Discovery of Oil Reserves Through Production Geology

Stuart David Harker

Production geology, effectively integrated with other disciplines, resulted in an increase in main area Claymore reserves of 29 million standard bbl to date. From mid-1983 to mid-1987, daily oil production increased from 43,000 to 55,000 standard bbl.

The Claymore field is located in the North Sea, 110 mi northeast of Aberdeen, Scotland. It was discovered in 1974 and brought on stream in 1977. In 1978, main area Claymore peak daily production was 62,000 standard bbl. Production is from Late Jurassic sandstones in a truncated, tilted fault block on the southwest margin of the Witch Ground graben.

The Sgiath and Piper formations of the lower reservoir are overlain by the Claymore Sandstone Member of the Kimmeridge Clay Formation. The Claymore consists of up to 1,630 ft of thinly bedded, fine-grained turbidite sandstones and contained 95% of the main area Claymore original oil in place. The Claymore Sandstone Member is divided into two informal units: low gamma-ray sands and high gamma-ray sands.

Areal sweep and water injection effectiveness are evaluated by the use of well logs, flowmeter surveys, and RFT pressures. New well locations are selected only after very detailed sedimentology and structural geology appraisal. True vertical thickness logs are used for stratigraphic correlation. Together with core studies, high-resolution dipmeter is used for bed definition as well as structural interpretation. Three-dimensional seismic coverage is fully integrated with the use of many true-scale structural cross sections. The integration of all available geological, geophysical, and engineering data is crucial to the continuing success of main area Claymore reservoir management.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.