Effects of in-situ stress and joint on permeability of the coal bed in Linfen block, southeastern Ordos Basin, China
Linlin Wang1,2, Bo Jiang1, Jilin Wang1, Jiyao Wang1, Zhenghui Qu1
1Ministry of Education Key Laboratory of CBM Resources and Reservoir Formation Process, School of Resources and Geosciences, China University of Mining and Technology, Xuzhou 221116, China
2Low Carbon Energy Institute (Key Laboratory of Coal-based CO2 Capture and Geological Storage of Jiangsu Province), China University of Mining and Technology, Xuzhou 221008, China
Keywords: Локальное напряжение, трещина, проницаемость, угольный пласт, бассейн Ордос, In-situ stress, joint, permeability, coal bed, Ordos Basin
Abstract
Effects of in-situ stress and joint on permeability of the coal bed depend on orientation relationships between in-situ stress and joint. In-situ stress orientations of Linfen block of southeastern Ordos Basin were determined by systematical measurements of the loess joints. In-situ stress magnitudes were calculated based on well logging and hydraulic fracturing data. Joint orientations of the No.5 coal bed and density distributions of the overlying sandstone bed were investigated. The results show that the NE-oriented maximum horizontal principal stress, approximately parallel to the predominant joint orientation of the coal bed, is favorable to the openness of the predominant joints. The minimum horizontal principal stress, with its orientation perpendicular to the predominant joint orientation, tends to induce the closure of the predominant joints. The stress state of No.5 coal bed is σv>σH>σh, which is favorable for the openness of subvertical joints and an increase in permeability. The permeability of No. 5 coal bed increases obviously with increasing effective vertical stress and effective horizontal maximum stress and decreases with increasing effective horizontal minimum stress. Besides, the permeability of No. 5 coal bed exhibits a good exponential relationship with the density of predominant joint set. Therefore, predominant joints with the orientation of 45° mainly contribute to increases in the permeability of the No. 5 coal bed in Linfen block. Multidimensional analysis show good exponential relationships among the permeability, predominant joint density, and effective stress of the No.5 coal bed.
|
