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Bulletin Article


Diagenesis significantly impacts mudstone lithofacies. Processes operating to control diagenetic pathways in mudstones are poorly known compared to analogous processes occurring in other sedimentary rocks. Selected organic-carbon-rich mudstones, from the Kimmeridge Clay and Monterey Formations, have been investigated to determine how varying starting compositions influence diagenesis.


Umiat field in northern Alaska is a shallow, light-oil accumulation with an estimated original oil in place of more than 1.5 billion bbl and 99 bcf associated gas. The field, discovered in 1946, was never considered viable because it is shallow, in permafrost, and far from any infrastructure. Modern drilling and production techniques now make Umiat a more attractive target if the behavior of a rock, ice, and light oil system at low pressure can be understood and simulated.

The Umiat reservoir consists of shoreface and deltaic sandstones of the Cretaceous Nanushuk Formation deformed by a thrust-related anticline. Depositional environment imparts a strong vertical and horizontal permeability anisotropy to the reservoir that may be further complicated by diagenesis and open natural fractures.

Experimental and theoretical studies indicate that there is a significant reduction in the relative permeability of oil in the presence of ice, with a maximum reduction when connate water is fresh and less reduction when water is saline. A representative Umiat oil sample was reconstituted by comparing the composition of a severely weathered Umiat fluid to a theoretical Umiat fluid composition derived using the Pedersen method. This sample was then used to determine fluid properties at reservoir conditions such as bubble point pressure, viscosity, and density.

These geologic and engineering data were integrated into a simulation model that indicate recoveries of 12%–15% can be achieved over a 50-yr production period using cold gas injection from five well pads with a wagon-wheel configuration of multilateral wells.


The presence of hydrocarbon-bearing sandstones within the Eocene of the Forties area was first documented in 1985, when a Forties field (Paleocene) development well discovered the Brimmond field. Further hydrocarbons in the Eocene were discovered in the adjacent Maule field in 2009. Reservoir geometry derived from three-dimensional seismic data has provided evidence for both a depositional and a sand injectite origin for the Eocene sandstones. The Brimmond field is located in a deep-water channel complex that extends to the southeast, whereas the Maule field sandstones have the geometry of an injection sheet on the updip margin of the Brimmond channel system with a cone-shape feature emanating from the top of the Forties Sandstone Member (Paleocene). The geometry of the Eocene sandstones in the Maule field indicates that they are intrusive and originated by the fluidization and injection of sand during burial. From seismic and borehole data, it is unclear whether the sand that was injected to form the Maule reservoir was derived from depositional Eocene sandstones or from the underlying Forties Sandstone Member. These two alternatives are tested by comparing the heavy mineral and garnet geochemical characteristics of the injectite sandstones in the Maule field with the depositional sandstones of the Brimmond field and the Forties sandstones of the Forties field.

The study revealed significant differences between the sandstones in the Forties field and those of the Maule and Brimmond fields), both in terms of heavy mineral and garnet geochemical data. The Brimmond-Maule and Forties sandstones therefore have different provenances and are genetically unrelated, indicating that the sandstones in the Maule field did not originate by the fluidization of Forties sandstones. By contrast, the provenance characteristics of the depositional Brimmond sandstones are closely comparable with sandstone intrusions in the Maule field. We conclude that the injectites in the Maule field formed by the fluidization of depositional Brimmond sandstones but do not exclude the important function of water from the huge underlying Forties Sandstone Member aquifer as the agent for developing the fluid supply and elevating pore pressure to fluidize and inject the Eocene sand. The study has demonstrated that heavy mineral provenance studies are an effective method of tracing the origin of injected sandstones, which are increasingly being recognized as an important hydrocarbon play.


Interpretation of seismic data from the Sorvestsnaget Basin, southwest Barents Sea, demonstrates gradual middle Eocene basin infilling (from the north) generated by southward-prograding shelf-margin clinoforms. The basin experienced continued accommodation development during the middle Eocene because of differential subsidence caused by the onset of early Eocene sea-floor spreading in the Norwegian-Greenland Sea, faulting, salt movement, and different tectonic activity between the Sorvestsnaget Basin and Veslemoy high. During this time, the margin shows transformation from an initially high-relief margin to a progradation in the final stage. The early stage of progradation is characterized by the establishment of generally oblique clinoform shifts creating a flat shelf-edge trajectory that implies a gentle falling or stable relative sea level and low accommodation-to-sediment supply ratio (lt1) in the topsets. During the early stage of basin development, the high-relief margin, narrow shelf, stable or falling relative sea level, seismicity, and presumably high sedimentation rate caused accumulation of thick and areally extensive deep-water fans. Seismic-scale sandstone injections deform the fans.

