Abstract

Minas oil field, operated by PT Caltex Pacific Indonesia in central Sumatra, has produced more than four billion barrels of oil since production began in the early 1950's. Today, increasing production through the identification of by-passed or unswept oil reserves is a major challenge in this densely drilled, super-mature oil field. The early success of conventional infill drilling, initiated after pattern waterflood injection, has been difficult to repeat. Recognizing by-passed oil accumulations and selecting low risk drilling locations now requires a more complex interpretation of the local geology and reservoir conditions.

Most recently, an aggressive development drilling campaign produced rather unexpected results and highlighted the necessity for a comprehensive reevaluation of the reservoir. This re-evaluation has shown that the main producing reservoirs, originally thought to be regionally continuous fluvial/deltaic sands, are commonly compartmentalized or segmented into discrete, isolated geologic units. Reservoir compartmentalization is predominately a function of the complex stratigraphic and structural setting, with a less significant role played by postdepositional diagenetic processes. A detailed depositional framework has been constructed using log data from more than 1400 wells that were calibrated to lithology utilizing 20 conventional cores. Sequence stratigraphic correlations have been made for all major producing zones to better understand the intricacies of individual flow units. In addition, a very detailed structural framework has been built using a recently acquired, high-resolution, 3D seismic survey. The accurate delineation of previously undetected faults, combined with traditional fault seal analysis, plays an important part in identifying target oil in structural compartments.