Successful Appraisal Cum Development of Shallow and Poorer Quality Gas Reservoir in Mature Field at Minimal Cost

Abstract

The Cement Packer approach has been successfully implemented in ExxonMobil Exploration & Production Malaysia Inc. (EMEPMI) to further develop minor gas reservoirs. The reservoir of interest is of relatively poor quality and has not been tested, thus making conventional development potentially not cost effective. Several viable approaches were identified and assessed to appraise and develop the reservoir. The cement packer method, which requires relatively minimal investment was then selected as being the most suitable in pursuing these behind casing opportunities. Group 1 sands in Field A are the shallowest hydrocarbon reservoirs which are relatively thin and have low porosity and permeability. The existing completions are currently producing from deeper reservoirs, with the top packer located below the Group 1 sands. Developing the opportunities behind casing in these sands using the conventional pull tubing workover approach may be cost prohibitive. The cement packer approach, where the tubing was punched to create tubing-casing communication and cement was subsequently pumped through the tubing and into the casing, was identified as one of the potential cost effective solution. The hardened cement then acts as a barrier to satisfy operating guidelines. The reservoir was then additionally perforated, flow tested and successfully monetized. Prior to well entry, tubing and casing integrity tests were performed to confirm the integrity. This step is critical to ensure that cement will only flow into the casing where the tubing was punched. Once the cement is hardened, pressure test from the tubing and from the casing indicated the cement has effectively isolated both tubulars. Subsequent Cement Bond Log and Ultrasonic Imaging Tool also displayed nearly 120m of fair to good cement above the target perforation depth. These data served as basis and proof that the cement packer was solid and the reservoir was ready for additional perforation. Taking into account the relatively poor reservoir quality, it was decided to perforate the reservoir twice with the biggest gun available to increase the probability of maximum reservoir contact while minimizing skin. Post perforation, a sharp increase in the tubing pressure was observed, indicating pressure influx from the reservoir. The casing pressure however, remained low, confirming no tubing-casing communication and thus the success of the cement packer. The well was later able to unload naturally from the high reservoir pressure. The work program also managed to confirm the producibility of the reservoirs. This successful approach has opened up potential application to similar stranded reservoirs behind casing.