Development and Field Application of a New Fluid-Loss Control Material
Authors: Nguyen Philip D. , Weaver Jimmie D. , Cole R. Clay , Schulze Charles R. 
Published: December 2007

Abstract
Providing effective fluid-loss control without damaging formation permeability in completion operations has been a prime requirement for an ideal fluid-loss control pill. A grated-gel material manufactured from a derivatized hydroxyethylcellulose (HEC) polymer gel exhibited excellent fluid-loss control over a wide range of conditions in most common completion fluids. This particular grated gel was compatible with formation material and caused little or no damage to original permeability. Detailed measurements of fluid loss, injection, and regained permeability were taken to determine the polymer particulate's effectiveness in controlling fluid loss and to assess its ease of removal. These measurements were taken under realistic conditions of static and dynamic flow through cores with liquid permeabilities ranging from 0.4 md to 120 darcies Gel strength of the particles controlled the extrusion pressure, and particle-concentration controlled the spurt loss of the completion fluid.
This paper describes the laboratory development and field implementation of the new fluid-loss control material. Static and dynamic fluid-loss studies are presented at a simulated overbalance pressure up to 1,000 psi. Studies demonstrating regained permeability and completion fluid compatibility are included as well as the important chemical considerations for this new material. This paper also provides field studies that demonstrate the material's effectiveness for controlling fluid loss in high-overbalanced completion operations, as well as its convenience and time savings.

Introduction
Conventional fluid-loss control pills including oil-soluble resins, carbonate, and graded salt fluid-loss additives have been used with varying degrees of fluid-loss control. These pills achieve their fluid-loss control from the presence of solvent-specific solids that rely on filter-cake buildup to inhibit flow into and through the formation. However, these additive materials can cause severe damage to near-wellbore areas after their application. This damage can significantly reduce production levels if the formation permeability is not restored to its original level.
Long periods of cleanup have been a major disadvantage of using these conventional fluid-loss additives. Fluid circulation, which in some cases may not be available, is often required to provide a high driving force, which allows diffusion to take place to help dissolve the concentrated buildup of material (such as the salt pill). Oil-soluble resins and graded salt particulate will remain isolated in the perforation tunnels unless they are in contact with solvent. However, their dissolution rate can be extremely slow even when they are surrounded with solvent.
The use of conventional gel pills such as linear viscoelastic or heavy metal-crosslinked polymers in controlling fluid loss requires pumping the material through large-diameter tubing because of high friction pressures. Experience, time, and an inflexible gelling schedule are also required in preparing the material at the wellsite.
The following criteria were used for developing the fluid-loss control system:–The system must be effective for fluid-loss control and compatible with and nondamaging to the formation.–The system must be readily dispersible in and compatible with completions fluids and versatile under extreme conditions of the well, including high pressure and temperature.–The system's fluid must be nontoxic, fast and easy to remove and cleanup with acid, and able to help retain well productivity.–The material must be ready to use without on-location preparation and allow for mixing and pumping with conventional equipment.
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