Recently Added in Journals

Bulletin Article

7969
 

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.

7968
 

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.

7966
 

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.

7965
 

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.

7963
 
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.
7962
 
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

7959
 

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

7961
 

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

5780
 
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.
5779
 

 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

10760
 
Explorer Article
I have some thoughts on Lee Krystinik’s President’s Column “Bursting Bubbles” (May EXPLORER), which dealt with women, leadership and AAPG.
10761
 
Explorer Article

If you're a geoscientist who has not yet formally applied for licensure to practice your trade in Louisiana, don't despair. The registration deadline has moved - once again.

Explorer Director’s Corner

10743
 
Volunteerism is at the heart of AAPG and permeates our organization. It includes those who volunteer to help us advance science by giving a talk or writing a journal article, those who work on committees to build specific programs or services, and those who serve in leadership and governance roles.

Explorer Division Column DPA

10745
 
During my term as DPA president this year our theme will be “Culture of Greatness.” This may sound arrogant, but I think it is important to recognize and promote the culture of professionalism and discovery that has provided cheap energy for mankind for more than 100 years.

Explorer Foundation Update

10771
 
Explorer Foundation Update
The AAPG Foundation is rock solid, thanks largely to a special group of contributors known as the AAPG Foundation’s Trustee Associates. Since 1978, this group of geoscience professionals has supported the Foundation’s educational, charitable and scientific initiatives that bolster many fields of geoscience – while at the same time enjoying a special, one-of-a-kind camaraderie.

Explorer Geophysical Corner

10751
 
Risk analysis is a crucial task in making drilling decisions and involves many factors, such as well logs, modeling results, production maps and interpretation quality. In his book on 3-D seismic interpretation, AAPG award-winning member Alistair Brown presents a workflow for the quantification of interpretation confidence.

Explorer Historical Highlight

10758
 
Once we’ve completed a study most of us geologists feel that despite the incomplete data with which we started, our insight has overcome that basic limitation. Ours, however, is not an exact science– and the all-too-frequent dry wildcats return us to the level of fallible mortals.

Explorer Policy Watch

10748
 
U.S. energy production, especially oil and natural gas from shale, is booming and expected to continue to grow. Consequently, this bounty is pushing up energy exports – including coal that is displaced by natural gas in power generation – and refined products that are not regulated.

Explorer President’s Column

10729
 
AAPG must be able to nimbly and efficiently anticipate as well as respond to this changing landscape, so that we are poised to take advantage of new opportunities that arise and discard outdated strategies, technologies, products and services.

Explorer Regions and Sections

10772
 
Preparation for the FIFA World Cup was not the only event attracting international audiences to Brazil in May. AAPG’s Geosciences Technology Workshop (GTW) Brasil, "Stratigraphic Traps and Play Concepts in Deep Water Settings," brought in 143 geoscientists representing 12 countries from the Americas, Europe and Asia.
Recently Added Special Publications

Book

10484
 

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.

10482
10481
10480
8359
 

The volume highlights developments in our understanding of the palaeogeographical, palaeobiological, palaeoclimatic and cryospheric evolution of Antarctica. It focuses on the sedimentary record from the Devonian to the Quaternary Period. It features tectonic evolution and stratigraphy, as well as processes taking place adjacent to, beneath and beyond the ice-sheet margin, including the continental shelf.

8358
 

This volume provides an overview of current research on fossil and modern dinoflagellates, as well as highlighting research areas for future collaboration, following the DINO9 International Conference in Liverpool. The volume is organized into four themes, with a review paper for each theme written by the key-note speaker. Each theme also includes a future research foci note following discussion during the conference.

8357
 

This publication will be of particular interest to micropalaeontologists, other Earth scientists, historians of science, museum curators and the general reader with an interest in science.

8373
4090

CD DVD

10483
 

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.

Recently Added

GIS UDRIL Subscription Content Database Atlase

10151

GIS Open File

10137
 

Courtesy of  Dr. Ricardo J. Padilla y Sánchez for allowing the GIS project of the Tectonic Map of Mexico 2013, to be posted as a GIS Open file. This compilation shows key geologic information about Mexico.

10136
 

Courtesy of DArthur Grantz, Robert A. Scott, Sergey S. Drachev, T. E. Moore and Zenon C. Valin for allowing the Map Showing the Sedimentary Successions of the Arctic Region  that may be Prospective for Hydrocarbons, to be posted as a GIS Open file.  This map displays all of the supra-continental and submarine sedimentary successions in the Arctic Region that are known or inferred to lie at or near the land surface or the seafloor on the basis of currently available data.

10135
 

Courtesy of Janet Pitman and the United States Geological Survey for allowing the Reservoirs and Petroleum Systems of the Gulf Coast map, to be posted as a GIS Open file. This product contains GIS layer files of maps, figures, and data for the Gulf Coast Region and is recommended for independent petroleum geologists and others interested in exploration in the Gulf Coast. Using ESRI ArcReader software, the user has the ability to view and download multiple data files at different scales.

10134
 

Courtesy of Lauri A. Burke and the USGS for allowing the Distribution of Regional Pressure in the Onshore and Offshore Gulf of Mexico Basin, USA project, to be posted as a GIS Open file. The U.S. Geological Survey (USGS) has created a comprehensive geopressure-gradient model of the regional pressure system spanning the onshore and offshore portions of the Gulf of Mexico, USA.

Wiki Article

10923
 

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.

10789
 

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.

10698
 

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

10747
 

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.

10657
 

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.

Recently Added

Blog – Learn

11057
 
Blog Learn

Participants will examine illustrative outcrops of thrusts, fault-related folds, stratal architectures and facies of depositional systems affected by growing structures, which are good analogues for hydrocarbon reservoirs. Objectives include interpreting complex thrust structures, identifying and understanding strain and fracture systems in fold-thrust belts, and analyzing patterns of growth strata in areas with synsedimentary folding.

10985
 
Blog Learn

Get a first-hand look at the global nature of oil sand resources, a better understanding of advances in recovery processes, and what contributions resource geoscientists can make to the challenges of environmental protection and social license as well as driving prosperity and better standards of living for all through sustainable energy development.

Blog – wwwUpdate

10687
 
Blog wwwUpdate

See the winners, watch the videos!

8114
 
Blog wwwUpdate

There is a difference in the voting process this year. You'll want to do your research before you access the voting site.

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