

When directional survey data are actually plotted to provide detail as to the position and subsea depth of the wellbore throughout its en tire length as shown in Fig. 3-13b,· the plot has real value. Such a plot provides a visual guide (in map view) to the location and subsea depth of the wellbore anywhere along its path. It saves time in preparing sub­surface maps and is extremely helpful in the interpretation, construction, and evaluation of fault. structure, and isopach maps. La ter chapters examine several important benefits to fault surface and structure mapping derived from plotting the actual position and subsea depth, at evenly spaced increments (usually 500 ft or 1000 ft) of all directional wells on a base map.

Figure 3-14 illustrates the cross-sectional view of a directionally drilled well and the detailed map view plot of the directional data in 500-ft increments (TVD) along the actual well path. If subsea data are planned for mapping, the directional well data are corrected to subsea before being plotted on the base map.

Figure 3-15 shows the map view well plot for the Cognac ''A'' Platform in the Mississippi Canyon Block 194 in the US Gulf of Mexico. The platform is the largest multiple well platform in the world with 62 slots. The platform is located in 1000 ft of water and has a total height of 1260 ft. Wells were deviated with high angles, up to 75 deg. Horizontal displacement for the wells, up to 11,500 ft, results in a well pattern that covers over a 2-mi radius from the platform, or a diameter of 4.4 mi. Total cost for the project was approximately $960 mil/ion.