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"Breakthrough elegance": ExxonMobil geologists Jeff Ottmann and Kevin Bohacs shared their highly-coveted knowledge on sweet spots and producibility thresholds at a recent Geosciences Technology Workshop on Unconventional Reservoir Quality.

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This article describes a 250-m (820-ft)-thick upper Eocene deep-water clastic succession. This succession is divided into two reservoir zones: the lower sandstone zone (LSZ) and the upper sandstone zone, separated by a package of pelitic rocks with variable thickness on the order of tens of meters. The application of sequence-stratigraphic methodology allowed the subdivision of this stratigraphic section into third-order systems tracts.

The LSZ is characterized by blocky and fining-upward beds on well logs, and includes interbedded shale layers of as much as 10 m (33 ft) thick. This zone reaches a maximum thickness of 150 m (492 ft) and fills a trough at least 4 km (2 mi) wide, underlain by an erosional surface. The lower part of this zone consists of coarse- to medium-grained sandstones with good vertical pressure communication. We interpret this unit as vertically and laterally amalgamated channel-fill deposits of high-density turbidity flows accumulated during late forced regression. The sandstones in the upper part of this trough are dominantly medium to fine grained and display an overall fining-upward trend. We interpret them as laterally amalgamated channel-fill deposits of lower density turbidity flows, relative to the ones in the lower part of the LSZ, accumulated during lowstand to early transgression.

The pelitic rocks that separate the two sandstone zones display variable thickness, from 35 to more than 100 m (115–>328 ft), indistinct seismic facies, and no internal markers on well logs, and consist of muddy diamictites with contorted shale rip-up clasts. This section is interpreted as cohesive debris flows and/or mass-transported slumps accumulated during late transgression.

The upper sandstone zone displays a weakly defined blocky well-log signature, where the proportion of sand is higher than 80%, and a jagged well-log signature, where the sand proportion is lower than 60%. The high proportions of sand are associated with a channelized geometry that is well delineated on seismic amplitude maps. Several depositional elements are identified within this zone, including leveed channels, crevasse channels, and splays associated with turbidity flows. This package is interpreted as the product of increased terrigenous sediment supply during highstand normal regression.

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Numerous studies of sediment-dispersal systems have focused on the relative role of allogenic versus autogenic controls, and their stratigraphic imprint. Advancing our understanding of these vital issues depends heavily on geochronology.

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The Gulf of Mexico (GOM) is the 9th largest body of water on earth, covering an area of approximately 1.6 million km2 with water depths reaching 4,400 m (14,300’). The basin formed as a result of crustal extension during the early Mesozoic breakup of Pangaea. Rifting occurred from the Late Triassic to early Middle Jurassic. Continued extension through the Middle Jurassic combined with counter-clockwise rotation of crustal blocks away from North America produced highly extended continental crust in the subsiding basin center. Subsidence eventually allowed oceanic water to enter from the west leading to thick, widespread, evaporite deposition. Seafloor spreading initiated in the Late Jurassic eventually splitting the evaporite deposits into northern (USA) and southern (Mexican) basins. Recent work suggests that this may have been accomplished by asymmetric extension, crustal delamination, and exposure of the lower crust or upper mantle rather than true sea floor spreading (or it could be some combination of the two). By 135 Ma almost all extension had ceased and the basic configuration of the GOM basin seen today was established. The Laramide Orogeny was the last major tectonic event impacting the GOM. It caused uplift and erosion for the NW margin from the Late Cretaceous to early Eocene.

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Criteria for recognizing stratigraphic sequences are well established on continental margins but more challenging to apply in basinal settings. We report an investigation of the Upper Devonian Woodford Shale, Permian Basin, west Texas based on a set of four long cores, identifying sea level cycles and stratigraphic sequences in an organic-rich shale.

