Prediction of current in-situ stress in Taiyuan-Shanxi Formations of northeastern Ordos Basin and its impact on coalbed methane development

The Taiyuan-Shanxi formations at the northeastern margin of the Ordos Basin is a key strata for coalbed methane (CBM) exploration and development, and its in-situ stress state is a key factor influencing reservoir permeability and the effectiveness of hydraulic fracturing. To reveal the current in-situ stress state of the coal reservoirs and its main controlling geological factors, and to analyze its engineering impacts on reservoir permeability and hydraulic fracturing, the main coal seams (4+5# and 8+9#) of the Taiyuan-Shanxi formations in the area were taken as the research object. Multiple methods, including injection-falloff tests, in-situ stress tests with differential strain analysis, triaxial rock mechanics experiments, and well logging interpretation, were used to study the current in-situ stress characteristics of the study area. Results indicated that the 4+5# and 8+9# coal seams in the study area were dominated by a normal faulting stress regime. In-situ stress increased significantly with burial depth, and its spatial heterogeneity was primarily controlled by lithology and rock mechanical properties. The in-situ stress values in coal seams were markedly lower than those in dense roof and floor plates, forming significant differences in horizontal principal stress in the 4+5# and 8+9# coal seams. Under the normal faulting stress regime, high-angle fractures were mostly open, which was favorable for improving coal reservoir permeability. In terms of hydraulic fracturing, it was inferred that fractures mainly propagated vertically. This study clarifies the vertical distribution pattern of current in-situ stress in coal reservoirs of the Taiyuan-Shanxi formation at the northeastern margin of the Ordos Basin and its key influence on reservoir development. Expected to provide a geomechanical basis for CBM well pattern deployment, fracturing design, and development strategy optimization in this area.