A fully prograding margin developed when the shelf-to-basin profile lowered, apparently because of increased subsidence of the northern part. This stage of the basin development is generally characterized by the presence of sigmoid clinoform shifts creating an ascending shelf-edge trajectory that is implying steady or rising relative sea level with an accommodation-to-sediment supply ratio of greater than 1, implying sand accumulation on the shelf. This study suggests that some volume of sand was transported into the deep water during relative sea level rise considering the narrow shelf and inferred high rates of sediment supply.

Organic-carbon–rich shales of the lower Marcellus Formation were deposited at the toe and basinward of a prograding clinothem associated with a Mahantango Formation delta complex centered near Harrisburg, Pennsylvania. Distribution of these organic-carbon–rich shales was influenced by shifts in the delta complex driven by changes in rates of accommodation creation and by a topographically high carbonate bank that formed along the Findlay-Algonquin arch during deposition of the Onondaga Formation. Specifically, we interpret the Union Springs member (Shamokin Member of the Marcellus Formation) and the Onondaga Formation as comprising a single third-order depositional sequence. The Onondaga Formation was deposited in the lowstand to transgressive systems tract, and the Union Springs member was deposited in the transgressive, highstand, and falling-stage systems tract. The regional extent of parasequences, systems tracts, and the interpreted depositional sequence suggest that base-level fluctuations were primarily caused by allogenic forcing—eustasy, climate, or regional thermal uplift or subsidence—instead of basement fault reactivation as argued by previous workers. Paleowater depths in the region of Marcellus Formation black mudrock accumulation were at least 330 ft (100 m) as estimated by differences in strata thickness between the northwestern carbonate bank and basinal facies to the southeast. Geochemical analysis indicates anoxic to euxinic bottom-water conditions. These conditions were supported by a deep, stratified basin with a lack of circulation.
We use three-dimensional seismic reflection data and new map-based structural restoration methods to define the displacement history and characteristics of a series of tear faults in the deep-water Niger Delta. Deformation in the deep-water Niger Delta is focused mostly within two fold-and-thrust belts that accommodate downdip shortening produced by updip extension on the continental shelf. This shortening is accommodated by a series of thrust sheets that are locally cut by strike-slip faults. Through seismic mapping and interpretation, we resolve these strike-slip faults to be tear faults that share a common detachment level with the thrust faults. Acting in conjunction, these structures have accommodated a north –south gradient in westward-directed shortening. We apply a map-based restoration technique implemented in Gocad to restore an upper stratigraphic horizon of the late Oligocene and use this analysis to calculate slip profiles along the strike-slip faults. The slip magnitudes and directions change abruptly along the lengths of the tear faults as they interact with numerous thrust sheets. The discontinuous nature of these slip profiles reflects the manner in which they have accommodated differential movement between the footwall and hanging-wall blocks of the thrust sheets. In cases for which the relationship between a strike-slip fault and multiple thrust faults is unclear, the recognition of this type of slip profile may distinguish thin-skinned tear faults from more conventional deep-seated, throughgoing strike-slip faults.

Bulletin E P Note


The petroleum trap for the Athabasca oil sands has remained elusive because it was destroyed by flexural loading of the Western Canada Sedimentary Basin during the Late Cretaceous and Paleocene. The original trap extent is preserved because the oil was biodegraded to immobile bitumen as the trap was being charged during the Late Cretaceous. Using well and outcrop data, it is possible to reconstruct the Cretaceous overburden horizons beyond the limit of present-day erosion. Sequential restoration of the reconstructed horizons reveals a megatrap at the top of the Wabiskaw-McMurray reservoir in the Athabasca area at 84 Ma (late Santonian). The megatrap is a four-way anticline with dimensions 285 x 125 km (177 x 78 mi) and maximum amplitude of 60 m (197 ft). The southeastern margin of the anticline shows good conformance to the bitumen edge for 140 km (87 mi). To the northeast of the anticline, bitumen is present in a shallower trap domain in what is interpreted to be an onlap trap onto the Canadian Shield; leakage along the onlap edge is indicated by tarry bitumen outliers preserved in basement rocks farther to the northeast. Peripheral trap domains that lie below the paleospillpoint, in northern, southern, and southwestern Athabasca, and Wabasca, are interpreted to represent a late charge of oil that was trapped by bitumen already emplaced in the anticline and the northeastern onlap trap. This is consistent with kimberlite intrusions containing live bitumen, which indicate that the northern trap domain was charged not before 78 Ma. The trap restoration has been tested using bitumen-water contact well picks. The restored picks fall into groups that are consistent both with the trap domains determined from the top reservoir restoration and the conceptual charge model in which the four-way anticline was filled first, followed by the northeastern onlap trap, and then the peripheral trap domains.

