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Coalbed Methane

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AAPG offers two short courses in conjunction with this year’s Unconventional Resources Technology Conference (URTeC). A wealth of information in a short period of time, theses short courses are an effective and efficient way to learn about the industry.

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This year, URTeC has added an enhanced preview of “Coming Attractions.” In addition to looking at established plays, URTeC will provide significant information about emerging unconventional resource possibilities in North America and around the world.
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The influence of moisture, temperature, coal rank, and differential enthalpy on the methane (CH4) and carbon dioxide (CO2) sorption capacity of coals of different rank has been investigated by using high-pressure sorption isotherms at 303, 318, and 333 K (CH4) and 318, 333, and 348 K (CO2), respectively. The variation of sorption capacity was studied as a function of burial depth of coal seams using the corresponding Langmuir parameters in combination with a geothermal gradient of 0.03 K/m and a normal hydrostatic pressure gradient. Taking the gas content corresponding to 100% gas saturation at maximum burial depth as a reference value, the theoretical CH4 saturation after the uplift of the coal seam was computed as a function of depth. According to these calculations, the change in sorption capacity caused by changing pressure, temperature conditions during uplift will lead consistently to high saturation values. Therefore, the commonly observed undersaturation of coal seams is most likely related to dismigration (losses into adjacent formations and atmosphere). Finally, we attempt to identify sweet spots for CO2-enhanced coalbed methane (CO2-ECBM) production. The CO2-ECBM is expected to become less effective with increasing depth because the CO2-to-CH4 sorption capacity ratio decreases with increasing temperature and pressure. Furthermore, CO2-ECBM efficiency will decrease with increasing maturity because of the highest sorption capacity ratio and affinity difference between CO2 and CH4 for low mature coals.

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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.

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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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Regional variations in thickness and facies of clastic sediments are controlled by geographic location within a foreland basin. Preservation of facies is dependent on the original accommodation space available during deposition and ultimately by tectonic modification of the foreland in its postthrusting stages. The preservation of facies within the foreland basin and during the modification stage affects the kinds of hydrocarbon reservoirs that are present.

This is the case for the Cretaceous Mowry Shale and Frontier Formation and equivalent strata in the Rocky Mountain region of Colorado, Utah, and Wyoming. Biostratigraphically constrained isopach maps of three intervals within these formations provide a control on eustatic variations in sea level, which allow depositional patterns across dip and along strike to be interpreted in terms of relationship to thrust progression and depositional topography.

The most highly subsiding parts of the Rocky Mountain foreland basin, near the fold and thrust belt to the west, typically contain a low number of coarse-grained sandstone channels but limited sandstone reservoirs. However, where subsidence is greater than sediment supply, the foredeep contains stacked deltaic sandstones, coal, and preserved transgressive marine shales in mainly conformable successions. The main exploration play in this area is currently coalbed gas, but the enhanced coal thickness combined with a Mowry marine shale source rock indicates that a low-permeability, basin-centered play may exist somewhere along strike in a deep part of the basin.

In the slower subsiding parts of the foreland basin, marginal marine and fluvial sandstones are amalgamated and compartmentalized by unconformities, providing conditions for the development of stratigraphic and combination traps, especially in areas of repeated reactivation. Areas of medium accommodation in the most distal parts of the foreland contain isolated marginal marine shoreface and deltaic sandstones that were deposited at or near sea level lowstand and were reworked landward by ravinement and longshore currents by storms creating stratigraphic or combination traps enclosed with marine shale seals.

Paleogeographic reconstructions are used to show exploration fairways of the different play types present in the Laramide-modified, Cretaceous foreland basin. Existing oil and gas fields from these plays show a relatively consistent volume of hydrocarbons, which results from the partitioning of facies within the different parts of the foreland basin.

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It’s all about staying on target: Technological advances are helping to make geosteering an increasingly valuable tool for geologists involved in horizontal wells.

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Recount: The U.S. Geological Survey offers a new estimate of the world’s undiscovered conventional oil and gas resources.

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In-Person Training
Golden Colorado United States 04 June, 2015 06 June, 2015 14707 Desktop /Portals/0/PackFlashItemImages/WebReady/ace2015-ft-12-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Coalbed Methane, Oil Shale, Oil Sands, Shale Gas, Tight Gas Sands, Engineering, Reservoir Characterization, Field Trips, Conventions, Post-Convention
Golden, Colorado, United States
4-6 June 2015
This three-day field trip will examine examples of tight-oil reservoirs (Cretaceous Niobrara Formation, Codell member of Carlile Formation from the Denver and North Park basins), tight-gas reservoirs (Cretaceous J Sandstone, Codell and Williams Fork Sandstone, from both the Denver and Piceance basins), CBM reservoirs (Cretaceous Cameo Coals from the Piceance Basin) and potential oil shale resources (Green River Formation of the Piceance Basin).
San Antonio Texas United States 18 July, 2015 18 July, 2015 14514 Desktop /Portals/0/PackFlashItemImages/WebReady/sc-Geomechanics-For-Completion-Optimization-In-Unconventionals-hero.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Structure, Geomechanics and Fracture Analysis, Oil Sands, Oil Shale, Shale Gas, Tight Gas Sands, Coalbed Methane, Production, Engineering, Hydraulic Fracturing, Development and Operations
San Antonio, Texas, United States
18 July 2015

Geomechanics – in both completions and drilling operations – has become a critical technology in the development of Unconventional Plays. This course presents the basics of oil field geomechanics and its application to unconventional developments; specifically, the role of stress, pore pressure, mechanical properties, and natural fractures on hydraulic fracturing operations.

San Antonio Texas United States 18 July, 2015 19 July, 2015 13769 Desktop /Portals/0/PackFlashItemImages/WebReady/hero-assessment-forecasting-and-decision-making-in-unconventional-resource-plays.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true Business and Economics, Oil Sands, Oil Shale, Shale Gas, Tight Gas Sands, Coalbed Methane, Risk Analysis
San Antonio, Texas, United States
18-19 July 2015
This course is oriented towards the recognition and characterization of uncertainty in unconventional reservoirs. Starting with resource/reservoir assessment methods, it moves through the full unconventional value-chain. This two-day exercise and example filled workshop provides participants with the techniques and reasoning needed to validly assess the merits of the search for, and development of, unconventional resource plays.
Online Training
29 October, 2009 29 October, 2009 1445 Desktop /Portals/0/PackFlashItemImages/WebReady/oc-es-application-of-thermal-maturation.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true
29 October 2009

Expanded package for CEU credit is $100 for AAPG members, and $145 for non-members. Special Student Pricing: $25 for Webinar only; $35 for Expanded package.

01 January, 2013 01 January, 9999 1473 Desktop /Portals/0/PackFlashItemImages/WebReady/oc-cc-unconventional-resources.jpg?width=100&height=100&mode=crop&anchor=middlecenter&quality=75amp;encoder=freeimage&progressive=true
1 January 2013 - 1 January 9999

Unconventional Resources is an online course that enables participants to learn about shale gas, shale oil and coalbed methane.

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