Facies and Stratigraphy of the San Andres Formation (Mid ...

Facies and Stratigraphy of the San Andres Formation (Mid-Permian) Petroleum Province, Northwest Shelf of the Permian Basin, West Texas: A Resurgent Play

Kevin A. HissDavid B. Williamson

The University of Texas at Dallas

GSA South-Central SectionMarch 9, 2020

• Environments of the San Andres formation on the Northwest Shelf in West Texas

• Complex interaction between sea level, climate, and geomorphology formed “world-class” carbonate reservoirs

• Varying targets for hydrocarbon production

• Quantitative approach to indicate the geologic history of the San Andres and effects of paleoenvironment on reservoir quality

Introduction

upper Leonardian

(Ruppel, 2019)

lower Guadalupian

272.3 Ma

268.8 Ma

Base Roadian

Base Wordian

San Andres Formation Age – Middle Permian

Presenter

Presentation Notes

The middle-Permian San Andres Fm. ranges in age from the uppermost North American Leonardian stage through the lower Guadalupian. Although, precise chronostratigraphic boundaries for the stratotype can’t be constrained.

Yoakum

Roosevelt

Lea

DM

OZONA ARCH

GM

AM

Gaines

AM Apache MountainsDM Delaware MountainsGLM Glass Mountains

OUACHITA OVERTHRUST

Permian BasinNorthwest ShelfStudy AreaAbo Reef Structure

GM Guadalupe MountainsSD Sierra Diablo

NEW

MEX

ICO

TEXA

S

GLM

S. PALO DURO BASIN

SD DELAWARE BASIN

MIDLAND BASIN

EASTERN SHELF

Hockley

Terry

Cochran

(Dutton, 2005; Ruppel, 2019)

San Andres production – shelf and platform carbonate reservoirs

San Andres Reservoirs Occur on Carbonate Platforms and Shelves

Presenter

Presentation Notes

This map shows the locations of San Andres oil & gas production (in blue). The largest reservoirs rim the Midland and Delaware Basins – occurring in shelf and platform carbonates.

Yoakum

Roosevelt

Lea

DM

OZONA ARCH

GM

AM

Gaines


OUACHITA OVERTHRUST



NEW

MEX

ICO

TEXA

S

GLM

S. PALO DURO BASIN

SD DELAWARE BASIN

MIDLAND BASIN

EASTERN SHELF

Hockley

Terry

Cochran

San Andres production – shelf and platform carbonate reservoirs

Cumulative ConventionalPermian Production

San Andres 50%

All other Reservoirs

50%


Trend along the shelf & platform at the margin of Midland Basin

San Andres Reservoirs – Highest Cumulative Production of Permian Basin

Presenter

Presentation Notes

The San Andres has the highest cumulative production of any formation in the Permian Basin. More than 10.7 BBOE have been produced from the San Andres, accounting for ~50% of the conventionally-produced oil in the entire oil province. Notice that there is a clear trend in production on the shelves and platforms along the margin of the Midland Basin. These are “world-class” carbonate reservoirs. San Andres reservoirs on the Northwest Shelf, in particular, are some of the most productive in the Permian Basin. So, what were the geologic and geomorphic controls that formed this uniquely prolific oil province?

Yoakum

Roosevelt

Lea

DM

OZONA ARCH

GM

AM

Gaines


OUACHITA OVERTHRUST



NEW

MEX

ICO

TEXA

S

GLM

S. PALO DURO BASIN

SD DELAWARE BASIN

MIDLAND BASIN

EASTERN SHELF

Hockley

Terry

Cochran

All other Reservoirs(21.2 Bbbl)


Morphology: Broad, low relief (~0.6°)

Dominant lithologies:

Dolomitized carbonates & anhydrites

Depositional environment:

Shallow lagoon & sabkha complexes

Sedimentation pattern:

Upward-shoaling prograding-aggrading sequences

Thickness: 1,200 – 1650 ft.

