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The West Texas (Permian) Basin is a complexly structured intracratonic (IC) basin with prolific oil and natural gas production. It began as a subsidence basin ('Tobosa Basin') from Middle Ordovician to Devonian time, a response to the Cambrian rifting that separated Gondwana and Laurentia. In the Pennsylvanian to early Permian, it formed part of the Ancestral Rocky Mountains (ARM) orogen. The Texas-New Mexico segment of the ARM contains small to medium basement-cored uplifts, folds, thrust faults and two trends of strike-slip faults, with a pattern that is consistent with SW-NE compression. The largest thrust fault known in the basin is SW-vergent, and faces the deepest part of the Delaware Basin. This direction of compression is similar to that observed in the southern Oklahoma part of the ARM, which shows NE-vergent thrusting and left-lateral faulting.

This SW-NE compressive stress is grossly inconsistent with the northwestward convergence of the Ouachita-Marathon thrust belt southeast of the ARM. The ARM-generating stress may have originated either from the Pacific side (by flat subduction) or from strong continental collision in the Appalachian Orogen. Lines of weakness generated during the Proterozoic and/or Cambrian concentrated stress and created the complex structures.

The West Texas branch of the ARM is buried by over 2.5 km of post-deformational Permian strata -- the Permian Basin. Subsidence began during ARM deformation, then increased in rate and continued to the end of the Permian. Permian subsidence resulted in the maintenance of isolated deep-water marine basins until Late Permian time. The Marathon orogen also subsided, and shed little clastic material into the basin. Despite Mesozoic basin-margin modifications, the Permian isopach pattern suggests a bowl-shaped subsidence centered on the Central Basin axis of uplift. The size and shape of the Permian Basin are similar to other IC basins (Illinois, Michigan, Williston). Similar to some IC basins, the central basin area hosts a 1100-Ma mafic complex, which was subjected to compression in Pennsylvanian time. Sinking of a mafic crust or its subjacent lithosphere, begun during compression, may have been a driving force for Permian subsidence.

Over most of the basin, later Permian subsidence was responsible for putting source rocks into the oil window. Further maturation to gas occurred within the deep basins generated by ARM deformation and Marathon thrust loading.

Show more American Association of Petroleum Geologists (AAPG)
Desktop /Portals/0/PackFlashItemImages/WebReady/dl-thomas-ewing-tectonics-and-subsidence-in-the-west-texas-hero.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Tectonics and Subsidence in the West Texas (Permian) Basin, A Model for Complex Intracratonic Basin Development
 

Comparison of the hydrocarbon systems and geometries of the complex intracratonic West Texas (Permian) Basin and the complex postrift subsidence basins of the Gulf Coast / Gulf of Mexico yield useful insights for basin evolution and play development. The West Texas basin contains source rocks in the Ordovician and Devonian, but much generation comes from the Late Mississippian, Pennsylvanian and Permian basinal sediments. These were deposited in a poorly ventilated remnant basin during compression and strike-slip of the Ancestral Rocky Mountains orogeny, and subsidence of the intracratonic Permian Basin. Maturation resulted from Permian intracratonic subsidence, with hydrocarbons sealed from later leakage by late Permian salt and a fortunate tectonic setting. By contrast, the major Jurassic source rocks of the Gulf basins are at the base of the postrift subsidence, and are matured by further subsidence. Later Cretaceous source rocks (Eagle Ford) are mature in the main Gulf basin, but again lie near the bottom of the thick sedimentary package in the area. The younger part of the succession yields mostly gas formed during outbuilding of the shelf margin by Cenozoic deltaic progradation. No cap is present on the basin (except for subsalt plays), and seepage is widespread.