The Woodford Shale is dominated by organic-rich mudstone, sharply overlain by a bioturbated organic-poor mudstone that is consistent with a second-order eustatic sea level fall. Interbedded with the organic-rich mudstone are carbonate beds, chert beds, and radiolarian laminae, all interpreted as sediment gravity-flow deposits. Bundles of interbedded mudstone and carbonate beds alternate with intervals of organic-rich mudstone and thin radiolaria-rich laminae, defining a 5–10 m (16–33 ft)-thick third-order cyclicity. The former are interpreted to represent highstand systems tracts, whereas the latter are interpreted as representing falling stage, lowstand, and transgressive systems tracts. Carbonate beds predominate in the lower Woodford section, associated with highstand shedding at a second-order scale; chert beds predominate in the upper Woodford section, responding to the second-order lowstand.

Additional variability is introduced by geographic position. Wells nearest the western margin of the basin have the greatest concentration of carbonate beds caused by proximity to a carbonate platform. A well near the southern margin has the greatest concentration of chert beds, resulting from shedding of biogenic silica from a southern source. A well in the basin center has little chert and carbonate; here, third-order sea level cycles were primarily reflected in the stratigraphic distribution of radiolarian-rich laminae.

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This article introduces a new set of seismic attributes that play an important role in extracting detailed stratigraphic information from seismic data.

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Sequence stratigraphy and coal cycles based on accommodation trends were investigated in the coal-bearing Lower Cretaceous Mannville Group in the Lloydminster heavy oil field, eastern Alberta. The study area is in a low accommodation setting on the cratonic margin of the Western Canada sedimentary basin. Geophysical log correlation of coal seams, shoreface facies, and the identification of incised valleys has produced a sequence-stratigraphic framework for petrographic data from 3 cored and 115 geophysical-logged wells. Maceral analysis, telovitrinite reflectance, and fluorescence measurements were taken from a total of 206 samples. Three terrestrial depositional environments were interpreted from the petrographic data: ombrotrophic mire coal, limnotelmatic mire coal, and carbonaceous shale horizons. Accommodation-based coal (wetting- and drying-upward) cycles represent trends in depositional environment shifts, and these cycles were used to investigate the development and preservation of the coal seams across the study area.

The low-accommodation strata are characterized by a high-frequency occurrence of significant surfaces, coal seam splitting, paleosol, and incised-valley development. Three sequence boundary unconformities are identified in only 20 m (66 ft) of strata. Coal cycle correlations illustrate that each coal seam in this study area was not produced by a single peat-accumulation episode but as an amalgamation of a series of depositional events. Complex relations between the Cummings and Lloydminster coal seams are caused by the lateral fragmentation of strata resulting from the removal of sediment by subaerial erosion or periods of nondeposition. Syndepositional faulting of the underlying basement rock changed local accommodation space and increased the complexity of the coal cycle development.

This study represents a low-accommodation example from a spectrum of stratigraphic studies that have been used to establish a terrestrial sequence-stratigraphic model. The frequency of changes in coal seam quality is an important control on methane distribution within coalbed methane reservoirs and resource calculations in coal mining. A depositional model based on the coal cycle correlations, as shown by this study, can provide coal quality prediction for coalbed methane exploration, reservoir completions, and coal mining.

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New dimensions: Geoscientists study how 3-D views of Eagle Ford outcrops are a great tool.

