Relationship between Fractures, Fault Zones, Stress and Reservoir Productivity in the Suban Gas Field, Sumatra, Indonesia
It is becoming widely recognized that there is a relationship between stress, stress heterogeneity, and the permeability of subsurface fractures and faults. We present an analysis of the South Sumatra Suban gas field, developed mainly in fractured carbonate and crystalline basement, where active deformation has partitioned the reservoir into distinct structural and stress domains. These domains have differing geomechanical and structural attributes that control the permeability architecture of the field. The field is a composite of Paleogene extensional elements which have been modified by Neogene contraction to produce basement-rooted forced folds and neo-formed thrusts. Reservoir-scale faults were interpreted in detail along the western flank of the field and reveal a classic oblique-compressional geometry. Bulk reservoir performance is governed by the local stress architecture which acts on existing faults and their fracture damage zones to alter their permeability, and hence their access to distributed gas. Reservoir potential is most enhanced in areas that have large numbers of fractures with high ratios of shear to normal stress. This occurs in areas of the field that are in a strike slip stress style. Comparatively, reservoir potential is lower in areas of the field that are in a thrust fault stress style where there are fewer fractures with high shear to normal stress ratios. Achieving the highest well productivity relies on tapping into critically-stressed faults and their associated fracture damage zones. Two wellbores have been drilled based on this concept and each shows a three-fold improvement in flow potential.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California