Fluid Loss Pills Control Losses through Sand Control Screens without Damage or Cleanup

Abstract

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 clear 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:Reduce fluid losses to the formation from inside the sand control screen,Minimize the potential for formation or screen damage, andEliminate 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. Introduction An operator working offshore Trinidad & Tobago planned to replace the production tubing in five dry gas producers. These wells were completed as deviated 8.5-in. open hole in which a 7-in. pre-perforated liner was run. Two different types of sand screens were run inside the 7-in. liner and gravel packed with 40/60 gravel (US mesh). Increased production targets initiated the workovers in which the combination 5.5 x 4.5-in. carbon steel production tubing on five of the eight platform wells would be replaced with a combination of 7 x 5.5-in. 13-Chrome production tubing. This task also included the setting of packers above the current production packer in the wellbore. Each re-completion had a planned duration of 18 days. For several reasons, including the expected increased rate of dry gas production, it was very desirable to limit losses to the formation and to isolate the sand control section during the workover, however, only chemical means of fluid-loss control were practical. The operator was concerned about losing large amounts of completion brine to the depleted sands and even more concerned about plugging the completion with immobile solids since a remedial treatment would put the operation well past schedule for returning the wells to production and put the project over budget. To achieve these objectives, the operator, its operating partner, and the completion fluid service company considered whether it was possible to formulate a fluid-loss-control pill (FLCP) that would temporarily seal the inside surface of the premium screens with minimal matrix invasion, hold kill-weight pressure for the duration of the operation and not require any remedial treatment.

Influence of the Solid Phase's Fractional Composition on the Filtration Characteristics of the Drilling Mud

“…Ishbaev [4] studied the methods of reduction in contamination of the producing formation with mud filtrate and solid particles of drilling fluid. Dick and Heinz [5] calculated bridging agents' optimum share in the drilling fluid in order to seal the permeable areas of the reservoir [6]. In drilling muds, it is feasible to use bridging agents, which are at the same time weighting agents (bridging-weighting agents) [7][8][9][10].…”