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2615
 
Explorer Geophysical Corner

Last month in this space we analyzed the relations of fracture patterns and layer curvature in clay models. This month we examine these relations in a central Oklahoma field developed by Pathfinder Exploration, Norman, Okla.

2605
 
Explorer Emphasis Article

After decades spent visiting Morocco and neighboring Algeria, an AAPG member who's led countless field trips to some of the earth's most exotic places says the two old countries are evolving into modern times.

5682
 

Prolific hydrocarbon discoveries in the subsalt, commonly known as the “presalt,” section of Brazil and the conjugate African margin have created a business imperative to predict reservoir quality in lacustrine carbonates. Geothermal convection is a style of groundwater flow known to occur in rift settings, which is capable of diagenetic modification of reservoir quality. We simulated variable density groundwater flow coupled with chemical reactions to evaluate the potential for diagenesis driven by convection in subsalt carbonates.

Rates of calcite diagenesis are critically controlled by temperature gradient and fluid flux following the principles of retrograde solubility. Simulations predict that convection could operate in rift carbonates prior to salt deposition, but with rates of dissolution in the reservoir interval only on the order of 0.01 vol. %/m.y., which is too low to significantly modify reservoir quality. The exception is around permeable fault zones and/or unconformities where flow is focused and dissolution rates are amplified to 1 to 10 vol. %/m.y. and could locally modify reservoir quality. After salt deposition, simulations also predict convection with a critical function for salt rugosity. The greatest potential for dissolution at rates of 0.1 to 1 vol. %/m.y. occurs where salt welds, overlying permeable carbonates thin to 500 m (1640 ft) or less. With tens of million years residence times feasible, convection under these conditions could locally result in reservoir sweet spots with porosity modification of 1% to 10% and potentially an order of magnitude or more in reservoir permeability. Integrating quantitative model–derived predictive diagenetic concepts with traditional subsurface data sets refines exploration to production scale risking of carbonate reservoir presence and quality.

3772
 
Understanding the distribution and geometry of reservoir geobodies is crucial for net-to-gross estimates and to model subsurface flow. This article focuses on the process of dolomitization and resulting geometry of diagenetic geobodies in an outcrop of Jurassic host rocks from northern Oman. Field and petrographic data show that a first phase of stratabound dolomite is crosscut by a second phase of fault-related dolomite. The stratabound dolomite geobodies are laterally continuous for at least several hundreds of meters (sim1000 ft) and probably regionally and are one-half meter (1.6 ft) thick. Based on petrography and geochemistry, a process of seepage reflux of mesosaline or hypersaline fluids during the early stages of burial diagenesis is proposed for the formation of the stratabound dolomite. In contrast, the fault-related dolomite geobodies are trending along a fault that can be followed for at least 100 m (328 ft) and vary in width from a few tens of centimeters to as much as 10 m (sim1–33 ft). Petrography, geochemistry, and high homogenization temperature of fluid inclusions all point to the formation of the dolomite along a normal fault under deep burial conditions during the Middle to Late Cretaceous. The high 87Sr/86Sr ratio in the dolomite and the high salinity measured in fluid inclusions indicate that the dolomitizing fluids are deep basinal brines that interacted with crystalline basement. The dolomitization styles have an impact on the dimension, texture, and geochemistry of the different dolomite geobodies, and a modified classification scheme (compared to the one from Jung and Aigner, 2012) is proposed to incorporate diagenetic geobodies in future reservoir modeling.
3770
 

West Edmond field, located in central Oklahoma, is one of the largest oil accumulations in the Silurian–Devonian Hunton Group in this part of the Anadarko Basin. Production from all stratigraphic units in the field exceeds 170 million barrels of oil (MMBO) and 400 billion cubic feet of gas (BCFG), of which approximately 60 MMBO and 100 BCFG have been produced from the Hunton Group. Oil and gas are stratigraphically trapped to the east against the Nemaha uplift, to the north by a regional wedge-out of Hunton strata, and by intraformational diagenetic traps. Hunton Group reservoirs are the Bois d'Arc and Frisco Limestones, with lesser production from the Chimneyhill subgroup, Haragan Shale, and Henryhouse Formation.

Hunton Group cores from three wells that were examined petrographically indicate that complex diagenetic relations influence permeability and reservoir quality. Greatest porosity and permeability are associated with secondary dissolution in packstones and grainstones, forming hydrocarbon reservoirs. The overlying Devonian–Mississippian Woodford Shale is the major petroleum source rock for the Hunton Group in the field, based on one-dimensional and four-dimensional petroleum system models that were calibrated to well temperature and Woodford Shale vitrinite reflectance data. The source rock is marginally mature to mature for oil generation in the area of the West Edmond field, and migration of Woodford oil and gas from deeper parts of the basin also contributed to hydrocarbon accumulation.

3771
 

The Upper Jurassic Arab Formation in the Arabian Peninsula, the most prolific oil-bearing interval of the world, is a succession of interbedded thick carbonates and evaporites that are defined stratigraphically upsection as the Arab-D, Arab-C, Arab-B, and Arab-A. The Arab-D reservoir is the main reservoir in Khurais field, one of the largest onshore oil fields of the Kingdom of Saudi Arabia.

