Enzyme-Based Cleanup Fluid Effective for High-Temperature Filter-Cake Removal

Abstract

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 214628, “Enzyme-Based Cleanup Fluid for High-Temperature Filter-Cake-Removal Applications,” by Ali A. Al-Taq, SPE, Hussain A. Al-Ibrahim, SPE, and Ali A. Alsalem, SPE, Saudi Aramco, et al. The paper has not been peer reviewed. _ Enzyme-based cleanup fluids are preferred for filter-cake-removal applications, especially in horizontal wells, because of several advantages compared with conventional cleanup fluids, including low reactivity, less corrosivity, more-positive environmental impact, and, ultimately, homogeneous filter-cake-removal coverage. Most enzyme-based cleanup fluids are limited to low temperatures. In the complete paper, the authors describe extensive laboratory work conducted to evaluate an enzyme-based/in-situ generated organic acid cleanup fluid for a water-based mud at a temperature of 250°F. Experimental Work Before describing their experimental methods, the authors provide a literature review in the complete paper detailing cleanup or removal of filter-cake damage, natural cleanup, acids and oxidizers, enzymes, enzyme-breaker systems, and factors influencing performance of enzyme breakers. The drill-in fluids used to perform the high-pressure/high-temperature (HP/HT) filter press tests were laboratory and field samples. The field samples were obtained from Well A. XC-polymer, starch, and PAC-L polymers were used in the drilling-fluid formulation to control fluid loss and to increase its viscosity. Potassium hydroxide was added to adjust the pH of the drilling fluid. Potassium chloride (KCl) was used to mitigate fines migration and clay swelling. Fine and medium calcium carbonate particles were used as weighting materials. Equipment used in the experiments included HP/HT filter-press cells, see-through cells, and a pendant-drop instrument. The inductively coupled plasma (ICP) technique was used to measure the concentration of calcium in the spent acid samples. Filter-cake solids before and after the reaction took place were analyzed using X-ray diffraction (XRD) and X-ray fluorescence (XRF) techniques. The concentrations of spent acid samples were measured by acid/base titration using 0.5-M sodium hydroxide solution and phenolphthalein solution as an indicator. Iodine tests were conducted on the treated filter-cake solids to examine the presence of starch. The pH and density were measured for various solutions. Coreflood experiments were conducted on sandstone core plugs. The coreflood-test procedure is provided in the complete paper.