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Experimental Investigation of Acidizing in Natural Fractured Carbonates to the Optimum Injection Condition

Sheikhi, Sobhan | 2018

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 50696 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ayatollahi, Shahabodin
  7. Abstract:
  8. In many cases, oil and gas extraction from reservoirs due to damage and permeability reduction near wellbore is lower than optimum level and reduces the flow of oil into the well. In fact, formation damage is the collapse of natural condition of reservoirs, In addition to delaying production and increasing costs, it causes early desertification of wells. Well stimulation methods are used to solve this problem and increase production. One of the most effective ways to increase the production of wells is well acidizing. In this study, the acid performance of the fractured carbonate reservoirs has been investigated. In this type of reservoirs, due to the existence of high permeable paths of the fracture, most of the stimulation fluid enters to the fracture and a lot of fluid flows into them. On the other hand, the uniform distribution of acid in different layers of the adjacent matrix of the well is also important, and therefore the issue of the diversion of acid from the fracture to the matrix is raised. The purpose of this research is evaluating the amount of diversion of stimulation fluid from the fracture to the matrix and prevention of the complete loss of acid in the fracture near the wellbore, in other words, the purpose is full zonal coverage of the target area in the acidizing and the full stimulation of the matrix and the fractures. For this purpose, a diverting mixture fluid including a polymeric fiber with visco-elastic surfactant was used in the acidic medium and its function in acid diversion was investigated in compatibility and degradability tests and then core flooding, respectively. The important point is that the diversion should be temporary and after the end of the acidizing, the diverter should be decomposed into the fractures and the full path of the fractured should be fully reversed in order to produce the hydrocarbon fluid. This method is novel and has been proposed only by some reputable companies in the world, and few samples have been used in wells. Three types of polymeric fibers were selected for evaluating the efficiency of the mentioned purpose. Type 1 polymeric fiber has not been adapted to the acidic environment at high temperatures, and was therefore abandoned from the start. The results of the degradability tests showed that type 2 fibers in the base solution began to decompose after about 4 hours, and it was necessary to boil in base solution for complete decomposition up to 6 hours. While Type 3 fibers were more suitable, they completely decomposed between 30 and 45 minutes, and completely mixed the fibers and base solution into a homogeneous solution. After complete decomposition, the solution was passed through a mesh with 100 meshes and no sediment was observed on it. The core flooding experiments into calcite and dolomite carbonate cores with a fracture (artificially) and competition of acid entry between matrix and fracture has been investigated. The minimum permeability of the fractured cores was measured in this study 500 md. A precise recording of pressure drop was not possible in fractures with a permeability of more than 8 D. Proportional to the fractured core permeability, with the presence of fibers in the fracture, fractured core permeability with fibers was obtained between 100 and 500 milliards. In core flooding experiments, the permeability contrast between the fracture and the matrix is infinite due to the very low permeability of the matrix (0.1 md) and the extremely high permeability of fracture (about a few Darcy), in core flooding experiments by increasing the permeability of the matrix to about 50 md, and the permeability of the fracture at few Darcy ,the permeability ratio of the fracture to the matrix was reduced, and the diversion of the acid from the gap into the matrix was better. Therefore, by increasing the permeability of the matrix, the diversion of the acid is more effective and the presence of wormholes is more evident
  9. Keywords:
  10. Fibers ; Viscoelastic Surfactant (VES) ; Acidizing Treatment ; Fractured Carbonate Reservoir ; Experimental Investigation ; Acid Diversion

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