Publications

This paper describes the impact of the present day stress state on the permeability of faults and fractures in a South Sumatra field. Under certain stress conditions, faults/fractures with suitable geometry can be under high-shear stress that can promote shear slip, dilation and enhanced permeability, such fractures/faults are called critically stressed. Identifying such faults/fractures is important for understanding the production behaviour and for field development. This paper discusses identification of stress regime through using logs and drilling data and determining the conditions that can result in critical stress state of fractures/faults. Based on the quality of available data, two representative wells were selected. Initially, borehole image interpretation was performed to pick faults, fractures, and bedding dips. The majority of the conductive fractures had strike within twenty degrees of the present day maximum horizontal stress (SHmax) direction. A smaller group of fractures had strike similar to the present day minimum horizontal stress (Shmin) direction. For the analysis, in addition to the fracture directions, determining the horizontal stress magnitudes is essential. For this purpose, geomechanical analysis of selected wells was conducted. No extended leakoff test (XLOT) or minifrac data to calibrate stresses were available. However, a new generation of broad frequency band and directional acoustic data with multiple depths of investigations was available for one well. These data were used for estimating the magnitudes of two horizontal stresses and calibrating the formation stress profile. The predominant stress regime was found to be strike-slip, with some areas, especially the harder rocks, under a reverse stress regime. The stress profile was used to determine normal and shear stresses across fracture/fault planes and the potential of shear slip. The greatest potential for critical stress was found to be in low-angle faults/fractures with the strike within thirty five degrees of Shmin, when present in rocks under the reverse stress regime. The majority of conductive fractures with strike close to SHmax direction had little potential of being critically stressed. Production data from the wells was analyzed and experiences obtained from field production were compared with the test results. Good consistency between analysis prediction and observation is found. Analysis accuracy can be improved by acquiring additional data and conducting 3D geomechanical analysis. This procedure will form a key input into any future development programs.