Show more American Association of Petroleum Geologists (AAPG)
Desktop /Portals/0/PackFlashItemImages/WebReady/dl-thomas-ewing-tale-of-two-basins-hero.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true A Tale of Two Basins: Sources and Timing of Petroleum and Natural Gas Generation in the Mature Gulf Coast/Gulf of Mexico and West Texas (Permian) Basins
 

The Yegua Formation (Late Middle Eocene) is a minor siliciclastic progradation of the Gulf of Mexico shelf margin between the larger Early Eocene and Oligocene shelf-margin progradations. During Yegua time (and unlike the other units of the Middle and Late Eocene), four to eight sea-level fluctuations with a 100-300 ka period alternately pushed marine rocks toward the basin margins and pushed deltaic sedimentation to and past the shelf edge. Because of limited to moderate sand supply and the flat coastal plains, the updip (highstand) depositional complexes are nearly entirely separated from the downdip (lowstand) shelf-edge deltas and slope fans. Maximum flooding surfaces can be mapped over much of the area and correlated along and across the basin. The Yegua is truly a laboratory for sequence stratigraphy. A number of plays in the downdip and 'mid-dip' (incised valley complexes) trends have produced over 4 TCF of gas and condensate, and new discoveries await the return of exploration capital. The Yegua story is significant to all those interested in siliciclastic stratigraphy in passive-margin settings.

Show more American Association of Petroleum Geologists (AAPG)
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The Ice Age and the Giant Bakken Oil Accumulation

The USGS estimated (2013) that the Late Devonian to Early Mississippian Bakken Formation holds in excess of 7 billion barrels (~1.1 billion m3) of recoverable oil, making it one of the top 50 largest oilfields in the world. Most of the production comes from shallow-marine sandstones of the Middle Bakken Member that are directly over- and underlain by extremely organic-rich shale source rocks (Upper and Lower Bakken Shale members respectively). Although not oil-productive everywhere, the Middle Bakken forms a relatively sheet-like unit that covers an area of over 200,000 square miles (~520,000 km2) of the intracratonic Williston Basin.

The vertical juxtaposition of shallow-marine reservoir and more distal source rocks over such a large area, without intervening transitional facies, is unusual from a stratigraphic perspective. One possible explanation would require global fluctuations of sea level to drive geologically rapid and extensive shoreline movements in this relatively stable basin. Forced regression associated with falling sea level could explain the lack of transitional facies (e.g., inner shelf) between the distal Lower Bakken Shale and the overlying Middle Bakken (a sharp-based shoreface). Subsequent sea-level rise would have caused rapid and extensive transgression, leading to the observed stratigraphic relationships between the Middle and Upper Bakken members. But what could have caused the changes in sea level?

A considerable body of evidence points to a Late Devonian-Early Mississippian ice age that covered portions of Gondwana (e.g., parts of present-day Brazil) that were situated close to the paleo South Pole. This ice age consisted of more than one glacial/interglacial cycle and was probably triggered by massive removal of CO2 from the atmosphere by land plants and organic-rich shales. Some evidence indicates that at least 100 m of sea-level drop took place during one of the Famennian glaciations, which would have effectively drained the Williston Basin and induced major shoreline progradation. Melting of the ice sheets would have caused transgression and reflooding of the basin and deposition of the Upper Bakken Shale. Other basins around the world record similar evidence for glacioeustacy near the Devonian-Mississippian transition. The glacial/interglacial cycles are expressed differently from basin to basin, reflecting the interplay between fluctuations of global sea level and each basin’s history of subsidence and sediment supply.

Show more American Association of Petroleum Geologists (AAPG)
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Five Things Geophysicists Should Know About Shale Plays

The Shale Revolution caught geophysicists off guard. Shales had been studied for a variety of reasons (e.g., relationships between velocity, compaction and pore pressure) but not as low-porosity reservoirs that show vertical heterogeneity at all possible scales. Consequently, many geophysicists have framed shale-play imaging problems using inappropriate tools and paradigms. In this presentation, I present five characteristics of shale plays that should enable improved geophysical analyses.