Rimmed Carbonate Shelf

San Andres Northwest Shelf – Rimmed Carbonate Shelf

Presenter

Presentation Notes

On the Northwest Shelf, the San Andres represents a broad, low relief, rimmed carbonate shelf. The predominant lithologies are dolomitized carbonates and anhydrites that were precipitated in shallow lagoon and sabkha complexes. A hierarchy of sea level fluctuations during an overall middle Permian regression resulted in cyclical stacking of upward-shoaling progradational-to-aggradational carbonate sequences. In the San Andres play fairway of W. Texas, the formation ranges from 1,200 – 1,650 ft. thick.

Yoakum

Roosevelt

Lea

DM

OZONA ARCH

GM

AM

Gaines


OUACHITA OVERTHRUST



TEXA

S

GLM

S. PALO DURO BASIN

SD DELAWARE BASIN

MIDLAND BASIN

EASTERN SHELF

Terry

NEW

MEX

ICO

HockleyCochran

Abo Reef Structure –lower Permian (Leonardian) shelf margin


Carbonate Shelf Rim Overlies a Deep-Seated Shelf Margin

Presenter

Presentation Notes

Oil fields in the San Andres occur where low relief structures overlie deep-seated paleo topographic highs. On these structures, stratigraphically thicker sections of highly porous and permeable carbonates are prominent. The most prominent structural feature trends along the southern margin of the Northwest Shelf (in purple). This structural trend overlies a lower Permian shelf margin, atop the deep-seated lower-Leonardian stage Abo Reef structure.

CumulativeSan Andres Production

All OtherSan Andres Reservoirs(6.7 BBOE)

West TexasSan Andres (4.0 BBOE)

Yoakum

Lea

DM

OZONA ARCH

GM

AM

Gaines


OUACHITA OVERTHRUST



NEW

MEX

ICO

TEXA

S

GLM

SD DELAWARE BASIN

MIDLAND BASIN

EASTERN SHELF

Terry

Roosevelt S. PALO DURO BASIN

HockleyCochran


Abo Reef Structure –lower Permian (Leonardian) shelf marginWest Texas San Andres Play Fairway

San Andres Play Fairway – West Texas

Presenter

Presentation Notes

The most prolific San Andres oil fields are situated in W. Texas, spanning Yoakum, Cochran, W. Hockley, and N.W. Terry Counties (in yellow). Cumulative production from this region is ~4.0 BBOE – nearly 40% of the cumulative total produced from the San Andres in the entire Permian Basin.

Yoakum

Roosevelt

Lea

DM

OZONA ARCH

GM

AM

Gaines


OUACHITA OVERTHRUST



NEW

MEX

ICO

TEXA

S

GLM

S. PALO DURO BASIN

SD DELAWARE BASIN

MIDLAND BASIN

EASTERN SHELF

Cochran Hockley

Terry

(Ramondetta, 1982a; Ramondetta, 1982b; Ruppel, 2019)

SourceRocks

Oil Fields

Migration

Abo Reef

Trend

Abo Reef

Trend

San Andres Play Fairway – West Texas

Presenter

Presentation Notes

In this region, the San Andres play fairway extends southward to the Abo Reef trend. Vertical migration of hydrocarbons through underlying strata – from source rocks of the northern Midland Basin facilitated accumulation in legacy fields along this trend. Traps along the Abo trend filled-to-spill, and lateral migration continued updip (northward), where successive trapping occurred in updip porosity-pinchouts. Reservoir facies grade shelfward into sabkha evaporites and terrigenous continental deposits and terminate along the Matador Uplift (in blue), at the southern margin of the Palo Duro Basin.

Permian Basin

Guadalupian

Equator

(Blakey, 2019)

Warming Climate and Near-Equatorial Latitude: Favorable for Sabkha Evaporites

Presenter

Presentation Notes

Waning-stage glaciation during the early and middle Permian and the shift from an icehouse to a greenhouse climate, coupled with the near-equatorial latitude of the Guadalupian stage Permian Basin, facilitated an increasingly arid climate. At the landward margins of the basin’s shelves and platforms, conditions were favorable for precipitation of sabkha evaporites and thick carbonate successions.

