Browsing by Subject "acid"
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Item Chemical Additive Selection in Matrix Acidizing(2011-05-09) Weidner, Jason 1981-This work proposes to survey new chemical knowledge, developed since 1984, on fluid additives used in matrix stimulation treatments of carbonate and sandstone petroleum reservoirs and describes one method of organizing this new knowledge in a software program using the Visual Basic for Applications programming language. While matrix stimulation treatments have been used in the petroleum industry for over 100 years, the last major review of the technical literature addressing this process occurred in 1984. Currently though, the petroleum industry better understands formation damage; uses different and more chemical additives in matrix stimulation treatments; and understands how some additives interact with one another affecting well performance. As a result, a new and thorough review of the literature regarding chemical additive choices for matrix stimulation treatments will help practicing engineers achieve better results worldwide. Moreover, organizing this chemical knowledge in a software program using VBA allows an engineer to access the information through Microsoft's widely available spreadsheet program, Microsoft Excel.Item Development and testing of an advanced acid fracture conductivity apparatus(Texas A&M University, 2006-08-16) Zou, ChunLeiSince the oil price has been stable at a high level, operators are trying to maximize their production to get maximum return of investment. To achieve this objective, all kinds of well stimulation technologies are applied to the proper candidate wells. Acid fracturing is a standard practice to increase the production rate and to improve ultimate recovery in carbonate reservoirs. There have been successful cases in most carbonate reservoirs around the world. However acid fracture performance varied significantly with the acid fluid type, pumping schedule, formation composition, rock embedment strength, reservoir pressure, and other downhole conditions. Engineers have tried to understand the acid transportation and dissolution mechanism and, wanted to optimize each acid job design and to predict the acid treatment effect. We made an acid fracture conductivity apparatus capable of conducting acid fracturing experiments at conditions as close to the field treatment conditions as possible. With reliable laboratory experimental results, engineers will understand the acid fracturing mechanism and build a realistic model to improve the treatment design. Our lab facility is customized for its tasks. The setup and experimental procedures are optimized to make the operations feasible and the results accurate. The fracture conductivity cell is per API standard and is modified to accommodate thick rock samples. The thick rock will create a similar downhole leakoff condition when acid flows across the fracture surface. The Chem/Meter pump is able to provide a pump rate that matches field operational conditions. All necessary measurements are recorded. The experimental data are processed and interpreted with statistics methodology. Some preliminary acid fracture conductivity experiments were carried out. A few different types of fluids are used to investigate the effects of acid concentration, fluid viscosity, and emulsification. All acid fluids had 15, 30 or 60 minutes contact time with carbonate rocks. The acid leakoff velocity is controlled at velocity 0.003~0.01 ft/min to simulate the downhole condition. Most of the experiments are successful. They can be used to validate an acid fracture conductivity model.Item Evaluation of acid fracturing based on the "acid fracture number" concept(Texas A&M University, 2006-08-16) Alghamdi, AbdulwahabAcid fracturing is one of the preferred methods to stimulate wells in carbonate reservoirs. It consists of injecting an acid solution at high enough pressure to break down the formation and to propagate a two-wing crack away from the wellbore. The acid reacts with the carbonate formation and this causes the etching of the fracture surfaces. After the treatment, the created etched surfaces do not close perfectly and that leaves behind a highly conductive path for the hydrocarbons to be produced. We distinguish the issue of treatment sizing (that is the determination of the volume of acid to be injected) and the issue of creating optimum fracture dimensions given the size of the treatment. This is reasonable because the final cost of a treatment is determined mainly by the volume of acid injected and our goal should be to achieve the best performance of the treated well. The well performance depends on the created fracture dimensions and fracture conductivity and might change with time due to various reasons. This research evaluates two field cases from Saudi Aramco where acid fracturing treatment has been used to stimulate a carbonate formation. I investigated the following issues: a) how effective was the treatment to restoring the initial productivity, b) how did the productivity of the well change with time; c) what are the possible reasons for the change in performance, d) what are our options to improve acid fracture design in the future? Based on our research work both near-well liquid drop-out and fractureconductivity deterioration can impact the production in different proportion. Moreover, the fracturing model tends to overestimate the fracture conductivity in some cases as shown in SA-2. Also, the ??Acid fracture Number?? concept proves to be an effective way to evaluate the acid fracturing treatment. Several recommendations were made based on this research work as described in the last part of my thesis.Item Experimental High Velocity Acid Jetting in Limestone Carbonates(2014-04-30) Holland, ChristopherAcid jetting is a well stimulation technique that is used in carbonate reservoirs. It typically involves injecting acid down hole at high flow rates through small orifices which cause high velocities of acid to strike the borehole wall. The combination of high kinetic energy and chemical reaction of the acid removes drilling mud filter cake from the borehole wall and produces long conductive channels, called wormholes, into the formation, therefore improving well performance. Studies have shown that injecting fluid down hole at high velocities can mitigate damage to wellbore caused by drilling mud filter cake. Both water and acid have shown positive results in such cases. However, there are no laboratory results on how high velocity acid impacts the borehole wall and the formation of wormholes. The purpose of this study is to investigate how the high velocity acid affects the acidizing treatments. The experiments are conducted on 4? diameter by 16? length Indiana limestone cores with acid injected at the velocity of 106 ft/s, 150 ft/s, and 200 ft/s. The experiments are conducted with a constant pressure differential across the core. 15%wt Hydrochloric acid is injected at room temperature at various flux rates. The results show that the higher the velocity of jetted acid, the further it penetrates into the formation. The 200 ft/s acid penetrates furthest into the core, thus potentially lowering the skin factor the greatest. A large cavity is formed into the core from the high velocity acid. This large cavity creates a pathway for acid to divert into the core to create wormholes. Acid jetting cannot be directly compared with matrix acidizing because of the formation of these large cavities. The Buijse-Glasbergen model that is used to predict the formation of wormholes does not accurately match the acid jetting data due to the formation of these large cavities, so the optimum flux and pore volume to breakthrough cannot be accurately determined.