Bulletin Geologic Note


Offshore sequences of volcaniclastic rocks (such as hyaloclastite deposits) are poorly understood in terms of their rock properties and their response to compaction and burial. As petroleum exploration targets offshore volcanic rifted margins worldwide, understanding of volcanic rock properties becomes important both in terms of drilling and how the rocks may behave as seals, reservoirs, or permeability pathways. The Hawaiian Scientific Drilling Project phase II in 2001 obtained a 3 km-(2-mi)-long core of volcanic and volcaniclastic rocks that records the emergence of the largest of the Hawaiian islands. Core recovery of 2945 m (9662 ft) resulted in an unparalleled data set of volcanic and volcaniclastic rocks. Detailed logging, optical petrology, and major element analysis of two sections at depths 1831–1870 and 2530–2597 m (6007–6135 and 8300–8520 ft) are compared to recovered petrophysical logs (gamma ray, resistivity, and P-wave velocity). This study concludes deviation in petrophysical properties does not seem to correlate to changes in grain size or clast sorting, but instead correlates with alteration type (zeolite component) and bulk mineralogy (total olivine phenocryst percentage component). These data sets are important in helping to calibrate well-log responses through hyaloclastite intervals in areas of active petroleum exploration such as the North Atlantic (e.g., Faroe-Shetland Basin, United Kingdom, and Faroe Islands, the Norwegian margin and South Atlantic margins bordering Brazil and Angola).

Environmental Geosciences Article

We use sediment ages and mercury (Hg) concentrations to estimate past and future concentrations in the South River, Virginia, where Hg was released between 1930 and 1950 from a manufacturing process related to nylon production. In a previous study, along a 40 km (25 mi) reach, samples were collected from 26 of 54 fine-grained deposits that formed in the lee of large wood obstructions in the channel and analyzed for grain size, Hg concentration, and organic content. We also obtained radiometric dates from six deposits. To create a history that reflects the full concentration distribution (which contains concentrations as high as 900 mg/kg [900 ppm]), here, we treat the deposits as a single reservoir exchanging contaminated sediments with the overlying water column, and assume that the total sediment mass in storage and the distribution of sediment ages are time invariant. We use reservoir theory to reconstruct the annual history of Hg concentration on suspended sediment using data from our previous study and new results presented here. Many different reconstructed histories fit our data. To constrain results, we use information from a well-preserved core (and our estimate of the total mass of Hg stored in 2007) to specify the years associated with the peak concentration of 900 mg/kg. Our results indicate that around 850 kg (1874 lb) of Hg was stored in the deposits between 1955 and 1961, compared to only 80 kg (176 lb) today. Simulations of future Hg remediation suggest that 100-yr timescales will be needed for the South River to remove Hg-contaminated sediments from the channel perimeter through natural processes.

 SONAR, historical and aerial photographs, and vibracoring were used to assess the type and thickness distribution of sediments impounded by Gold Ray Dam on the Rogue River in southern Oregon. From these data, a volume of about 400,000 cubic yards (

Equation EG13006eq1

) of sediment was determined for the inundated area of the reservoir.

Overall, sediment volumes in the impounded part of the reservoir were less than expected. There are three possibilities that may explain the perceived absence of sediment: (1) the gradient of the Rogue River in this stretch is less, and therefore sediment yields are less; (2) the extraction of gravels and/or other impediments upstream decreased the availability of sediments delivered into the reservoir; and/or (3) sediment was deposited by a prograding delta that filled in the inundated area of the floodplain upstream from Gold Ray Dam. The amount of sediment deposited on this inundated floodplain may have been as much as 1,800,000 cubic yards (Equation EG13006eq2), bringing the total amount of sediment impounded by Gold Ray Dam to Equation EG13006eq3 yards (Equation EG13006eq4).

Applied sedimentology is not only vital to developing a depositional model for the filling of a reservoir, but also providing insights into depositional and erosional changes that will occur upon the removal of a dam. In particular, the processes of delta formation, reoccupation of abandoned channels, and avulsion are paramount in determining sediment accumulation and distribution in reservoirs.

Recently Added in News

Explorer Article

Explorer Article

The ability to analyze and evaluate oil and gas exploration just got easier. A Web-based search-and-retrieval tool can now give subscribers the ability to find hundreds of thousands of geological maps, cross-sections, tables and other “exploration objects” faster and more easily and quicker than ever before. It’s called Database Exploration Objects (DEO), it was designed by AAPG Datapages, and it’s up and ready.


