Optimum Matrix Acidizing Treatment Methodology for Wells Located in The Haoud Berkaoui Field, Algeria

Abstract

Abstract The most common reason of formation damage is the drilling operations. Mud invasion is the major problem that affects well productivity in HAOUD BERKAOUI field. As the source of damage is known, different types of acid systems are proposed by service companies to improve the near wellbore formation permeability. Matrix acidizing treatment is successful and economic when either no excess volume or insufficient volume is used. The determination of acid volume is complicated and is generally based on field experience or using rules of thumb. Rules of thumb may not be convenient and always over estimate or underestimate the volume. Selection methods based on laboratory experiments, however, are more close to real estimates since they take into consideration the rock mineralogy. In this study, laboratory tests are discussed and their results are shown to determine the mineralogy and formation characteristics of HAOUD BERKAOUI field. Acidizing tests of 4 different acids are conducted and discussed to select the optimum fluids. Visual observations of cores using SEM are also used as interpretation tools. Besides, optimum volume is predicted based on the laboratory acid response curves. Laboratory test results show permeability improvement for 3 systems. However; one system proposed to treat injection wells gave mediocre results. Tests also show the risk of emulsion and/or precipitations for some acids. Acid system 3 with 6% HCl and 1.5% HF is found to be the optimal fluid to treat both injection and production wells. This system presents a good permeability improvement with less damaging precipitates and no risk of emulsion. Guidelines for acid volumes based on 6% HCl –1.5% HF acid are provided and could be used as a starting point in acidizing job design for HAOUDBERKAOUI field. Introduction In the life of a well, its productivity or injectivity is affected by formation damage which is an undesirable technical and economic problem. Formation damage can occur during the drilling or coring operations, well completion, workover and production. Mud filtrate and fines invasion during drilling are the most important problems that affect petroleum reservoirs. They affect the reservoir as pore blocking by solids, clay swelling and dispersion and liquid block which reduces effective permeability to hydrocarbons. Damage is detected in production wells by a decrease in production and by an excessive pressure build up in injection wells. Many techniques are developed to overcome formation damage and to restore or ameliorate wells productivity. One of those method is "Matrix acidizing" which consists of injecting acids into the formation below fracturing pressure to eliminate the damage around the well. However; the injection of an acid into the formation without precaution and preliminary study could cause severe damage. Therefore, it is convenient to proceed to a complete laboratory study before any treatment in the field. Recently, Haoud Berkaoui field suffers mainly from formation damage related to drilling mud. Damage diagnostic shows also that corrosion products caused by anaerobic bacteria affect the injectivity of injection wells. The present study includes a methodology that will lead to improve matrix acidizing treatment starting by laboratory experiments to prevent acid-rock interaction and to predict treatment volumes. Different laboratory tests are conducted to evaluate Haoud Berkaoui rock characteristics as well as to evaluate the interaction between 4 types of acid and the rock for optimal selection. Moreover, 7 wells are selected on the basis of productivity impairment and are proposed for matrix acidizing. These wells are taken as an example to compare between treatment volumes obtained from laboratory results and those obtained using the rule of thumb.