Abstract

In deep-well, high-permeability completions, effective control of loss of expensive, brine completion fluid is a major challenge. High bottomhole temperature, differential pressure, and brine acidity may limit the reliability of conventional fluid-loss control agents that are available for less severe conditions. Gel pills generally cannot control high-density brines because it is difficult to generate a stable gel pill in a high fluid-density environment, thereby complicating placement efficiency. Particulate-type systems may also be undesirable because of cleanup concerns.

This paper describes the codevelopment and field application of a nonparticulate, high-density fluid-loss control material consisting of derivatized hydroxyethylcellulose (DHEC) and an enhanced external breaker system. Development of the product was critical to the successful completion of the first-ever, three- phase, triple-stacked subsalt completion in the Gulf of Mexico (GOM). DHEC provides an effective method of controlling high-density brine loss during deep-well, high-permeability completions, with minimal formation damage. Within a certain temperature range, DHEC is stable in zinc bromide (ZnBr2) brines for extended periods. The enhanced acid breaker system allows the user to achieve rapid breaking of DHEC on demand. The paper also discusses the principles underlying the design and development of the material and the accompanying breaker system. The paper presents the laboratory data that helped us evaluate cross link times, temperature stability, break times, and regained permeability. In laboratory tests, DHEC showed potential to effectively prevent loss of 1 7.2-lb/gal ZnBr brine for up to 36 hours at 215 F. Afterward, the breaker system broke the DHEC within 30 minutes. After this cleanup procedure was applied, the test cores had retained an average of 90% of their original permeability. In actual field applications, the fluid-loss material effectively controlled 17.2-ib/gal ZnBr2 in a GOM subsalt well while the operator used fracpacks to complete three separate zones in the same well.

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