Genesis of Coalbed Methane and Its Storage and Seepage Space in Baode Block, Eastern Ordos Basin

Abstract

The Baode block on the eastern margin of the Ordos Basin is a key area for the development of low-rank coalbed methane (CBM) in China. In order to find out the genesis of CBM and its storage and seepage space in Baode block, the isotopic testing of gas samples was carried out to reveal the origin of CH4 and CO2, as well, mercury intrusion porosimetry, low temperature nitrogen adsorption, and X-ray CT tests were performed to characterize the pores and fractures in No. 4 + 5 and No. 8 + 9 coal seams. The results showed that the average volume fraction of CH4, N2, and CO2 is 88.31%, 4.73%, and 6.36%, respectively. No. 4 + 5 and No. 8 + 9 coal seams both have biogenic gas and thermogenic methane. Meanwhile, No. 4 + 5 and No. 8 + 9 coal seams both contain CO2 generated by coal pyrolysis, which belongs to organic genetic gas, while shallow CO2 is greatly affected by the action of microorganisms and belongs to biogenic gas. The average proportion of micropores, transition pores, mesopores, and macropores is 56.61%, 28.22%, 5.10%, and 10.07%, respectively. Samples collected from No. 4 + 5 coal seams have developed more sorption pores. Meanwhile, samples collected from No. 8 + 9 coal seams exhibited a relatively low degree of hysteresis (Hg retention), suggesting good pore connectivity and relatively high seepage ability, which is conducive to gas migration. The connected porosity of coal samples varies greatly, mainly depending on the relative mineral content and the proportion of connected pores.

Hydrogeochemical Disparities and Constraints of Water Produced from Various Coal Seams in the Baode Block, Ordos Basin, China

“…The western part of the block has gently dipping strata with angles of 3 to 7°, while the eastern part has relatively steeper dips of 5 to 10°, with some small-scale faults present locally (Figure 1d). 32 The coal-bearing formations in the area primarily consist of the Shanxi and Taiyuan Formations (Figure 1c). The Shanxi Formation is characterized by fluvial and deltaic facies, with coalbearing deposits ranging from 30 to 116 m in thickness.…”

“…The main structure of the Baode block is relatively simple, generally exhibiting a prominent monocline with a significant northwestward dip. The western part of the block has gently dipping strata with angles of 3 to 7°, while the eastern part has relatively steeper dips of 5 to 10°, with some small-scale faults present locally (Figure d) …”

“…8 + 9 coal seams are located in the lower and middle sections of the P 1 s and the P 1 t, respectively, and they are well-developed and stable throughout the block. The maximum reflectance of vitrinite in the coal seams is between 0.79% and 1.15%, indicating middle- and low-rank coal …”

Numerical-Well-Testing Interpretation of Injection/Falloff Testing for Coalbed Methane Well in Hedong Coalfield

“…The method we employed will not only help us understand the testing fluid flow in CBM reservoirs but also be able to improve the interpretation accuracy during IFOT. It will be very conducive to the exploration and extraction of CBM [16]. It will also help to reduce the danger of methane explosion or aerologic risks and obtain greater reliability for safe mining [14].…”

Pore Fractal Characteristics of Different Macro-Coal Components and Influence on Adsorption/Desorption: A Case Study in the Huanglong Jurassic Coalfield

“…Coalbed methane (CBM) is an essential clean energy and an influential supplement of national oil and gas resources and has received widespread attention around the world. − Coal seams are naturally fractured reservoirs composed of matrix blocks. The pore structure is complex and the gas is mainly absorbed in micropores. − The different macro-coal components and material composition have an obvious influence on the pore type and pore connectivity of coal reservoir as well as the enrichment and exploitation of coalbed methane. − At present, advanced laboratory techniques, such as scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), low-temperature adsorption isotherm, and mercury porosimetry, are mainly used to study pore structure characteristics. − However, it is difficult to accurately and quantitatively characterize the heterogeneity of coal reservoirs by conventional methods, and fractal theory provides a different idea for quantitative characterization of the complex pore structure of coal reservoirs.…”