The second annual Unconventional Resources Technology Conference, which once again threw a multidiscipline spotlight on new approaches, technology and science being used to develop unconventional plays, attracted more than 5,000 attendees– a 25 percent increase over last year’s inaugural event – to Denver’s Colorado Convention Center in late August.

Explorer Director’s Corner


As this issue of EXPLORER goes to print, geoscience students and industry recruiters are gathering on the plains of Wyoming for the Rocky Mountain Rendezvous, the annual job fair of AAPG’s Rocky Mountain Section.

Explorer Division Column DPA


As AAPG Division of Professional Affairs president I am often asked, “What is the DPA’s purpose?” I decided one of the best ways to answer this question is take the Letterman approach with a Top 10 list of purposes and reasons to be part of DPA.

Explorer Foundation Update

Explorer Foundation Update

It has a new name, a new energy and a new lineup of experts, all primed to spread geoscience knowledge around the world. “It” is AAPG’s newly named Global Distinguished Lecture Program – emphasis on the “global” – which dates back to 1941 but continues to be the Association’s flagship initiative for offering the latest in geologic science to AAPG affiliated geological societies and universities.

Explorer Geophysical Corner

Explorer Geophysical Corner

Seismic data are usually contaminated with noise, which refers to any unwanted features in the data. These unwanted features may actually be somebody else’s signal, such as converted waves in what we think of as “P-wave” data – but more commonly, these unwanted “noise” features provide little or no information about the subsurface, and are referred to as random noise and coherent noise.

Explorer Historical Highlight


The Toyokawa field is a small oil field, covering an area of about six square kilometers, located in northeastern Japan’s Akita Prefecture. The hillock area where the Toyokawa oil field is situated formerly was covered with natural asphalt (tar) deposits that had erupted from the subsurface. The current scenery resembles the famous La Brea Tar Pit in Los Angeles.

Explorer Policy Watch

Explorer Policy Watch

Ronald Reagan stated in an April 2, 1988, radio address that “ … although basic research does not begin with a particular practical goal, when you look at the results over the years it ends up being one of the most practical things government does.” This widely held opinion has been notoriously hard to verify or quantify, leading to questions about appropriate funding levels.

Explorer President’s Column


I find it ironic that George Mitchell, the “father of hydraulic fracturing technology” (aka, “father of fracing”), a technology that so many people fear or hate because of its perceived negative environmental impact, was so passionate about the environment and sustainability. This is a message we need to convey.

Explorer Regions and Sections


AAPG held its first conference in Myanmar in August. The technical program titled “Tectonic Evolution of Myanmar and its Basin Development with Special References to its Petroleum Occurrences” was attended by 238 local and international delegates from 16 countries.

Recently Added Special Publications



Written in accessible language, this publication is a comprehensive overview of NGLs from production in the oil patch to consumption in the fuel and petrochemical industries.


The contributions in this volume are valuable in providing the impetus to recognize, quantitatively characterize, and implement reservoir development and management practices that take these important reservoir elements into account.


This special issue honors the legacy of J. Fred Read, a pioneer in carbonate sedimentology and stratigraphy. He taught at Virginia Tech for 38 years and, along with his students, published more than 120 papers. Many of these students have become leaders in carbonate research.


This innovative lab book provides a unified methodology for problem solving in structural geology using linear algebra and computation.


This is the first book to systematically cover the conceptual framework of the discipline and the wide breadth of applications in both paleobiology and sedimentology, bridging the gap between the two main facets of the field. It emphasizes the importance of understanding ecological controls on benthic fauna distribution and the role of burrowing organisms in changing their environments.


Norman Hyne's comprehensive upstream dictionary has been thorougly updated, with more than 8,000 new definitions and entries. Covering everything in the upstream oil and gas sector, this new second edition also covers land, legal, accounting and finance terms.




These proceedings contain 283 manuscripts and extended abstracts presented during the three days of plenary, ePaper and oral sessions and are stored conveniently on a 4GB flash drive. The content is a product of the joint venture between AAPG, SEG and SPE and the collaboration of key disciplines and technologies engaged in the development of North American resource plays.


Giant Oil and Gas Fields of the Decade: 1990-1999 is the fourth of a four-decade series of Memoirs commemorating important giant discoveries. This title presents major trends that characterized giant-field discoveries in the 1990s and includes tectonic and sedimentary-basin maps.

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Wiki Article


Deltaic depositional facies result from interacting dynamics processes (wave energy, tidal regime, currents, climate, etc.), which modify and disperse riverborne (fluvial) clastic deposits.