massive & nodular anhydrite

lime-rich mudstone

oolitic packstone and grainstone

algal-coated grainstone & mudstone

supratidalintertidal

subtidalrestricted

shoal activeshoal

N

mudstone & pellet packstone

(Ramondetta, 1982a; Ward et al., 1986)

Inner-Shelf Environments and Facies Tract

Presenter

Presentation Notes

This model shows a typical San Andres shelf facies tract. Supratidal environments were dominantly sabkha anhydrites. The intertidal zones are tidal flat environments - these are mainly mudstones and packstones. Subtidal environments range from a broad, shallow, subtidal lagoon – with lime-rich mudstones in the deeper lagoonal facies, and oolitic packstones and grainstones in the shallower shoal zone.

N

dolomitizing waters

hypersaline waters:supersaturated with dolomite

high porosity dolomite

(Saller, 2004; Ramondetta, 1982a; Ramondetta, 1982b)

Secondary Porosity Formed by Reflux Dolomitization

Presenter

Presentation Notes

Shelf rims facilitated the restriction of inner-shelf environments during sea level lows, creating hypersaline and schizohaline conditions, which were favorable for reflux dolomitization and formation of secondary porosity in inner-shelf carbonates (in blue). During sea level lows, subaerially exposed low-relief structures at the shelf rim were prone to enhanced porosity development due to refluxing of brines during base sea level fluctuations. These high-porosity structures (in yellow) are the primary target for conventional development in the San Andres.

N

dolomitizing waters

hypersaline waters:supersaturated with dolomite

Variable anhydriteplugged dolomite


Porosity Occlusion by Anhydrite Cement

Presenter

Presentation Notes

Dissolution of carbonates in supersaturated brines can also facilitate precipitation of anhydrite cement in the porous dolomitized carbonates. Because dolomitization and anhydrite plugging occur in similar conditions – at sea level lows – the occurrence of pore occlusion can be highly variable over short distances - complicating the distribution of porous reservoir facies in “off structure” targets.

Rise

(Lopez-Gamundi, 2019; Ross and Ross, 1987; Ruppel, 2019)

middle-Permian eustatic regression

San Andreseustatic

transgressions

Hierarchy of Sea Level Fluctuations

Presenter

Presentation Notes

An overall middle Permian sea level regression was punctuated by short-term transgressive pulses during San Andres time.

Rise

𝝅𝝅 Marker

UpperSan Andres

LowerSan Andres

UpperSan

Andres

LowerSan

Andres

(Lopez-Gamundi, 2019; Ross and Ross, 1987; Ruppel, 2019)

𝝅𝝅 Marker Bed Deposited at Sea Level Lowstand

Presenter

Presentation Notes

A regionally ubiquitious time-stratigraphic supratidal marker bed, known regionally as the Pi marker, was deposited across the San Andres shelf during the sea level lowstand – this marks the boundary between the Lower and Upper San Andres.

T

T

T

T

T

T

T

T

T

T

TR

R

R

R

R

R

R

R

R

R

R

Rise

High-FrequencyT-R Cycles

𝝅𝝅 Marker

UpperSan Andres

LowerSan Andres

UpperSan

Andres

LowerSan

Andres(Lopez-Gamundi, 2019; Ross and Ross, 1987; Ruppel, 2019)

High-Frequency Transgressive-Regressive Cycles

Presenter

Presentation Notes

Contributing further to the hierarchy of sea level fluctuations during San Andres time, higher-frequency transgressive-regressive cycles are well-defined by facies offset in the San Andres, and facilitate cyclical stacking of porous subtidal, and tight supratidal facies.

Tight Supratidal Anhydrites & High Porosity Subtidal DolomitesN– Porosity +

basinward


Presenter

Presentation Notes

Subtidal shoals were more prone to porosity enhancement by reflux dolomitization. Lagoonal and intertidal facies are increasingly tight and commonly have a highly variable porosity distribution – due to anhydrite-plugging of porous dolomite facies in dolomite-saturated hypersaline waters. Supratidal sabkha evaporites (anhydrites) are impermeable. Anhydrites and anhydritic dolomites in the Upper San Andres form an impenetrable seal, which helped to make Lower San Andres carbonates “world-class” reservoirs.