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A new hierarchical architectural classification for clastic marginal-marine depositional systems is presented and illustrated with examples. In ancient rocks, the architectural scheme effectively integrates the scales of sedimentology (core, outcrop) and sequence stratigraphy (wireline-log correlation, reflection seismic). The classification also applies to modern sediments, which allows for direct comparison of architectural units between modern and ancient settings. In marginal-marine systems, the parasequence typically defines reservoir flow units. This classification addresses subparasequence scales of stratigraphy that commonly control fluid flow in these reservoirs. The scheme consists of seven types of architectural units that are placed on five architectural hierarchy levels: hierarchy level I: element (E) and element set (ES); hierarchy level II: element complex (EC) and element complex set (ECS); hierarchy level III: element complex assemblage (ECA); hierarchy level IV: element complex assemblage set (ECAS); and hierarchy level V: transgressive-regressive sequence (T-R sequence). Architectural units in levels I to III are further classified relative to dominant depositional processes (wave, tide, and fluvial) acting at the time of deposition. All architectural units are three-dimensional and can also be expressed in terms of plan-view and cross-sectional geometries. Architectural units can be linked using tree data structures by a set of familial relationships (parent-child, siblings, and cousins), which provides a novel mechanism for managing uncertainty in marginal-marine systems. Using a hierarchical scheme permits classification of different data types at the most appropriate architectural scale. The use of the classification is illustrated in ancient settings by an outcrop and subsurface example from the Campanian Bearpaw–Horseshoe Canyon Formations transition, Alberta, Canada, and in modern settings, by the Mitchell River Delta, northern Australia. The case studies illustrate how the new classification can be used across both modern and ancient systems, in complicated, mixed-process depositional environments.
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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.
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In-Person Training
Bucharest Romania 17 May, 2016 18 May, 2016 28757 Desktop /Portals/0/PackFlashItemImages/WebReady/ExxonMobil-Student-Workshop.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Student, Sedimentology and Stratigraphy, Sequence Stratigraphy, Geophysics, Seismic, Reservoir Characterization, Engineering, Seismic Attributes, Clastics, Marine, Petrophysics and Well Logs
Bucharest, Romania
17-18 May 2016
This course is designed to teach advanced students the principles, concepts and application of sequence stratigraphy as applied to siliciclastic facies in non-marine, shallow marine, and deep water environments.
Three Forks Montana United States 23 May, 2016 25 May, 2016 13422 Desktop /Portals/0/PackFlashItemImages/WebReady/hero-lodgepole-bakken-petroleum-system.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Sedimentology and Stratigraphy, Petrophysics and Well Logs, Geochemistry and Basin Modeling, Source Rock, Sequence Stratigraphy
Three Forks, Montana, United States
23-25 May 2016

This field seminar will give participants an overview about the geology, reservoir engineering and operation aspects of the Lodgepole-Bakken-Three Forks Petroleum System.  Excellent outcrops illustrate how facies, reservoir properties and rock strength can vary along a lateral well bore. Engineers, geologists and operators will find this especially interesting.

Calgary Alberta Canada 18 June, 2016 19 June, 2016 23869 Desktop /Portals/0/PackFlashItemImages/WebReady/wiki-biostratigraphy-in-sequence-stratigraphy-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Member, Student, Short Courses, Conventions, Pre-Convention, Sedimentology and Stratigraphy, Sequence Stratigraphy
Calgary, Alberta, Canada
18-19 June 2016

This course is designed to teach graduate students the principles, concepts and methods of sequence stratigraphy. Sequence stratigraphy is an informal chronostratigraphic methodology that uses stratal surfaces to subdivide the stratigraphic record. This methodology allows the identification of coeval facies, documents the time-transgressive nature of classic lithostratigraphic units and provides geoscientists with an additional way to analyze and subdivide the stratigraphic record.

Calgary Alberta Canada 18 June, 2016 19 June, 2016 23863 Desktop /Portals/0/PackFlashItemImages/WebReady/sc-basin-analysis-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Member, Student, Sedimentology and Stratigraphy, Sequence Stratigraphy, Reservoir Characterization, Engineering, 3D Seismic, Seismic Attributes
Calgary, Alberta, Canada
18-19 June 2016

This course reviews the basin analysis methods and workflows used in oil and gas exploration, with special emphasis on the integration of geologic, geophysical and geochemical data. The workflows are built on three main disciplines: sedimentology, sequence stratigraphy and seismic geomorphology. Logs and 2-D/3-D seismic will be used to characterize clastic and carbonate depositional systems through time and space in the principal sedimentary basin types, including extensional basins (rifts, growth fault margins and passive margins), foreland basins and confined basins associated with mud and salt diapirism.