  1. The term “shale play” has become meaningless. Originally intended to describe gas production from fine-grained source rocks (“source-rock reservoirs”), the term is now applied almost indiscriminately to production from many types of low-permeability rock (e.g., shaly sandstones, carbonates).
  2. Source-rock reservoirs aren’t clay dominated. Hydraulic fracturing is needed to establish commercial production from these rocks. Clays make the rocks ductile and harder to fracture. As such, the clay content of shale plays is generally less than 50%. The remainder of the rock is usually composed of fine-grained calcite and/or quartz, organic matter and other minerals.
  3. Links between VTI anisotropy and clay or organic content are not straightforward in source-rock reservoirs. Scanning electron microscopy often reveals textures that are incompatible with the conceptual models used to develop mathematical models of shales.
  4. HTI anisotropy is complicated by natural fracture geometries. Aligned natural fractures generally combine with bedding to produce systems that are best described as orthorhombic. In some cases, multiple fracture orientations produce systems that are effectively isotropic.
  5. Integration of geophysical and geological data and concepts is needed to significantly advance geophysical research on shale reservoirs. This effort will allow geophysicists to define, for a specific shale, which assumptions are reasonable, which analogs are appropriate, what appropriate ranges of properties are, etc.
Show more American Association of Petroleum Geologists (AAPG)
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The AAPG Annual Convention and Exhibition will feature a variety of field trips that will bookend the meeting, spanning from March 26 to April 8.

American Association of Petroleum Geologists (AAPG)
Desktop /Portals/0/PackFlashItemImages/WebReady/field-trips-set-for-ace-hero.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Field Trips Set for ACE
 

Last year, the extraordinarily high quality of the technical program was the talk of the AAPG Annual Convention and Exhibition in Calgary, and this was at an ACE with plenty of high points to talk about. The technical program for the 2017 ACE in Houston promises to be even better than last year’s.

American Association of Petroleum Geologists (AAPG)
Desktop /Portals/0/PackFlashItemImages/WebReady/explorer-cover-2017-03mar.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Centennial ACE Boasts Record Abstract Submissions
 

Rock-Eval hydrogen index (HI) is often used to compare relative maturities of a source horizon across a basin. Usually, there are several measurements from the source horizon at a single well, and the mean hydrogen index is calculated, or the S2 is plotted against TOC. The slope of the best fit line through that data is used as the representative HI for that well (sometimes referred to as the ‘slope HI ’ methodology). There is a potential flaw in both these methodologies; however, that renders the calculated HI as misleading if the source horizon being examined is not relatively uniform in source quality, vertically in the stratigraphic column. From a geologic perspective, it would be unusual for the source rock quality not to vary vertically in the stratigraphic column. Organic matter input, preservation, dilution, and sediment accumulation rate typically vary in many depositional environments over the millions of years required to create a thick source rock package. Nevertheless, there are source rocks which do display remarkable source-quality uniformity from top to bottom of the stratigraphic package. We have examined source rocks from several basins where the source quality is relatively uniform over the stratigraphic column, and source rocks where the source quality varies greatly over the stratigraphic column. Methodologies to assess hydrogen index at specific wells for the se two scenarios differ. Most geoscientists may not be familiar with why a single technique is not suitable for both these scenarios, or how to correctly use hydrogen index as a relative maturation proxy in the case where source rock quality is not uniform. We will demonstrate how to determine if your source rock quality is uniform or varied relative to HI over the stratigraphic column, and how to assign a hydrogen index to the different source facies when that source rock quality is not uniform. Further we will illustrate how to estimate the original hydrogen index of the different source facies and assign each a transformation ratio. The transformation ratio is a better proxy for relative maturity, since different source facies may have different present-day hydrogen indices, but their present-day transformation ratio should be quite similar.

Show more American Association of Petroleum Geologists (AAPG)
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The AAPG Annual Convention and Exhibition will feature a variety of field trips that will bookend the meeting, spanning from March 26 to April 8.