In Khurais field, the Arab-D reservoir is composed of the overlying evaporitic Arab-D Member of the Arab Formation and the underlying upper part of the Jubaila Formation. It contains 11 lithofacies, listed from deepest to shallowest: (1) hardground-capped skeletal wackestone and lime mudstone; (2) intraclast floatstone and rudstone; (3) pelletal wackestone and packstone; (4) stromatoporoid wackestone, packstone, and floatstone; (5) Cladocoropsis wackestone, packstone, and floatstone; (6) Clypeina and Thaumatoporella wackestone and packstone; (7) peloidal packstone and grainstone; (8) ooid grainstone; (9) crypt-microbial laminites; (10) evaporites; and (11) stratigraphically reoccurring dolomite.

The Arab-D reservoir lithofacies succession represents shallowing-upward deposition, which, from deepest to shallowest, reflects the following depositional environments: offshore submarine turbidity fans (lithofacies 1 and 2); lower shoreface settings (lithofacies 3); stromatoporoid reef (lithofacies 4); lagoon (lithofacies 5 and 6); shallow subtidal settings (lithofacies 7 and 8); peritidal settings (lithofacies 9); and sabkhas and salinas (lithofacies 10). The depositional succession of the reservoir represents a prograding, shallow-marine, reef-rimmed carbonate shelf that was subjected to common storm abrasion, which triggered turbidites.

3767
 
Isolated carbonate buildups (ICBs) are commonly attractive exploration targets. However, identifying ICBs based only on seismic data can be difficult for a variety of reasons. These include poor-quality two-dimensional data and a basic similarity between ICBs and other features such as volcanoes, erosional remnants, and tilted fault blocks. To address these difficulties and develop reliable methods to identify ICBs, 234 seismic images were analyzed. The images included proven ICBs and other features, such as folds, volcanoes, and basement highs, which may appear similar to ICBs when imaged in seismic data. From this analysis, 18 identification criteria were derived to distinguish ICBs from non-ICB features. These criteria can be grouped into four categories: regional constraints, analysis of basic seismic geometries, analysis of geophysical details, and finer-scale seismic geometries. Systematically assessing the criteria is useful because it requires critical evaluation of the evidence present in the available data, working from the large-scale regional geology to the fine details of seismic response. It is also useful to summarize the criteria as a numerical score to facilitate comparison between different examples and different classes of ICBs and non-ICBs. Our analysis of scores of different classes of features suggests that the criteria do have some discriminatory power, but significant challenges remain.
3766
 
Jurassic deposition in the Maghrebian tethys was governed by eustasy and rifting. Two periods were delineated: (1) a carbonate shelf (Rhaetian–early Pliensbachian) and (2) a platform-basin complex (early Pliensbachian–Callovian). The carbonate shelf evolved in four stages, generating three sedimentary sequences, J1 to J3, separated by boundary sea level falls, drawdown, exposure, and local erosion. Sediment facies bear evidence of sea level rises and falls. Lateral changes in lithofacies indicate shoaling and deepening upward during the Sinemurian. A major pulse of rifting with an abrupt transition from carbonate shelf to pelagic basin environments of deposition marks the upper boundary of the lower Pliensbachian carbonate shelf deposits. This rifting episode with brittle fractures broke up the Rhaetian–early Pliensbachian carbonate shelf and has created a network of grabens, half grabens, horsts, and stacked ramps. Following this episode, a relative sea level rise led to pelagic sedimentation in the rift basins with local anoxic environments that also received debris shed from uplifted ramp crests. Another major episode spanning the whole early Pliensbachian–Bajocian is suggested by early brecciation, mass flows, slumps, olistolites, erosion, pinch-outs, and sedimentary prisms. A later increase in the rates of drifting marked a progress toward rift cessation during the Late Jurassic. These Jurassic carbonates with detrital deposits and black shales as the source rocks in northeastern Tunisia may define interesting petroleum plays (pinch-out flanking ramps, onlaps, and structurally upraised blocks sealed inside grabens). Source rock maturation and hydrocarbon migration began early in the Cretaceous and reached a maximum during the late Tortonian–Pliocene Atlassic orogeny.
2496
 
Explorer Emphasis Article

Complex considerations: Mention the Bakken Formation and most people think of unlimited potential – but several dynamics have a huge impact on productivity.

2491
 
Explorer Emphasis Article

Who’s got the last laugh now? The Uteland Butte once was a sandstone that operators quickly passed through – and often ignored – on their way to other targets. But things are changing in Utah.

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In-Person Training
Midland Texas United States 14 January, 2015 14 January, 2015 13531
 
Midland, Texas, United States
14 January 2015

The Midland Playmaker Forum is focused on new and emerging plays of interest to sections or regions, with a broad global appeal to explorers in all locations. Its emphasis is the process of turning a prospect into a discovery and therefore complements the existing prospect expos.

