Study on CBM and tight sandstone gas co-mining feasibility- take the Linfen block on the eastern edge of the Ordos Basin as an example

Abstract

ABSTRACT Unconventional gas resources, including a large proportion of coal bed methane (CBM) and tight sandstone gas, are abundant in China. Presently, there is an issue of low production and high cost in single-layer mining of CBM and tight sandstone gas. Co-mining of CBM and tight sandstone gas has received extensive attention. Studies on co-mining are still in the field test stage, lack theoretical support, and require further study. Based on reservoir geologic conditions in the Linfen block, a non-channeling geological model for tight sandstone and coal seam is established using Eclipse to perform a numerical simulation of co-mining and simulate the effects of different parameters. Effects of permeability, porosity, reservoir thickness, water saturation, and Langmuir Volume on the contribution of gas production to different production layers were analyzed. A comprehensive evaluation index is established and used to judge the co-mining feasibility of 14 wells (J-1 to J-14) in the No. 8 coal seam and adjacent sandstone layers in the Linfen block. Results show that with increasing ratio of permeability, ratio of porosity, and ratio of reservoir thickness (sandstone/coal), the accumulative gas contribution rate of sandstone for 20 years increases gradually. With increasing water saturation in sandstone and increasing Langmuir Volume in the coal seam, the accumulative gas contribution rate of sandstone for 20 years gradually decreases. The Linfen block has favorable strata characteristics for co-mining, well J-1, well J-3, well J-4, well J-8, well J-9, well J-10, well J-12, and well J-13 in No. 8 coal seam are suitable for co-mining. Wells J-2, J-5, J-6, J-7, J-11, and J-14 are suitable for single mining.