The first large project area under steamflood at Duri field, Area 1, has recently been ramped down to the maintenance steam injection rate. After 14 years of steaming, Area 1 has achieved a recovery factor of about 64%. The available generated steam for this area, aside from the maintenance steam, is now being used to initiate new area development.
In 1996, the first 3D seismic survey in this area was acquired in the Southwest portion of Area 1 covering 33 patterns. This 3D seismic survey was aimed as a pilot project to identify the potential bypassed oil. The presence of the steam in the reservoir has changed the seismic velocity, distorted the seismic energy and lowered the frequency content. These factors have therefore lowered the seismic resolution to be able to resolve every injected flow unit. Vertical seismic profiles (VSP) have been heavily utilized as control data to interpret the flow unit boundaries and the faults. As a result, two major flow units (Pertama and Kedua-Baji Jaga units) were interpreted with confidence. Seismic attributes were extracted from these flow units. Pore fluid characterization was done using multi-variate statistical technique from the extracted seismic attributes to obtain the most reasonable steam saturation and bypassed oil maps which match the engineering data and production history. It was found that the bypassed oil regions were mostly controlled by both the stratigraphic and faulting systems.
A re-development strategy was generated by a multi functional team to recover the remaining oil. Seismic data was used to guide the interpretation of bypassed oil in areas not immediately adjacent to observation wells. This strategy consists of:
Selective zone re-injection
Pattern re-alignment including well conversion and infill injectors
Infill vertical and horizontal producer wells.
A target of about 4.6 MMBO of bypassed oil was identified in the study area. The approach used in this study has potential application in other areas in the Duri field that are in the earlier stages of the steamflood process. This would enable to recover of the oil as early as possible in the potential bypassed regions.