ABSTRACT – The Duri Oil Field, located in the Riau Province of Central Sumatra, contains an estimated 7 billion barrels of oil OOIP. However, the oil type is “heavy”, and only 7.5% of the oil in place can be recovered by primary producing methods. Beginning in 1085, PT Caltex Pacific Indonesia began injecting steam to heat the reservoir, which is expected to yield a recovery of closer to 60% of the oil in place. The Dalam reservoir lies below the Pertama I Kedua reservoirs, and is not presently affected by the steam flood. To prolong the life of the field, and to help meet the production objective, a geological evaluation of the Dalam sandstone was undertaken. The objective of this evaluation was to identify where the Dalam is productive, oil in place and to determine if the Dalam is a candidate for steam-flooding. The early Miocene Dalam reservoir was deposited in a lower delta plain environment consisting of mud flats and tidal channels. Dalam sands are very fine to coarse grained and are thinly laminated with shale. Consequently, the Dalam is very heterogeneous. The Dalam study provides a description of reservoir heterogeneities which will effect fluid flow and steam-flooding. A successful) EOR program such as steam flooding is not only dependent on the amount of reserves, but also on reservoir heterogeneity. The geological character of the Dalam reservoir must be considered in reservoir modelling and production forecasting and in plans for tertiary recovery. Evaluation of wireline logs and core data indicate constraints to steam flooding the Dalam sandstone. Geological factors which will effect tertiary recovery are: 1) stratigraphic pinch-outs of lenticular Dalam sands, 2) faults, 3) calcite-cemented sandstones, 4) potential clay reactivity to steam, resulting in porosity reduction, 5) multiple oil/water contacts, and 6) separate, local gas caps. Despite these constraints, the Dalam is a good candidate for steam-flooding with approximately 60 to 80 million potential barrels (STB) of oil in place.
Authors : J.E. Laing & B.P Atmodipurwo