Guidelines for Breaker Selection in High Viscosity HEC Based Gel Plugs

Abstract

Operators can face multiple challenges during various completion and workover operations, one of which is fluid loss into the formation. Ensuring minimal fluid loss is of the utmost importance, particularly in highly permeable zones as expensive completion fluids are pushed into the porosity of the formations, usually resulting in perm damage.Available techniques for controlling fluid loss primarily include mechanical or chemical options. Mechanical techniques, although widely used successfully, have drawbacks, such as plug failure at high-pressure/high-temperature HP/HT conditions, requiring an additional trip. With industry needs for lower costs and better fluid-loss control (FLC) systems, many chemical systems have been developed to help overcome such problems associated with mechanical systems. These chemical systems include linear polymers, CaCO 3 ϩ polymer gel, sized salt ϩ polymer gel, and oil soluble resins. Although effective, these are either expensive or can leave residue behind as a result of incomplete break, causing formation damage. Crosslinked hydroxyethyl cellulose (CLHEC) based gel plugs can provide effective FLC and are used post-perforating in addition to before and after gravel pack operations. They consist of highly viscous, solids-free crosslinked gel, prepared in medium and low density brines. CLHEC based gel plugs form a filter cake, which can be removed by internal and/or external breakers as a means for cleanup.To obtain a desired break time, understanding the behavior of the breaker under bottomhole temperature (BHT) conditions is vital. This study focuses on investigating various internal and external breaker actions at temperatures ranging between 120 and 270°F. The laboratory data provided in this paper demonstrates the performance of various breakers, such as oxidizers, delayed-release acids, and selfdegrading particulate systems in low and medium density brines. The information provided in this study offers a guideline for an appropriate breaker selection in hydroxyethyl cellulose (HEC) based gel plugs.