Sea Level

H

L

High-FrequencyT-R Cycles

N

upward-shoaling progradational-aggradational

(Ramondetta, 1982a; Ramondetta, 1982b; Ward et al., 1986)

Cyclical Stacking of Porous & Tight Facies

Presenter

Presentation Notes

This model shows how the hierarchy of sea level fluctuations affected San Andres stratigraphic architecture. High frequency transgressive-regressive cycles facilitated the cyclical stacking of porous and tight lithofacies. As you can see, topographically high shoals become deep-seated structures – influencing the placement and morphology of overlying structures. An overall sea level regression during the middle-Permian, coupled with intermediate transgressive-regressive cycles throughout the Guadalupian, caused an overall upward-shoaling, progradational-to-aggradational, migration of shelf facies.

thick porous dolomite

interbedded dolomite & anhydrite

N

(Ramondetta, 1982a; Ramondetta, 1982b)

Thick Reservoir Facies Grade Northward to Thin Beds

Presenter

Presentation Notes

The relationship between land and subsea facies greatly affected the distribution of San Andres reservoirs. The thickest porous zones, in the southernmost section of the play fairway, grade northward into interbedded anhydrites and dolomites. At the basinward section of the play fairway, subtidal environments were dominant, these fields in have thick, high-porosity pay zones – formed atop deep-seated paleo structures, such as the Abo Reef.

Intercrystalline Macroporosity – Vugular Pores Increase With Depth

(SEM images courtesy of Monadnock Resources, LLC)

intercrystalline macroporosity

Oversized grain-moldic pores

Presenter

Presentation Notes

These photomicrographs, courtesy of Monadnock Resources, are from vertical pilot wells in the San Andres. The red arrows show the typical intercrystalline pore structure in San Andres reservoirs.

Intercrystalline Macroporosity – Vugular Pores Increase With Depth

intercrystalline macroporosity

(SEM images courtesy of Monadnock Resources, LLC)

Oversized grain-moldic pores

vugularporosity increases with depth

Presenter

Presentation Notes

The green arrows show oversized voids. These grain-moldic pores increase with depth, and are, therefore, more common in the thicker reservoir sections, especially along the southern margin of the play fairway.

Thick Reservoir Facies Grade Northward to Discrete Beds

thick porous dolomite

interbedded dolomite & anhydrite

N


Presenter

Presentation Notes

In the northernmost section of the play fairway, cyclical stacking of intertidal and supratidal facies created thinner, discrete, porous pay zones, separated by anhydrite seals and anhydritic dolostones.

Compaction Drape and Fracturing Atop Low-Relief Structures

propagation of fracturesunder the overburden

carbonate shoal: Cycle 2



compaction

fractures in limestonebetween shales

fractures on crest

lagoonal mudstones

Ramp

lagoonal mudstones

North South


Further Burial and Compaction

Shallow Burial and Compaction of Mudstones

Deposition of CarbonatesI

II

III

Abo Reef

Trend

Presenter

Presentation Notes

Successive deposition and burial of carbonates and mudstones atop, and on the margins of, the low relief shelf rim – also known as the Abo Trend – facilitated vertical fracturing along the crest of these structures. Continued burial and compaction facilitated the deepening of fractures. Dolomitizing waters were able to permeate through these fractures – further enhancing porosity and creating a migration pathway for hydrocarbon expulsion into the reservoir.

Outcrops in Guadalupe Mts. - ~150 mi. From W. Texas Reservoirs

WassonLevelland Brahaney

1 2 34

1 2 3 4Slaughter

Rio Hondo Rio Penasco Algerita Escarpment

NEW

MEX

ICO

TEXA

S

Guadalupe

Mts.

Northwest Shelf, W. Texas

(Kerans, 2014; Ruppel, 2019)

Presenter

Presentation Notes

Dr. Charles Kerans modeled San Andres stratigraphy from outcrop in the Guadalupe Mountains, north of the Delaware Basin (~150 miles from the study area) and used that model to describe the stratigraphic position of oil fields north of the Midland Basin.

