Resin-Cement Blend Enhances Wellbore Integrity

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 213763, “Use of Innovative Resin-Cement Blend To Enhance Wellbore Integrity,” by Wajid Ali, Faisal A. Al-Turki, and Athman Abbas, SPE, TAQA Well Services, et al. The paper has not been peer reviewed. _ A major challenge occasionally faced during a well’s life cycle is the buildup of sustained casing pressure (SCP). Compromised cement-sheath integrity is one of the primary reasons for such a pressure buildup. Meeting this challenge requires development of an isolation material that can enhance the mechanical properties of cement. This paper presents the laboratory testing and application of a resin-cement system in a scenario where potential high-pressure influx was expected across a water-bearing formation. The resin-cement system was designed to be placed as a tail slurry to provide enhanced mechanical properties compared with a conventional slurry. Introduction The objectives of this study were to investigate the use of new systems at different densities with epoxy resin as an additive and to demonstrate value added in terms of improved mechanical properties and bonding. The resin used in this study is diglycidylether of bisphenol-F, a linear epoxy resin formed by reacting bisphenol-F with a suitable amount of epichlorohydrin and hydroxide. Amines are used as curing agents for epoxy resins. The curing mechanism is a step-growth polymerization. The curing is observed initially by an increase in viscosity and then by hardening. The final product’sproperties, in terms of compressive strength and viscosity, also are affected by the type and concentration of the amine. Aliphatic amines produce more-flexible types of epoxy resins compared with aromatic amine curing agents. Aromatic amines will produce a stronger, harder epoxy resin. Experimental Study Cement Slurry Preparation and Testing. The cement slurry was formulated and mixed with a maximum speed of 12,000 rev/min for 15 seconds and then at 4,000 rev/min for 35 seconds. To condition the cement slurry, an atmospheric consistometer was used. A viscometer was used to measure rheological properties. Thickening time tests also were conducted. Fluid-loss measurements (dynamic and static) were performed on the prepared cement slurry. Dynamic fluid loss can affect rheology and thickening time of cement slurries. Static fluid loss can result in reduction in cement slurry and allow formation fluids to enter the cement slurry. Separation of water is observed when a cement slurry is allowed to stand for a period before it sets. To determine the extent of water separation, a free water test was performed to determine the extent of water separation. The test was conducted by allowing cement slurry to stand in a 250-mL graduated cylinder for 2 hours. The cement slurry was poured into a cylindrical cell and lowered into a curing chamber. While maintaining pressures and temperatures, the cement slurry was cured up to 30 days. At the end of the curing period, the pressure and temperature were reduced to ambient conditions and the test specimens were removed from the curing chamber to be tested for mechanical properties.