Publications

Production rates from wells at Mobil Oil Indonesia' Pase A field development along the Mountain Front of the North Sumatra Basin are controlled by tectonically induced fractures in a tight limestone reservoir. DST flow rates up to 30 MMCFPD have been recorded from reservoirs with 5 to 10% porosity where fractures exist, whereas wells in the same reservoir without fractures do not flow. Very tight zones, between fractured areas, have been documented by pressure and liquid/gas composition differences where no apparent reservoir discontinuities or faults exist.An interpretation of the well and seismic data, map view structures, and the regional tectonics explains the well, pressure, and flow rate data and predicts where the best fracture permeability will be located. The area appears to have had transpressive deformation associated with the oblique plate collision nearby. Prediction of fracture locations by model will depend on the relative strengths of the compressive and the strike slip components and which model is more applicable. Fractures in a compressive area will be concentrated on the anticlinally bent areas of the folds and will be perpendicular to the direction of maximum compressive stress. Fractures in a strike slip area will be concentrated as swanns near the master faults and in 60o offset features.Examination of the performance of wells that are predicted to be fractured or not by these two models, analysis of the section and map view of the deformation, and understanding the tectonic history of the area, show that there is much support for a dominantly compressional tectonic model and only little evidence for strike slip deformation after the reservoir was deposited. The evidence includes fractured anticlines, tight synclines, compressional fold geometry perpendicular to the principle compressive stress (parallel to mountain front), and lack of long straight strike slip faults, and associated 60o en-echelon deformation or pullapart and compressional areas at fault bends. The model is being tested by three extended offset production wells.