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Abstract: Reservoir Characterization Helping to Sustain Oil Production in Thailand's Sirikit Field

Chris E. Schaafsma, Somhan Phuthithammakul

Sirikit field is located in the Phitsanulok basin of Thailand's north-central plains. The main reservoir sequence is some 400 m thick and comprises thin interbedded fluvio-lacustrine clay and sandstones.

Initial oil volumes after exploration and appraisal drilling in 1981-1984 were estimated at some 180 million bbl. However, further development/appraisal drilling and the following up of new opportunities allowed a better delineation of the reservoirs, resulting in an increased STOIIP and recovery. Total in-place oil volumes were increased to 791 million bbl and the expectation of ultimate recovery to 133 million bbl. To date, 131 wells have been drilled, 65 MMstb have been produced, and production stands at 23,000 bbl/day.

Extensive reservoir studies were among the techniques and methods used to assess whether water injection would be a viable further development option. A reservoir geological model was set up through (1) core studies, (2) a detailed sand correlation, and (3) reservoir quality mapping. This model showed that despite considerable heterogeneity most sands are continuous. Reservoir simulation indicated that water injection is viable in the north-central part of the field and that it will increase the Sirikit field reserves by 12 million; this is now part of Thai Shell's reserves portfolio. Injection will start in 1994.

New up-to-date seismic and mapping techniques (still) using the old 3-D seismic data acquired in 1983, are being used for further reservoir delineation. This work is expected to result in a further reserve increase.

AAPG Search and Discovery Article #90982©1994 AAPG International Conference and Exhibition, Kuala Lumpur, Malaysia, August 21-24, 1994