A Method To Identify The Strike Slip Faults Masked By Pseudo En-Echelon Patterns: A Case Study Of Middle Indus Basin Pakistan

Middle Indus Basin of Pakistan is well established gas prone area witnessed by many producing fields. Most of the discoveries are from three way dip closure with one side bounded by strike-slip fault. The faults with spatial continuity are proven to be sealing at Lower Goru E-Sand level of Cretaceous age. Consequently, the lateral continuity of the fault gains key importance in establishing trap integrity. The challenge becomes even bigger where seismic data has poor to fair S/N ratio. It is evident on 3D data that strike-slip fault when grown upward fault evolved into en-echelon pattern. At places, where the data becomes week at E Sand Reservoir which sits at an intermediate level exhibit an apparent en-echelon pattern whereby masking the continuity of main strike-slip fault. This paper is focused to find a method to establish weather the faults which appears to be en-echelon on seismic are really en-echelon or a continuous strike slip fault with adjoining normal faults. Due to minimal vertical throw of the strike-slip faults it becomes difficult to identify these faults on weak seismic reflector, while its branching faults having relatively larger throws become prominent and appears to be in en-echelon pattern, while the main strike slip fault is masked. To resolve this issue a method adopted was to look for some strong reflectors above and below the main reservoir, and then run seismic attributes to these strong reflectors instead of the main reservoir. This method worked very well in Middle Indus basin especially in Kadanwari gas field and Gambat Exploration License where the prospectivity was hampered by apparent pseudo en-echelon fault patterns. The method identified obscured faults to be a continuous strike slip fault, and was proven by drilling results