Successful Exploitation Strategy from a Mature Oil Field, in North Cambay Basin, India: A Case Study

Debashis Chakravorty
ONGC, Jorhat, India

Oil exploitation in a mature oil field comprises a great amount of investment and involves a large number of parameters related to Geological modeling, Reservoir simulation and production optimization. An oil Field in the Western margin in Ahmedabad-Mehsana tectonic block of North Cambay Basin, India, is on production since 1977. It is a multi layered structural cum stratigraphic sand stone reservoir with strong aquifer support. The main producing sand K-A has produced about 44% of its OIIP.

Oil production had started in 1977 and touched its peak in 1992. From 1992 onwards, production had started declining gradually. In order to arrest declining oil production and maximize recovery, a systematic and integrated production exploitation strategy has been formulated.

Exploitation strategy included, Geological modeling, reservoir simulation, analysis of inflow performance, gas lift optimization, preparation of 3-D dynamic water encroachment trend and successful infill drilling.

Bypassed oil was mapped based on RST logs. Well completion design of selected producers was altered and new locations were placed to drain the bypassed oil.

As 85% of total oil producers are on gas lift, an integrated modeling was made; treating the dynamic oil reservoirs, wells on lift, gas injection as a combined system and selected wells were optimized and existing GLV was redesigned.

Being a multilayered reservoir, layer wise production, pressure, water cut and structural level was analyzed and additional pay sands were opened in producing wells resulting in enhancement of oil production.
Through a variety of field examples, this paper has demonstrated 5-10% enhancement in production from a mature field with improved overall field economics and extended the life of the wells.

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