Progradational-Aggradational San Andres Shelf Migration

NEW

MEX

ICO

TEXA

S

Guadalupe

Mts.


Guadalupe Mts.N S

(Kerans, 2014; Ruppel, 2019)

Presenter

Presentation Notes

Notice the prograding-aggrading nature of shelf environments in response to sea-level changes as the Permian carbonate margin stepped basinward. The best reservoir facies were deposited along the restricted shelf (in orange).

Oil Fields Occur in Increasingly Younger Strata – Offsetting Basinward

WassonLevelland Brahaney

1 2 34

1 2 3 4Slaughter

1

2

3

4


Guadalupe Mts.

youngest oldest

N S

(Kerans, 2014)

Presenter

Presentation Notes

Oil fields in this region, according to Kerans’ model, occur in increasingly younger strata – offsetting basinward.

Sabkha Evaporites Extend Southward During Mid-Permian Regression

Early Guadalupian (268 Ma)

Late Guadalupian (263 Ma)

San Andres at margin of Midland Basin open marine waters

Continued sea level fall: supratidal sabkhas extend over the Midland Basin

(Blakey, 2019)

Presenter

Presentation Notes

During San Andres time, this region extended along the northern margin of the open marine waters of the Midland Basin. As the middle-Permian eustatic regression continued, supratidal sabkha evaporites continued to extend basinward, sealing Permian Basin reservoirs. In the San Andres, however, the reservoir seal occurs at the Pi Marker – the boundary between the Upper and Lower San Andres.

Structure Map of the 𝝅𝝅 Marker – The Base of the Reservoir SealA

A’


Presenter

Presentation Notes

The contours show shelf structure at the time-stratigraphic Pi Marker. All San Andres reservoirs occur below this stratigraphic level. Above the Pi Marker, anhydrites and anhydritic dolomites of the Upper San Andres provide the seal for the reservoir. As you would expect, the shelf position of structural highs (circled in red) correspond with legacy oil fields.

Inner-to-Outer Shelf Reservoir Architecture

A0

500

1500

1000

2000

2500

Upper San Andres seal

A’sea level

A

A’

AboTrend

Matador Uplift

(Ebanks, 1990; Ramondetta, 1982a; Ramondetta, 1982b)

Presenter

Presentation Notes

The simplified cross section (left) shows the San Andres reservoir architecture – from north to south. The shelf dips gently (~0.5°) toward the basin. Because of the continuous forward-and-backstepping of shelf environments, successive stratigraphic traps were established in the form of updip porosity pinchouts. The red arrows correlate with structural highs circled along the cross-section line (right).

A0

500

1500

1000

2000

2500

Upper San Andres seal

A’sea level

A

A’

AboTrend

Matador Uplift spill

pointspill

pointspill

point

(Ebanks, 1990; Ramondetta, 1982a; Ramondetta, 1982b)

Migration and Successive Trapping in Updip Porosity Pinchouts

Presenter

Presentation Notes

Hydrocarbons migrated vertically, through the Abo Trend – at the southern margin of the play fairway. Once they encountered the Upper San Andres seal, they continued updip, and filled-to-spill the structurally low-relief reservoirs. Migration and filling of the Lower San Andres reservoirs is thought to have continued – forming a, once, much larger paleo oil reservoir.

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Vertical Oil Saturation Profile

(Ruppel, 2019; Trentham and Melzer, 2019)

main pay zone: vertical target – occurs on low-relief structures

transitional oil zone:water-laden interval (decreasing oil saturation with depth & increasing water saturation)

Goldsmith Landreth San Andres Unit, Ector Co., TX

Oil Saturation (%)

Oil-water contact

Oil Saturation Continues Below the Conventional Fields

Presenter

Presentation Notes

The diagram shows the oil saturation profile in the San Andres Fm. for a well in Ector Co., TX. The main pay zone is the target for vertical development in legacy fields. As you would expect, this interval has the highest oil saturation. However, saturation continues below the oil-water contact – into the transitional oil zone.

