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EMD-Related Articles

Explorer Emphasis Article By Louise Durham

Accurate characterization of unconventional reservoirs requires an integrated, multi-faceted approach.

Added on 01 September, 2013

Explorer Policy Watch By Edith Allison

Shale Gas Workshops Offering Diverse Views

Starting in 2012 and continuing through this fall, the National Academies (NAS) are hosting workshops to inform the public about shale gas development.

Added on 01 August, 2013

Explorer Division Column EMD By Jeremy Boak

Finding Focus for the Year's Agenda

Even with a year of preparation as president-elect, I find myself stepping into the role of Energy Minerals Division (EMD) president with some trepidation.

Added on 01 August, 2013

Explorer Director’s Corner By David Curtiss

Good Reasons Why Keystone Should be OK'd

You don’t have to spend much time around the oil and natural gas industry to understand that it is political.

Added on 01 August, 2013

Explorer Emphasis Article By David Brown

Potential, Successes Top Regional Challenges

Latin America offers some of the most promising and most perplexing exploration prospects on the planet.

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

Accommodation-based coal cycles and significant surface correlation of low-accommodation Lower Cretaceous coal seams, Lloydminster heavy oil field, Alberta, Canada: Implications for coal quality distribution

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.

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 Director’s Corner By David Curtiss

A Scenario of Hope for Natural Gas Challenges

Global demand for natural gas continues to grow and the search is on to meet that demand in both the eastern and western hemispheres.

Added on 01 July, 2013

Explorer Emphasis Article By Louise Durham

Flowback Water Provides 'Unique Messages'

A perfect combo – Hydraulic fracture stimulation with horizontal drilling is contributing to the shale play successes in the United States and around the world.

Added on 01 July, 2013

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AAPG publications are widely read by geologists, geophysicists and reservoir engineers. Are they your target audience? Then take advantage of the many advertising opportunities available in AAPG’s news and journal magazines.

Added on 13 April, 2018

wwwUpdate Blog By Grant Smith

Free Access to AAPG's Discovery Series 10 and 15 Full Data Set Tutorials

Courtesy of AAPG and AAPG Datapages, two Discovery Series data sets have been donated free of charge for use as online teaching materials. Discovery Series 10 – Sandstone Petrology: A Tutorial Petrographic Image Atlas 2nd Edition and Discovery Series 15 – Carbonate Petrology: Interactive Petrography Tutorial, both authored by Kitty Milliken, have been posted online for easy accessibility.

Added on 11 May, 2020