Studies on Origin and Mixing Proportion and Resources Significance of the Coalbed Gases, Huainan Coalfield

Xiaojun, Zhang ¹
(1)Northwest Branch,Research Institute of Petroleum Exploration and Development,PetroChin, Lanzhou, China.

Huainan Coal is a nearly east-west axis of the complex syncline, within developed the folds and faults. There is coal layer of Permian Shanxi Formation, Lower and Upper Shihezi Formation. The total thickness of coal layer is 20~30m. 11-2 and 13-1 coal is the most stable coal layer in the region, is also main coal layer development and utilization of coal-bed methane resources in the mine. With gas coal as the major, part of the fat coal, coking coal. Vitrinite reflectance is generally 0.65 ~ 0.95%.We can see δ13C1 and δDCH4 value of coalbed gas from Pan 1 coal field, Pan 3 coal field and Zhangji coal field in table 1. theδ13C1 value overall -56.7‰~-67.9‰. Therefore, theδ13C1 value of colabed gas in this area is not match the thermal evolution of coal rocks.It clearly shows that the coalbed gas from Pan 1 coal field, Pan 3 coal field and Zhangji coal field is mostly biogenic gas produced by CO2 deoxygenation.

The original sample used for the experiment is biogenic coalbed gas (A) and thermogenic coalbed gases (B, C and D).

Three gas samples were mixed in different proportions, with biogenic gas of the A sample in the proportion of the mixing gas increases, the methane carbon isotope composition of the mixing gas gradually became lighter. And when the A sample in the proportion of the gas mixture more than 50%, the mixed gas δ13C1 value is usually less than -55 ‰.According to the mining area of Huainan Coalδ13C1 average and the results of a study to determine the mixing proportion of coalbed gases. The proportion of secondary biogenic gas in the Panji 1 coal field,Panji 3 coal field and Zhangji coal field is 72~79%,43~53% and 53~61% respectively. The coalbed of Huainan coal field was uplifted shallow, the gas loss led to greatly reduce the gas content, while secondary biogenic gases production increased coalbed gases content. The main coalbed of Huainan coal field the average gas content is generally greater than the basic 6m³/ t, in some areas even higher.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.