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Oil Saturation (%)

Oil-water contact

(+) water saturation

(-) oil saturation


Oil Saturation Decreases With Depth; Water Saturation Increases

Presenter

Presentation Notes

Below the oil-water contact - as depth increases, water saturation increases, with a proportionate decrease in oil saturation.

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Oil Saturation (%)

San Andres basal limestone:Minor oil saturation indicates previous saturation to the base of the reservoir

Oil-water contact

(+) water saturation

(-) oil saturation


Indication of a Larger Paleo Oil Trap and Subsequent Flushing

Presenter

Presentation Notes

Interestingly, there is minor oil saturation in the basal limestone – indicating that this reservoir was once saturated all the way down to the base of the porous dolomite facies. So, what happened?

A A’

A A’

(Melzer, 2006; Ruppel, 2019)

Uplift and Exposure of Guadalupian Strata in New Mexico

Presenter

Presentation Notes

Uplift in New Mexico - associated with Laramide Orogeny tectonism – exposed Guadalupian strata. Creating an avenue for an influx of meteoric water into the San Andres reservoir.

(Ruppel, 2019; Trentham et al., 2015)

Influx of Meteoric Water and Sweeping of the Lower Oil Column

Presenter

Presentation Notes

On the left is a map of “fairways of sweep” throughout the San Andres reservoirs in the Permian Basin. The proposed pathways for water migration are shown in blue and San Andres oil fields are in shown green.

(Trentham et al., 2015)

Flushing of the Lower Oil Column

Presenter

Presentation Notes

In this region, the lower oil column was flushed in the southeast direction – following the dip of San Andres shelf.

(Melzer, 2006)

main pay zone (MPZ)

vertical target – on structural highs

transitional oil zone (TZ)

150-300 ft. thick water-laden interval below oil-water contact

residual oil zone (ROZ)

no primary oil recovery

horizontal target

Resurgent Play Extends Beyond the Flanks of Legacy Fields

Presenter

Presentation Notes

Legacy oil fields have a main pay zone. In other words – an economic conventional target for production via vertical wells. Beyond the flanks of legacy fields, the transitional oil zone - a 150-300 ft. thick interval that contains primary oil – or oil that is mobile and can be produced without secondary or tertiary recovery methods – is the target for the resurgent San Andres play. Although the transition zone has lower oil saturations, it’s still an economic target for horizontal drilling operations. Below the transitional zone, the residual oil zone has no mobile oil and is not a target for primary recovery.

Petrophysical Analysis Indicates Prograding-Aggrading Shelf

Presenter

Presentation Notes

Contrary to the typical approach of studying sedimentary facies and stratigraphy to identify drilling targets, this study utilized whole-core and petrophysical data from San Andres wells to confirm the progradational-aggradational nature of San Andres shelf strata. The map (left) shows a 431 sq. mi. area within Yoakum Co. Detailed petrophysical analyses were conducted for 73 wells (in blue). Dark red lines note the limits of vertical production (i.e., all wells outside of these fields are penetrating “off structure” strata).

N Methodology:

1. Calculate oil-in-place from petrophysical analyses

2. Indicate the depth of most saturated 100 ft. reservoir interval

3. Contour similar depths


Presenter

Presentation Notes

For each well, total oil in place was calculated from petrophysical analyses. The interval with the best 100 ft. of reservoir (i.e., the interval with the highest calculated oil in place) was plotted. The depth of the interval with the “best 100 ft.” is indicated by the contours. The sub sea-level depth is represented by the scaled color scheme.

NResults:

The depth of the “best 100 ft.” interval indicates the depth of the restricted shelf margin.

Moving basinward (southeast), the depth of the restricted shelf margin indicates progradational-aggradational shelf migration.


Presenter

Presentation Notes

Keeping in mind that the best reservoirs occur on the basinward margins of the restricted shelf, it’s clear that the data confirms the progradational-aggradational migration of shelf facies.

NResults:

The depth of the “best 100 ft.” interval indicates the depth of the restricted shelf margin.

Moving basinward (southeast), the depth of the restricted shelf margin indicates progradational-aggradational shelf migration.