Calgary Alberta Canada 18 June, 2016 18 June, 2016 23817 Desktop /Portals/0/PackFlashItemImages/WebReady/sc7-ace16-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Member, Student, Short Courses, Conventions, Pre-Convention, Sedimentology and Stratigraphy, Sequence Stratigraphy
Calgary, Alberta, Canada
18 June 2016

This workshop combines interactive lectures and exercises addressing the expression of depositional sequences in mudstones on seismic, well-log, core and outcrop data. Examples include the New Albany Shale, Barnett Shale, Shublik Formation, Kimmeridge Formation, Kingak Formation, Hue Shale, Mowry Shale and Monterey Formation. Participants will practice recognition and correlation of significant stratigraphic packages through seismic stratigraphy, stacking pattern analysis of well-log, core and outcrop data, shale sedimentology, thin-section and geochemical data.

Calgary Alberta Canada 23 June, 2016 25 June, 2016 23973 Desktop /Portals/0/PackFlashItemImages/WebReady/ACE-2016-FT-14-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Field Trips, Conventions, Post-Convention, Sedimentology and Stratigraphy, Sequence Stratigraphy
Calgary, Alberta, Canada
23-25 June 2016

This two and a half day post-convention field trip will examine Upper Devonian (Frasnian) shallow water carbonate platform and time equivalent basinal strata (Winterburn, Woodbend and Beaverhill Lake Groups subsurface) at a number of well exposed outcrops in the Main and Front Ranges of West Central Alberta.

Lagos Nigeria 11 July, 2016 13 July, 2016 21922 Desktop /Portals/0/PackFlashItemImages/WebReady/sequence-stratigraphy-concepts-principles-applications-clastic-depositional-environments-02feb-2016-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Engineering, Reservoir Characterization, Geochemistry and Basin Modeling, Source Rock, Petrophysics and Well Logs, Sedimentology and Stratigraphy, Clastics, Conventional Sandstones, Deep Sea / Deepwater, Deepwater Turbidites, Eolian Sandstones, Estuarine Deposits, Fluvial Deltaic Systems, High Stand Deposits, Incised Valley Deposits, Lacustrine Deposits, Low Stand Deposits, Marine, Regressive Deposits, Sheet Sand Deposits, Shelf Sand Deposits, Slope, Transgressive Deposits, Sequence Stratigraphy, Deep Basin Gas, Diagenetic Traps, Stratigraphic Traps, Structural Traps
Lagos, Nigeria
11-13 July 2016
Sequence stratigraphy provides a framework for the integration of geological, geophysical, biostratigraphic and engineering data, with the aim of predicting the distribution of reservoir, source rock and seal lithologies. It gives the geoscientist a powerful predictive tool for regional basin analysis, shelf-to-basin correlation, and characterization of reservoir heterogeneity. This course will examine the underlying geological principles, processes and terminology related to sequence stratigraphic interpretation. The strength of this course is the application of these basic principles to subsurface datasets in a series of well-founded exercises.
Grand Junction Colorado United States 28 September, 2016 05 October, 2016 86 Desktop /Portals/0/PackFlashItemImages/WebReady/fs-sedimentology-and-sequence-stratigraphic-response-of-paralic-deposits.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Sedimentology and Stratigraphy, Clastics, Sequence Stratigraphy, Fluvial Deltaic Systems, Estuarine Deposits, Marine, Incised Valley Deposits, High Stand Deposits, Low Stand Deposits, Petrophysics and Well Logs
Grand Junction, Colorado, United States
28 September - 5 October 2016

Participants will learn through the use of spectacular outcrops, subsurface datasets, and stratigraphic modeling how these systems tracts and key surfaces (flooding surfaces and sequence boundaries) may be recognized.

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
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