Factors Influencing Coal Bed Methane Reservoir in Southeastern Edge of Ordos Basin, China

The Lower Permian Shanxi Formation marine-continental transitional organic-rich shale is one of the most important potential shale gas plays in the Ordos Basin, China. However, the content and origin of desorbed gas from the Shanxi Formation are poorly documented, limiting the understanding of gas generation and potential play elements. Geochemical characteristics of desorbed gas, including content and origin, are analyzed from 17 core samples of the Shanxi Formation from well SL-1. The results show that the Shanxi Formation shales in the study area are characterized by high total organic carbon content of 1.17-2.63%, type III organic matter, and high T max between 493 and 513 C. The desorbed gas content of the shale samples varies from 0.22 to 0.50 m 3 /t, with an average of 0.37 m 3 /t, and shows a positive correlation with total organic carbon. The gases are dominated by methane (69.57-89.02%), with small amounts of ethane (0.01-0.09%). The carbon isotopic signature d 13 C 1 ranges from À49.5 to À45.3%, and the d 13 C 2 ranges from À23.3 to À14.7%. In addition, gases released from the Shanxi Formation core samples are thermogenic in origin and possibly coal derived, as the Whiticar chart and the diagram of ethane versus d 13 C 2 suggest.

Section: Geological Settingmentioning

confidence: 99%

Characteristics and origin of desorption gas of the Permian Shanxi Formation shale in the Ordos Basin, China

Sun

Wang

Wei

et al. 2017

“…Coal absorption capacity determines the reserve capacity and production process of CBM (Wang et al, 2006b;Ding et al, 2012). Methane adsorption isotherm experiments on Nos.…”

Section: Absorption Capacitymentioning

confidence: 99%

Characteristics of Coalbed Methane Reservoirs in Faer Coalfield, Western Guizhou

Jiang

Lin

et al. 2013

Based on analysis of the geological background and gas content data in Faer coalfield, we discuss the occurrence characteristics of coalbed methane (CBM) and its distribution along the stratigraphic sequence and in coal seams. We analyze the methane adsorption isotherm experiments, reservoir deformations and mercury intrusion porosimetry (MIP), and further discuss the reservoir physical properties. The results show that gas content and gas content gradient of CBM fluctuate with stratigraphic sequence that is mainly caused by the difference in absorption capacity of each coal seam and distributions of CBM reservoir pressure systems. The relatively low gas content gradients of those coal seams buried below 500 m depth result from the dissipation of CBM into the surrounding rocks of thin and unstable Nos. 28 to 34 coal seams and the lateral migration of CBM along the strata in high-elevation area. The Yangmeishu syncline and topography are the main controlling factors that affect the current distribution pattern of CBM content, which is higher in the north than in the south and has a northeastern trend. The theoretical gas saturation is generally lower than 60%, combined with welldeveloped brittle fractures and macropores, formed by structural deformation. The exploration prospects for CBM in Faer coalfield is good.

“…Tectonic evolution controls coalbed methane accumulation through generation, preservation, accumulation, enrichment and late adjustment and reconstruction (Ding et al, 2012). In other words, it controls the CBM accumulation process by controlling coalbed burial history, thermal history and hydrocarbon generation history.…”

Section: Structural Control On Cbm Accumulation 21 Control Of Strucmentioning

confidence: 99%

Studies on Main Factor Coupling and Its Control on Coalbed Methane Accumulation in the Qinshui Basin

Wang

Xu²,

Jiang

et al. 2013

There are many factors controlling coalbed methane (CBM) accumulation. So, it is fundamental for CBM exploration and development to identify these factors and investigate their control mechanism. Through statistical analysis of experimental and field test data, the basin tectonic evolution, sedimentary environments and hydrodynamic conditions are comprehensively analyzed, and the gas control mechanism of three main factors (structure, sedimentation and hydrodynamic force) is discussed. Results show that the tectonic evolutions complicated the process of CBM reservoir formation. Multi-episode tectonic stress fields with different features reform the physical properties of coal seams that make areas with high structural principal stress difference convert to high permeability reservoir areas. The mudstone cap rock develops well in shallow water delta system. The coal seams are thick and distributed stably in deltaic plain swamp, and their abundant vitrinite, micropores and strong adsorption capacity are favorable for CBM accumulation. Appropriate hydrodynamic condition may carry secondary biological gas into the gas reservoir to supply gas source, and it is also the main force of methane carbon-isotope fractionation during CBM drainage and production. The methane carbon-isotope fractionation is available to identify the yield stability of CBM well.