Presenter

Presentation Notes

Moving from shelf-to-basin (northwest-to-southeast), the progradational and aggradational migration of the shelf margin is clear. Where the contours are more widely distributed, it’s an indication of shelf environments stepping toward the basin. Where they’re closer together, it’s an indicator of a more aggradational movement.

N

Core Properties Within the “Best 100 Ft.” of Reservoir

Presenter

Presentation Notes

The grid on the right is of the same area. This map shows the distribution of wells with “whole core” data. Shown in blue are 25 “on structure” wells (i.e., wells within vertical fields). From these wells, 1,285 data points fall within the “best 100 ft.” of reservoir. 41 wells penetrating “off structure” targets (i.e., targets of the resurgent San Andres play) beyond the flanks of vertical fields contained data within the “best 100 ft.” interval. This study includes a comparative analysis of reservoir properties within the “best 100 ft.” interval in both targets.

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Por

osity

[%]

Percent Greater Than

In Out

Porosity of “In Field” & “Off Structure” Core Points

Core Properties Indicate Porosity Enhancement on Paleo-Structural Highs

Presenter

Presentation Notes

The “probability of exceedance” curve (left) indicates the “degree of certainty” for porosity values at any given point within the best 100 ft. of reservoir. The blue line represents porosity values for “in field” reservoir, and the orange line represents “off structure” reservoir.

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osity

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Presenter

Presentation Notes

For example, the curve shows that, of our 1,285 “in field” core points, there was a 90% certainty that the porosity value of any particular point would be higher than 3.3%. Likewise, there was 10% certainty that the porosity would be greater than 13.3%.

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Por

osity

[%]


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porosity enhancement of “in field” reservoir facies


Presenter

Presentation Notes

More importantly, the data clearly indicates that “in field” reservoir facies have enhanced porosity relative to “off structure” targets.

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mea

bilit

y [m

D]


In Out

Core Properties Indicate Permeability Enhancement on Paleo-Structural Highs

Permeability of “In Field” & “Off Structure” Core Points

permeability enhancement of “in field” reservoir facies

Presenter

Presentation Notes

Likewise, the data for permeability shows the same trend – with “in field” reservoir facies showing enhanced permeability relative to “off structure” targets.

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er S

atur

atio

n [%

]


In Out

Water Saturation of “In Field” & “Off Structure” Core Points

greater water saturation in “off” structure reservoir

Core Properties Indicate Greater Water Saturation in “Off” Structure Reservoir

Presenter

Presentation Notes

Core analyses also indicate higher water saturation in “off structure” strata.

Water SaturationPermeabilityPorosity

• porosity enhancement by secondary dolomitization

• porosity occlusion in lagoonal or intertidal facies

• paleo-waterflood and sweeping of the lower oil column

Reservoir Quality Diminishes Off the Flanks of Legacy Fields

Presenter

Presentation Notes

From this data, it’s clear that reservoir quality diminishes off the flanks of legacy fields. For producers, this is an indicator of why it’s necessary to pursue the resurgent San Andres target with unconventional drilling methods. From a purely geological standpoint, this is a more quantitative depiction of the effects of porosity enhancement by secondary dolomitization on structural highs. Or porosity occlusion in lagoonal or intertidal facies – due to precipitation of anhydrite cement in hypersaline environments. The contrasts in water saturation are also a clear indication of which intervals of the reservoir were more thoroughly flushed during the paleo-waterflood.

• The San Andres Fm. on the Northwest Shelf in W. Texas represents a “world-class” carbonate hydrocarbon reservoir – formed by the complex interactions of supratidal and subtidal environments during a hierarchy of sea-level fluctuations and increasingly arid climatic conditions

• A paleo-waterflood flushed the lower oil column of the reservoir, leaving a distribution of distinct targets for production that vary in oil-water saturation, distribution, and method of production

• Petrophysical and core analyses of these targets provide a quantitative method of analysis of the prograding-aggrading migration of shelf environments, and the diminishing reservoir quality, moving from the “in field” to “off” structure reservoir

Takeaways

Blakey, R., n.d., Greater Permian Basin: http://deeptimemaps.com/greater-permian-basin-map-list/ (accessed October 21, 2019).

