Characteristics of present-day in-situ stress field under multi-seam condtions: Implications for coalbed mthane development

China has abundant coalbed methane (CBM) resources. The eastern Yunnan region is a famous CBM pro- duction area in the south of Yangtze River,where the Yuwang Block has abundant CBM resources with some consider- able development prospects. The present-day in-situ stress state is an important geological factor influencing the explo- ration and development of CBM resources,which indicates some practical implications for effective CBM development.However,the current study on the present-day in-situ stress state within the Yuwang Block is only the statistic analysis based on some injection / falloff well tests. The differential distribution of stresses within various types of rocks has not been revealed in the areas with multi-seam conditions. Hence,in this study,the interpretations of drilling-induced frac- tures (DIFs) and borehole breakouts ( BOs) from imaging logs were first carried out. The present-day in-situ stress orientation was determined based on the relationship between stress orientation and DIFs / BOs. Stress magnitudes in the Permian coal seams were calculated using the revised Anderson model corrected with measured stress data from the injection / falloff well tests. The results show that a dominant in-situ stress orientation with N-S-trending appears in the Yuwang Block. Stress magnitudes in coal seams generally increase with burial depth,and the magnitudes of the hori- zontal maximum principal stress (SHmax ),horizontal minimum principal stress ( Shmin ) and vertical stress ( Sv ) follow the relationship SHmax ≥Sv > Shmin ,indicating a strike-slip faulting stress regime. Under the present-day in-situ stress field,the permeability in coal seams will decrease along with the increase of effective in-situ stresses. Those cleats with the strike of about 330°-150° contribute more to the CBM development in the Yuwang Block. Hydraulic fractures may propagate vertically under the strike-slip faulting stress regime. In addition,the horizontal stress difference is relatively low (about 6 MPa),which tends to form a complex hydraulic fracture system. This study quantitatively analyzes the present-day in-situ stress state in the Yuwang Block,whose results may provide some supports in the aspect of present- day in-situ stress field for the CBM exploration and development in the Yuwang Block of eastern Yunnan region.