American Association of Petroleum Geologists (AAPG)
Desktop /Portals/0/PackFlashItemImages/WebReady/field-trips-set-for-ace-hero.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Field Trips Set for ACE
 
Desktop /Portals/0/PackFlashItemImages/WebReady/dl-gas-hydrate-petroleum-system-analysis-in-marine-and-arctic-permafrost-environments-hero.jpg?width=100&h=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Gas Hydrate Petroleum System Analysis in Marine and Arctic Permafrost Environments
In-Person Training
London Aberdeen City United Kingdom 14 October, 2017 15 October, 2017 40509 Desktop /Portals/0/PackFlashItemImages/WebReady/ice-2017-sc-3-advanced-sequence-stratigraphic-applications-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true SEPM, Sedimentology and Stratigraphy, Sequence Stratigraphy, ICE 2017
 
London, Aberdeen City, United Kingdom
14-15 October 2017

In Conjunction with AAPG/SEG 2017 International Conference & Exhibition (ICE)
A short course to refresh concepts and terminology of sequence stratigraphy and then explore more advanced concepts of Sequence Stratigraphy and its impact on Exploration and Production using hands on exercises and discussions.

Marrakech Morocco 01 November, 2017 04 November, 2017 37903 Desktop /Portals/0/PackFlashItemImages/WebReady/gtw-afr-the-paleozoic-hydrocarbon-potential-of-north-africa-past-lessons-and-future-potential-2017-17apr17-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Engineering, Development and Operations, Production, Infill Drilling, Geochemistry and Basin Modeling, Petroleum Systems, Source Rock, Thermal History, Geophysics, Clastics, Sedimentology and Stratigraphy, Conventional Sandstones, Sequence Stratigraphy, Structure, Compressional Systems, Extensional Systems, Tectonics (General), Deep Basin Gas, Stratigraphic Traps, Structural Traps
 
Marrakech, Morocco
1-4 November 2017

This workshop provides the opportunity to learn and discuss the latest knowledge, techniques & technologies applied to petroleum reservoirs in the Paleozoic of North Africa which can be utilized to explore for and develop these reservoirs. The workshop will provide a set-up for networking, interacting & sharing expertise with fellow petroleum scientists interested in developing and producing hydrocarbon resources within the Paleozoic of North Africa.

Marrakech Morocco 03 November, 2017 04 November, 2017 41272 Desktop /Portals/0/PackFlashItemImages/WebReady/gtw-afr-the-paleozoic-hydrocarbon-potential-of-north-africa-past-lessons-and-future-potential-2017-17apr17-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Structure, Geochemistry and Basin Modeling, Sedimentology and Stratigraphy, Geophysics, Engineering, Compressional Systems, Tectonics (General), Extensional Systems, Source Rock, Petroleum Systems, Thermal History, Sequence Stratigraphy, Clastics, Development and Operations, Production, Structural Traps, Deep Basin Gas, Stratigraphic Traps, Conventional Sandstones, Infill Drilling
 
Marrakech, Morocco
3-4 November 2017

Location: Atlas; Anti-Atlas of Marrakech and Ouarzazate areas of Morocco**
Field Trip Leader: Abdallah Aitsalem (ONHYM) & Lahcen Boutib (ONHYM)
Field Trip Fee: USD575 *

* Field trip pricing covers accommodation, feeding and transportation for the duration of the Trip. Seats are limited and will be confirmed on a first come first served basis.

Day 1 Departure from Marrakech to Ouarzazate

The Atlas Mountains of Marrakech extend more than 250 km East-West and 50 km North-South. They record the highest mountainous peaks in North Africa with altitudes exceeding 4,000 meters (Toubkal 4,165m and Ouenkrim 4,089m). Northward and southward, they rise hundreds of meters above the Marrakech plain (Haouz plain) and Imini syncline, respectively. The recently incised mountain valleys, created during the last inversion of the Atlas, form the crossing ways of the massif, as is the case of the main road that connects Marrakech to Ouarzazate passing via the Tizi n'Tichka Pass. They also provide the opportunity to view multiple breathtaking landscapes and contain outcrops that shed light on the geological evolution of the mountain from the Precambrian to the present. Day 1 of the field trip will allow participants to view Paleozoic outcrops through the Tizi n'Tichka Pass, which displays a complete Cambrian to Devonian succession and contains several organic-rich intervals. Mesozoic and Cenozoic deposits, which are exposed on the borders of the massif, will also be viewed briefly.