Dutton, S.P., Kim, E.M., Broadhead, R.F., Raatz, W.D., Breton, C.L., Ruppel, S.C., and Kerans, C., 2005, Play analysis and leading-edge oil-reservoir development methods in the Permian Basin: Increased recovery through advanced technologies: AAPG Bulletin, v. 89, p. 553–576, doi: 10.1306/12070404093.

Ebanks, W. J., 1990, Geology of the San Andres Reservoir, Mallet Lease, Slaughter Field, Hockley County, Texas: Implications for Reservoir Engineering Projects: Geologic and Engineering Approaches in Evaluation of San Andres/Grayburg Hydrocarbon Reservoirs - Permian Basin, Bureau of Economic Geology, p. 75–85.

Kerans, C., 2014, San Andres Formation: Outcrop to Subsurface Stratigraphic Framework: SlideServe, https://www.slideserve.com/tekla/san-andres-formation-outcrop-to-subsurface-stratigraphic-framework (accessed March 2020).

Lopez-Gamundi, C., 2019, INTEGRATED GEOCHEMISTRY AND SEDIMENTOLOGY OF THE WOLFCAMP B3 AND B2 INTERVALS, MIDLAND BASIN, TX: University of Oklahoma: <https://www.researchgate.net/publication/333516360_INTEGRATED_GEOCHEMISTRY_AND_SEDIMENTOLOGY_OF_THE_WOLFCAMP_B3_AND_B2_INTERVALS_MIDLAND_BASIN_TX> (accessed October 21, 2019).

Melzer, S. L., 2006, Stranded Oil in the Residual Oil Zone: Advanced Resources International and U.S. Department of Energy: Office of Fossil Energy – Office of Oil and Natural Gas: http://residualoilzones.com/wp-content/uploads/2018/02/Melzer2006.pdf (accessed November 17, 2019).

References

Ramondetta, P.J., 1982a, Facies and Stratigraphy of the San Andres Formation, Northern and Northwestern Shelves of the Midland Basin, Texas and New Mexico: Bureau of Economic Geology, The University of Texas at Austin, doi: 10.23867/ri0128d.

Ramondetta, P.J., 1982b, Genesis and Emplacement of Oil in the San Andres Formation, Northern Shelf of the Midland Basin, Texas: Bureau of Economic Geology, The University of Texas at Austin, doi: 10.23867/ri0116d.

Ross, C.A., and Ross, J.R.P., 1987, Late Paleozoic Sea Levels and Depositional Sequences: Cushman Foundation for Foraminiferal Research, Special Publication No. 24.

Ruppel, S.C., 2019, Anatomy of a Paleozoic basin: the Permian Basin, USA: Austin, TX, The University of Texas at Austin, Bureau of Economic Geology, v. 1.

Saller, A.H., 2004, Palaeozoic dolomite reservoirs in the Permian Basin, SW USA: stratigraphic distribution, porosity, permeability and production: Geological Society, London, Special Publications, v. 235, p. 309–323, doi: 10.1144/gsl.sp.2004.235.01.13.

Trentham, B. L., and Melzer, S. L., 2019, A "Cookbook" Approach to Evaluating Residual Oil Zones Completed as Horizontal Depressurizing (DUROZ) Wells in the San Andres Formation: AAPG: Search and Discovery, no. 51570, doi:10.1306/51570Trentham2019.

Trentham, B.L., Melzer, S.L., Vance, D.B., Kuuskraa, V., and Petrusak, R., 2015, Identifying and Developing Technology for Enabling Small Producers to Pursue the Residual Oil Zone (ROZ) Fairways of the Permian Basin, San Andres: Residual Oil Zones, http://residualoilzones.com/rpsea-ii/.

Ward, R.F., Kendall, C. G. ST., and Harris, P.M., 1986, Upper Permian (Guadalupian) Facies and Their Association with Hydrocarbons--Permian Basin, West Texas and New Mexico: AAPG Bulletin, v. 70, p. 239–262, doi: 10.1306/9488566f-1704-11d7-8645000102c1865d.

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