Off-bottom liner cementing operations in horizontal wells on Alaska's North Slope led to the development of a unique and patented crosslinked polymer/borate/salt (PBS) plug material. Functioning to temporarily plug back the horizontal wellbore while the gas isolation liner is reciprocated and rotated during cementing, the PBS plug protects the production zone from surge and swab pressures and minimizes the risk of sidetracking during cement cleanouts.

Fluid properties and the functional physical and chemical properties of the plug include: viscoelasticity and elevated low shear rate viscosity for plug-flow displacements, and thixotropy to aid plug placement; workable set time; no syneresis; combination of low fluid loss and water/acid solubility to minimize formation damage; a final plug shear strength high enough for functionality and low enough to ensure removal by washing or jetting.

This paper describes the use and field performance of the plug in the off-bottom cementing procedure, and reports pre-set fluid properties, chemical and physical properties, and mixing and spotting procedures. Information is also presented on how the plug has been used to combat difficult lost circulation problems encountered during drilling, workover, and coiled tubing operations.

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