This paper describes workover and completion operations offshore Trinidad & Tobago and the Gulf of Mexico in which the operator desired non-mechanical isolation of the reservoir section above the sand-control assembly. Each well required lear brine of kill-weight density and in the case of the five dry gas wells described, losses of significant volume of brine to the formation was unacceptable. Isolation of the reservoir was required for up to 18 days. The following objectives were specified: 1. Reduce fluid losses to the formation from inside the sand control screen, 2. Minimize the potential for formation or screen damage, and 3. Eliminate post-job, clean-up treatment of any kind. This paper describes the development of specially formulated fluid-loss control pills and their subsequent use in the field to provide reservoir isolation by placing a temporary filter cake on the inside surface of the sand control screen. The paper describes laboratory tests designed to optimize the pill formulation to seal the inside surface of each specific screen, minimize spurt loss, maintain rheological properties for an extended period at reservoir condition and, importantly, displace off the screen with gas production. In each of the cases described, field spotting procedures were designed to eliminate killing the wells by bullheading, thus significantly reducing the volume of fluid lost to the reservoir. The authors provide details of the properties of the pill and the field procedures used to place the pills in the wells. All wells were returned to production without any remedial treatment whatsoever or impact on productivity. Additionally, the savings in time, costs and lessons learned associated with these projects and recommendations for similar future projects are discussed.
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