Oklahoma City Oklahoma United States 19 February, 2015 19 February, 2015 11378
 
Oklahoma City, Oklahoma, United States
19 February 2015

This year’s Mississippian Lime Forum unleashes science, technology, and experience to solve persistent puzzles, and dramatically improve economics. Consider 2015 a breakthrough year as new, sometimes controversial new techniques and technologies are being implemented for the first time.

London United Kingdom 09 March, 2015 10 March, 2015 13537
 
London, United Kingdom
9-10 March 2015

The London Playmaker Forum is focused on new and emerging plays of interest to sections or regions, with a broad global appeal to explorers in all locations. Its emphasis is the process of turning a prospect into a discovery and therefore complements the existing prospect expos.

Austin Texas United States 21 April, 2015 23 April, 2015 1518
 
Austin, Texas, United States
21-23 April 2015

The overall goal of this course is to provide tools for efficient and effective re-exploration and development. It uses a two-part approach. First it uses petrophysical analysis to understand all that can be derived from examination of standard open-hole logs. This is followed by integrated approaches to discover key factors controlling oil and gas distribution in carbonate reservoirs in the greater Midcontinent USA. Methodologies and workflows reviewed include geosteering and evaluation of horizontal wells and optimizing carbon storage utilization and management.

Las Negras Spain 08 June, 2015 13 June, 2015 31
 
Las Negras, Spain
8-13 June 2015

The field seminar develops and evaluates the sequence stratigraphic framework and controls on location and reservoir character of Upper Miocene-Pliocene carbonate sequences from a variety of carbonate systems within the context of the regional paleogeography.

Casper Wyoming United States 24 August, 2015 28 August, 2015 1513
 
Casper, Wyoming, United States
24-28 August 2015

Take advantage of this unique opportunity to learn all the aspects related to the understanding and modeling of fractured reservoirs. Attendees will take geologic concepts and use them in reservoir modeling through hands-on sessions devoted to the examination of outcrop, core and log data. They will use that information and a software to create 3D fractured reservoir models. Using actual Teapot Dome (Wyoming, USA) field data from the Tensleep and Niobrara Shale formations and a hands-on approach, the workshop allows the geoscientist to identify fractures and to construct predictive 3D fracture models that can be used to identify productive zones, plan wells and to create fracture porosity and permeability models for reservoir simulation.

Salt Lake City Utah United States 20 September, 2015 27 September, 2015 151
 
Salt Lake City, Utah, United States
20-27 September 2015

Participants will learn a specific and comprehensive methodology for finding and developing conventional and unconventional oil and gas resources associated with lake deposits. The seminar will start with the Quaternary Bonneville basin in Utah, to build familiarity with lacustrine depositional processes. Participants then examine world-famous exposures of organic-rich mudstone, fluvial sandstone, and carbonate microbialite facies in Wyoming.

Naples Italy 26 September, 2015 02 October, 2015 36
 
Naples, Italy
26 September - 2 October 2015

The main part of the field seminar will focus on the description of the fractured carbonates and the extrapolation from the outcrop observations to the subsurface for building geologically plausible reservoir models.

14 February, 3000 14 February, 3000 7812
 
14 February, 3000 14 February, 3000 7816
 
14 February, 3000 14 February, 3000 7815
 
Online Training
01 January, 2013 01 January, 9999 1459
 
1 January 2013 - 1 January 9999

There are more approximately 1,000 oil and gas fields in the world that have been classified as "giant," containing more than 500 million barrels of recoverable oil and /or 3 trillion cubic feet of gas.

24 October, 2013 24 October, 2013 1499
 
24 October 2013

This e-symposium will be introducing signal processing techniques as a means to maximize extracting geomechanical data from petrophysical logs.

10 November, 2011 10 November, 2011 1481
 
10 November 2011

This work investigates how heterogeneity can be defined and how we can quantify this term by describing a range of statistical heterogeneity (e.g. coefficient of variation and the Lorenz coefficient).

07 June, 2012 07 June, 2012 1488
 
7 June 2012

Unger Field, discovered in1955, has produced 8.6 million barrels of oil from a thinly (several ft) bedded, locally cherty dolomite containing vuggy and intercrystalline porosity.

30 August, 2012 30 August, 2012 1489
 
30 August 2012

The entire Middle Pennsylvanian–to–top Precambrian basement (500 m) interval was cored in early 2011 in the BEREXCO Wellington KGS #1-32 well in Wellington Field, Sumner County, KS.

21 February, 2013 21 February, 2013 1495
 
21 February 2013

The course will review core data, petrophysical comparisons, rock physics modeling (including pseudo logs and mechanical properties).

28 April, 2011 28 April, 2011 1471
 
28 April 2011

The Niobrara Petroleum System of the U.S. Rocky Mountain Region is a major tight petroleum resource play.

11 November, 2010 11 November, 2010 1465
 
11 November 2010

This e-symposium is ideal for geologists, geophysicists, engineers and other geoscientists who are involved in gas shale exploration and production.

14 February, 3000 14 February, 3000 7817
 
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