Browsing by Author "Alghamdi, Abdulwahab"
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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 and Theoretical Study of Surfactant-Based Acid Diverting Materials(2011-02-22) Alghamdi, AbdulwahabThe purpose of matrix stimulation in carbonate reservoirs is to bypass damaged zones and increase the effective wellbore area. This can be achieved by creating highly conductive flow channels known as wormholes. A further injection of acid will follow a wormhole path where the permeability has increased significantly, leaving substantial intervals untreated. Diverting materials such as surfactant-based acids plays an important role in mitigating this problem. In this study and for the first time, 20-inch long cores were used to conduct the acidizing experiments in two configurations, single coreflood and parallel coreflood. The major findings from performing single coreflood experiments can be summarized as follows: The acid injection rate was found to be a critical parameter in maximizing the efficiency of using surfactant-based acids as a diverting chemical, in addition to creating wormholes. The maximum apparent viscosity, which developed during viscoelastic surfactant acid injection, occurred over a narrow range of acid injection rates. Higher injection rates were not effective in enhancing the acidizing process, and the use of diverting material produced results similar to those of regular acids. The amount of calcium measured in the effluent samples suggests that, if the acid was injected below the optimum rate, it would allow the acid filtrate to extend further ahead of the wormhole; at some point, it would trigger the surfactant and form micelles. When the acid injection rate was lowered further to a value of 1.5 cm3/min, the fluid front developed in more progressive fashion and the calcium concentration was more significant, continuing to increase until wormhole breakthrough On the other hand, the parallel coreflood tests show several periods that can be identified from the shape of the flow rate distribution entering each core. The acid injection rate was confirmed as influencing the efficiency of the surfactant to divert acid. Acid diversion was noted to be most efficient at low rates (3 cm3/min). No significant diversion was noted at high initial permeability ratios, at least for the given core length. The use of surfactant-based acid was also found to be constrained by the scale of the initial permeability ratio. For permeability ratios greater than about 10, diversion was insufficient.