Day 2: Departure from Ouarzazate to Tazzarine and back to Ouarzazate **

Day 2 of the field trip crosses the central Anti-Atlas Paleozoic basin and offers spectacular views of the largest oasis in North Africa, along the Draa River, and its majestic ancient Kasbahs. Participants will examine formations ranging in age from Upper Precambrian to Silurian. Discussions will focus on the evolution of their various depositional environments in relation to sea level changes. The well exposed sandstone formations provide the opportunity to view major Paleozoic reservoirsintervals, as well as the organic-rich "hot shales" that source these reservoirs. Rubble from recent water wells and ingenious sub-cropping irrigation systems (Khattara) provide the chance to sample fresh Ordovician and Silurian organic-rich and fossiliferous black shales. In addition, the participants will have perspective views of gentle folding generated during the Hercynian compression and related regional fractures.

Field trip route map
Field trip route map

**Field trip will end in Ouarzazate. All participants to arrange their own transport from Ouarzazate following the conclusion of the field trip.

To register for the field trip please click here.

Online Training
10 May, 2012 10 May, 2012 1486 Desktop /Portals/0/PackFlashItemImages/WebReady/oc-es-genetic-sequences-in-eagle-ford-austin.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true
 
10 May 2012

Recognition and Correlation of the Eagle Ford, Austin Formations in South Texas can be enhanced with High Resolution Biostratigraphy, fossil abundance peaks and Maximum Flooding Surfaces correlated to Upper Cretaceous sequence stratigraphic cycle chart after Gradstein, 2010.

17 February, 2011 17 February, 2011 1469 Desktop /Portals/0/PackFlashItemImages/WebReady/oc-es-siliclastic-sequence-stratigraphy.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true
 
17 February 2011

This presentation is designed for exploration/production geologists and geological managers or reservoir engineers.

14 February, 3000 14 February, 3000 7817 Desktop /Portals/0/PackFlashItemImages/WebReady/oc-es-generic-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true
 
Request a Visit
 

The West Texas (Permian) Basin is a complexly structured intracratonic (IC) basin with prolific oil and natural gas production. It began as a subsidence basin ('Tobosa Basin') from Middle Ordovician to Devonian time, a response to the Cambrian rifting that separated Gondwana and Laurentia. In the Pennsylvanian to early Permian, it formed part of the Ancestral Rocky Mountains (ARM) orogen. The Texas-New Mexico segment of the ARM contains small to medium basement-cored uplifts, folds, thrust faults and two trends of strike-slip faults, with a pattern that is consistent with SW-NE compression. The largest thrust fault known in the basin is SW-vergent, and faces the deepest part of the Delaware Basin. This direction of compression is similar to that observed in the southern Oklahoma part of the ARM, which shows NE-vergent thrusting and left-lateral faulting.

This SW-NE compressive stress is grossly inconsistent with the northwestward convergence of the Ouachita-Marathon thrust belt southeast of the ARM. The ARM-generating stress may have originated either from the Pacific side (by flat subduction) or from strong continental collision in the Appalachian Orogen. Lines of weakness generated during the Proterozoic and/or Cambrian concentrated stress and created the complex structures.

The West Texas branch of the ARM is buried by over 2.5 km of post-deformational Permian strata -- the Permian Basin. Subsidence began during ARM deformation, then increased in rate and continued to the end of the Permian. Permian subsidence resulted in the maintenance of isolated deep-water marine basins until Late Permian time. The Marathon orogen also subsided, and shed little clastic material into the basin. Despite Mesozoic basin-margin modifications, the Permian isopach pattern suggests a bowl-shaped subsidence centered on the Central Basin axis of uplift. The size and shape of the Permian Basin are similar to other IC basins (Illinois, Michigan, Williston). Similar to some IC basins, the central basin area hosts a 1100-Ma mafic complex, which was subjected to compression in Pennsylvanian time. Sinking of a mafic crust or its subjacent lithosphere, begun during compression, may have been a driving force for Permian subsidence.

Over most of the basin, later Permian subsidence was responsible for putting source rocks into the oil window. Further maturation to gas occurred within the deep basins generated by ARM deformation and Marathon thrust loading.

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Request a visit from Thomas Ewing!

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