Energy & Fuels, Vol.31, No.7, 6812-6824, 2017
Cleat Orientation from Ground Mapping and Image Log Studies for In Situ Stress Analysis: Coal Bed Methane Exploration in South Karanpura Coalfield, India
Conventional well logs from three wells in South Karanpura coalfield are analyzed to correlate 10 major coal seams belonging to the Barakar formation for coalbed methane (CBM) exploration. Face cleat orientations are studied for the Simana and Argada coal seams from the Sirka and Argada mines. It varies from 130 to 140 degrees N for a total 349 face cleats observed from Simana and Argada coal seams. Cleat identification and its orientation have also been analyzed from simultaneous acoustic and resistivity (STAR) log from two CBM wells located 20-22 km away from the Sirka and Argada mines. Total number of fractures is found to be 1118 from two wells. Face cleats are not distinguishable from STAR image. Fracture density in coal is varying from 2.48 fractures per meter to 23.8 fractures per meter with a maximum density in the Banasgarah seam. Fracture orientations observed in Saunda, Sayal, Balkudra, Kurse, Hathidari, Banasgarah, and Argada vary from 10 degrees N to 115 degrees N. The in situ maximum horizontal stress (S-H) is computed from azimuthal anisotropy data, using a cross-multipole array acoustic (XMAC) log from a well. Azimuthal anisotropy ranges between 3.5% and 7.6%. The S-H orientation varies from 110 degrees N to 115 degrees N. It is observed from the XMAC azimuthal anisotropy analysis that the orientation of S-H in the Argada seams varies from 110 degrees N to 113 degrees N. The 163 face cleats in Argada seams at Argada are oriented toward 135 degrees N-140 degrees N. This indicates that the face cleats are aligned parallel to subparallel with the S-H direction. Good fracture density, open fractures/face cleats toward S-H are to be useful for CBM extraction from these wells.