Improving Compatibility of Drilling Fluid, Completion Fluid, and Other Well-Treatment Fluids for Deepwater Wells

Abstract

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 141513, ’Chemical Additives for Improving Compatibility of Drilling Fluid, Completion Fluid, and Other Well-Treatment Fluids for Deepwater Wells,’ by Xiaoping (Victoria) Qiu, SPE, Lee Morgenthaler, SPE, Eddy Martch, SPE, Hiep Vu, SPE, Mootasem Chtay, and Vanessa Farrell David, Shell International E&P, prepared for the 2011 SPE International Symposium on Oilfield Chemistry, The Woodlands, Texas, 11-13 April. The paper has not been peer reviewed. In Gulf of Mexico (GOM) deepwater completions, synthetic-based mud (SBM) has been used widely for drilling the reservoir section. With increasing well depth and higher reservoir pressure, higher-density drilling fluids are used. It has been observed that with the increased density of drilling fluid, the incompatibility of drilling fluid, completion fluid, and other well-treatment fluids can cause additional problems in drilling and completion activities. Often, the formation damage caused by such incompatibility can be very difficult to remediate. Chemical additives were studied for preventing this incompatibility between drilling fluid, completion fluid, and other well-treatment fluids. Introduction In deep water, wellbore cleanup is critical for drilling and completing wells. There have been cases in the GOM in which several extra days were needed to achieve acceptable cleanup. Also, when displacement is not effective, mud residue may cause formation damage in the subsequent well completion. One displacement problem is that when completion brine or spacer fluid is mixed with SBM, the mixture may form very viscous, paste-like materials that are difficult to displace or can cause problems with shaker operations. In addition to mud displacement, the compatibility of SBM and injected fluids during frac-pack operations is important. Sometimes, loss of whole mud into the formation is unavoidable when drilling and completing a well at overbalanced conditions. The mixture of SBM and completion brine lost into the reservoir may become viscous and difficult to break and flow back. Injected frac-pack fluid or gravel-pack fluid also might contact the mud and form mixtures that are difficult to move and can reduce well productivity. In GOM well-completion operations, acids are sometimes pumped before the frac pack or gravel pack to clean up the post-perforation pill and to help clean up the perforations to improve fluid injectivity. Incompatibility of SBM and acids can affect well productivity significantly. Also, HCl, organic acids, and mud acids (such as HCl/HF or organic-acid/HF acid blends) may be pumped to clean up perforations or near-wellbore damage before the frac-pack fluid is injected. If mud remains in the wellbore or if SBM is lost to the reservoir, acid may come into contact with the SBM, resulting in the viscous paste-like mixture that is worse than the mixture of SBM and brine or SBM and spacer fluid.