Production Strategy for Gas Cap-Oil Rim-Water Drive Reservoirs: A Case Study of the N Field, Mehsana Asset, India

Abstract This technical paper presents a production approach implemented in the N field, where a reservoir characterized by a gas cap, oil rim, and water drive posed unique challenges for efficient recovery. Typically, conventional reservoirs employ perforation in the oil zone to facilitate pressure maintenance through gas cap expansion and the water drive mechanism. However, in the case of the N field, production from gas cap resulted in movement of oil in the gas zone. Instead of traditional perforation techniques, the reservoir was produced through targeted extraction of the gas cap. This approach outlines the operational procedures employed, highlighting the significant oil production rates after substantial gas extraction and movement of oil in the gas zone with the geological interpretations. There are three layers in this area, K-I, K-II and K-III. K-III is majorly oil bearing while K-II has a thick oil rim and K-I has thin oil rim and major gas cap area. The well wise execution strategy of K-III, II and I have been explained in the paper. This production strategy led to reservoir management via chemical water-shut off jobs, production logging-based perforation optimization and liquid rate optimization. Following this unconventional step, the oil migrated to the anticlinal top structure of the reservoir, enabling subsequent production of oil after production of gas cap gas and till now it has yielded recovery rates of greater than 40% with current oil production of 860 tpd. The findings of this study emphasize the importance of considering unconventional production strategies tailored to specific reservoir characteristics. The case of the N field demonstrates the potential for achieving improved recovery rates and optimizing the utilization of available resources in gas cap-oil rim-water drive reservoirs. The insights gained from this unconventional approach can contribute to the development of future production techniques in similar reservoir types, ultimately enhancing oil recovery and overall field performance.