Publications

Explorer Geophysical Corner By Farrukh Qayyum,Nanne Hemstra,Paul DeGroot,Satinder Chopra

A New Approach to Stratigraphic Interpretation

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

Added on 01 September, 2013

Explorer Emphasis Article By David Brown

Canadian Crews Survey Christchurch Faults

Canadian crews survey Christchurch faults, receive enthusiastic support from local governmental agencies.

Added on 01 September, 2013

Learn! Blog By Susan Nash

China's Shale Plays: Subject of Research Conference

China is vigorously promoting shale production, which creates excellent opportunities for joint ventures, consulting, and knowledge exchange.

Added on 21 August, 2013

Explorer Regions and Sections By Carol McGowen,Michael McWalter

Countries' Teamwork Brings Survey Success

I have just returned from Kompong Thom town, the capital of Kompong Thom Province, some 200 kilometers north of Phnom Penh, the capital of Cambodia.

Added on 01 August, 2013

Bulletin Article

Variable gas content, saturation, and accumulation characteristics of Weibei coalbed methane pilot-production field in the southeastern Ordos Basin, China

Using diverse geologic and geophysical data from recent exploration and development, and experimental results of analysis of gas content, gas capacity, and gas composition, this article discusses how geologic, structural, and hydrological factors determine the heterogeneous distribution of gas in the Weibei coalbed methane (CBM) field. The coal rank of the Pennsylvanian no. 5 coal seam is mainly low-volatile bituminous and semianthracite. The total gas content is 2.69 to 16.15 m3/t (95.00–570.33 scf/t), and gas saturation is 26.0% to 93.2%. Burial coalification followed by tectonically driven hydrothermal activity controls not only thermal maturity, but also the quality and quantity of thermogenic gas generated from the coal. Gas composition indicates that the CBM is dry and of dominantly thermogenic origin. The thermogenic gases have been altered by fractionation that may be related to subsurface water movement in the southern part of the study area. Three gas accumulation models are identified: (1) gas diffusion and long-distance migration of thermogenic gases to no-flow boundaries for sorption and minor conventional trapping, (2) hydrodynamic trapping of gas in structural lows, and (3) gas loss by hydrodynamic flushing. The first two models are applicable for the formation of two CBM enrichment areas in blocks B3 and B4, whereas the last model explains extremely low gas content and gas saturation in block B5. The variable gas content, saturation, and accumulation characteristics are mainly controlled by these gas accumulation models.

Added on 31 July, 2013

Bulletin Article

Mechanisms of shale gas storage: Implications for shale gas exploration in China

This article reviews the mechanisms of shale gas storage and discusses the major risks or uncertainties for shale gas exploration in China. At a given temperature and pressure, the gas sorption capacities of organic-rich shales are primarily controlled by the organic matter richness but may be significantly influenced by the type and maturity of the organic matter, mineral composition (especially clay content), moisture content, pore volume and structure, resulting in different ratios of gas sorption capacity (GSC) to total organic carbon content for different shales. In laboratory experiments, the GSC of organic-rich shales increases with increasing pressure and decreases with increasing temperature. Under geologic conditions (assuming hydrostatic pressure gradient and constant thermal gradient), the GSC increases initially with depth due to the predominating effect of pressure, passes through a maximum, and then decreases because of the influence of increasing temperature at greater depth. This pattern of variation is quite similar to that observed for coals and is of great significance for understanding the changes in GSC of organic-rich shales over geologic time as a function of burial history. At an elevated temperature and pressure and with the presence of moisture, the gas sorption capacities of organic-rich shales are quite low. As a result, adsorption alone cannot protect sufficient gas for high-maturity organic-rich shales to be commercial gas reservoirs. Two models are proposed to predict the variation of GSC and total gas content over geologic time as a function of burial history. High contents of free gas in organic-rich shales can be preserved in relatively closed systems. Loss of free gas during postgeneration uplift and erosion may result in undersaturation (the total gas contents lower than the sorption capacity) and is the major risk for gas exploration in marine organic-rich shales in China.

Added on 31 July, 2013

Explorer Spotlight On…

Utah Team Wins IBA

Geoscience students from the University of Utah took the top prize in this year’s AAPG/AAPG Foundation Imperial Barrel Award competition, beating out 10 other teams from geoscience departments from around the world.

Added on 01 July, 2013

Bulletin Article

A hierarchical approach to architectural classification in marginal-marine systems: Bridging the gap between sedimentology and sequence stratigraphy

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.

Added on 30 June, 2013

Explorer Article By Kimberley Corwin

Hydrates' Gas Potential Leaps Toward Reality

Japan has taken a leap forward in natural gas production by conducting the first successful production test of natural gas from marine hydrates. Could this be the“bridge” fuel needed in the coming energy transition?

Added on 01 June, 2013

Bulletin Article

Three-dimensional paleomorphologic reconstruction and turbidite distribution prediction revealing a Pleistocene confined basin system in the northeast Nankai Trough area

Integrated three-dimensional (3-D) paleomorphologic and sedimentary modeling was used to predict the basin architecture and depositional pattern of Pleistocene forearc basin turbidites in a gas hydrate field along the northeast Nankai Trough, off central Japan. Structural unfolding and stratigraphic decompaction of the targeted stratigraphic unit resulted in successful modeling of the paleobathymetry at the time of deposition. This paleobathymetry was characterized by a simple U-shaped paleominibasin. Subsequent turbidity current modeling on the reconstructed paleobathymetric surface demonstrated morphologically controlled turbidity current behavior and selective turbidite sand distribution within the minibasin, which strongly suggests the development of a confined turbidite system. Among three candidate inflow patterns, a northeasterly inflow pattern was determined as most likely. In this scenario, flow reflection and deflection caused ponding and a concentration of sandy turbidite accumulation in the basin center, which facilitated filling of the minibasin. Such a sedimentary character is undetected by seismic data in the studied gas hydrate reservoir formation because of hydrate-cementation–induced seismic anomalies. Our model suggests that 3-D horizon surfaces mapped from 3-D seismic data along with well-log data can be used to predict paleobasin characteristics and depositional processes in deep-water turbidite systems even if seismic profiles cannot be determined because of the presence of gas hydrates.

Added on 30 April, 2013

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