Studying the Breaking Mechanism of Polymer-Based In-Situ Gelled Acids using Solid Breaker

Abstract

In situ gelled acids that are based on polymers have been used in the field for several years as an acid diversion agent. These acids should not cause permanent formation damage, and should clean-up rapidly and completely when the well is put back on production. However, recent lab studies indicated that a significant amount of gel was retained inside the core even when the recommended breaker concentration was used. This gel significantly reduced the core permeability. Therefore, the objective of this study is to examine the working mechanisms of the solid breaker and the factors that affect the breaking time. The flowback of the spent acid and the core damage induced by it will also be assessed in detail.Viscosity and rheological experimental studies were conducted using polymerbased in situ gelled acids that used Zr as a crosslinker agent. To form the gel, this acid was neutralized using Pink Desert limestone to pH 3.5-4.The rheological properties of the gel were measured under different breaking conditions for 2 hr using HPHT when the values of elastic modulus (G') were equalized with the viscose modules (G").An HPHT filter press was used to simulate the flowback of the spent acid.Viscosity measurements of filtered fluids were used to determine the degree of gel degradation. Carbonate cores that had a 2.5 in. diameter and 0.25 in.thickness were used.Temperature ( Also, this thesis is dedicated to my advisor who has been a great source of motivation and inspiration.