Sequence stratigraphy is the study of genetically related facies within a framework of chronostratigraphically significant surfaces. Paleontologic data, integrated with seismic and well log data, are an integral part of sequence stratigraphic analysis.


Pore type, pore geometry, and fluid properties are critical factors affecting permeability. Sandstone texture directly affects pore type and geometry. Knowing what textures and fluids to expect, as well as what authigenic clays might be present, can help us predict permeability


Solar energy is the use of direct sunlight, the solar energy arriving on Earth. Direct sunlight can be used for two main purposes: for heating and cooling and for the generation of electricity.


Seismic facies analysis is the description and interpretation of seismic reflection parameters, such as configuration, continuity, amplitude, and frequency, within the stratigraphic framework of a depositional sequence.


Coal is a readily combustible rock containing more than 50% by weight and more than 70% by volume of carbonaceous material, including inherent moisture.


Hydroelectric power is, as of 2005, the second largest source of electricity in the world (18%) after coal, which supplies about 38%, but ahead of nuclear power, natural gas, and oil, which contribute 17, 16, and 10%, respectively, of the total generated electricity.


An oil shale is defined as a fine-grained sedimentary rock that contains a high proportion of endogenous organic matter (kerogen) mostly insoluble in ordinary petroleum solvents, from which substantial amounts of synthetic oil and/or gas can be extracted by heating it to a sufficiently high temperature, a process called retorting. Oil shales have a low calorific value and high ash and mineral content.


Gas hydrates (also called gas clathrates) are icelike, crystalline solids composed of natural-gas molecules, principally methane, trapped in rigid crystalline cages formed by frozen water molecules.

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Blog – Learn

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Discover the basic fundamentals of structural geology, the response of natural materials to deformation, and what changes occur due to the application of stress and or strain energy. Practical Geomechanics will be covering the many aspects of exploration, assessment and production phases of petroleum reservoir development.

Blog Learn

The Society of Independent Professional Earth Scientists (SIPES) would like to invite you to join us in Houston on October 24th, 2014 at the Marathon Oil Building for the SIPES Continuing Education Seminar.

Blog Learn

Looking at a formation as a source rock, then turning around and considering it a viable reservoir requires you to be able to shift your thinking and to analyze a great deal of data in a new way. If you don’t, you risk not understanding the nature of “sweet spots” and how to accurately complete or use reservoir characterization studies.

Blog Learn

Designed for geologists, geophysicits, petrophysicists and petroleum engineers this course will present the concepts of sedimentary geochemistry and biogeochemistry, along with the framework to interpret elemental and mineralogical records in such organic rich mudstone sequences

Blog Learn

Recent announcements have positioned the Springer Shale as a potentially prolific producer at 12,500 ft depth, with Continental Resource’s initial tests producing more than 2,000 barrels per day.The Springer, which is a Mississippian-Pennsylvanian boundary zone formation has been an important oil and gas producer in both southern Oklahoma and in the Anadarko Basin.

Blog Learn

Listen to Dr. Ronald Nelson as he shares his knowledge and insights on a practical approach to defining reservoir fluid and pressure related natural fracture generation and fracture property alteration in conventional and unconventional reservoirs.

Blog Learn

Want an introduction or review of the mineralogical aspects of reservoir quality evaluation? Well here's your chance, Mineralogy Aspects of Reservoir Quality Evaluation with a Focus on Clay Minerals,  will provide attendees with fundamental information needed to evaluate and assess reservoir quality of conventional and unconventional plays.

Energy Policy Blog

Energy Policy Blog
Europe, especially Central and Eastern Europe, continues to be at risk of a Russian cutback in natural gas deliveries. Washington, D.C., legislators optimistically claim that U.S. natural gas exports will reduce European dependence on Russian natural gas. A Brookings Energy Security Institute study suggests this is unlikely.
Energy Policy Blog
As the U.S. increases its production of crude oil, pressure continues to build to allow crude exports. U.S. Energy Information Administration (EIA) has been asked to study the economic impacts of potentially lifting the ban and those studies are expected to be released in the late 2014/early 2015 timeframe.
Energy Policy Blog

Arctic exploration and production is heating up: Shell plans to resume drilling in the arctic offshore Alaska in 2015, and in the spring of 2015 the U.S. is assuming the leadership of the Arctic Council, an intergovernmental forum created to address the concerns to Arctic nations and the region’s indigenous peoples. Undiscovered Arctic oil and gas resources are huge, as are producing onshore fields. There are only a few producing fields in the offshore arctic, but that number could expand with planned drilling offshore Russia and Alaska.


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10 Nov

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