| With rapid development of national economy, the demand for oil and gas energe has been steadily on the increase in China, who has become the world’s second largest oil consumption countries next to United States. To be an important type of oil and gas reservoir, carbonate formation contains 48% and 28% of global oil and gas reserves respectively. In our country, there is also large proved reserve of oil and gas in the carbonate reservoirs of Ordos Basin, Sichuan Basin and Tarim Basin. Acid fracturing is one of the most important technologies for the exploitation of carbonate formation, and the non-uniform etching surface along the fracture largely affect the conductivity and yield. Due to the deficiency of present acid fracture conductivity apparatus and the lack of acidized fracture surfaces characterization method, there is no intuitive understanding towards the effects of acidized surfaces texture to fracture conductivity. To solve this problem, an acid etching physical simulation and characterization system was designed, and an evaluation for acidized fracture conductivity in complex condition was built.(1) Based on geometric similarity, motion similarity, dynamic similarity and the similarity principle of initial and boundary conditions of physical model, a research on the similarity criterion of acid etching physical simulation was conducted. The geometry and experimental parameters of the acid etching model were determined.(2) According to the determined core sample size and experimental parameters, combined with the requirements for conventional conductivity test and acid etching test, the relevant parameters of conductivity cell’s flowing region of the acid etching physical simulation were optimized by the use of Fluent. An unique bell-shaped connector for fluid import and export was created, which effectively eliminates the jet phenomenon, and the authenticity of acidized surface texture and the accuracy of conductivity test were ensured.(3) By the deformation and derication of Forchheimer equation, an analysis method for acidized fracture conductivity test data considering non-darcy effects was built, a program for data analysis was established and acid etching physical simulation test method was built.(4) By analyzing different three-dimensional optical imaging technologies, laser triangulation method was used. Besides workflow design of three-dimensional contour scanner and the selection of laser transmitter, optical lens and camera were conducted. Finally the three-dimensional contour scanning and imaging procedures was established, the surface characterization of four unique acidized texture and the conductivity variation under different closure pressure conditions were analyzed experimentally.(5) On the basis of the core sample data of four typical acidized surface texture, combined with reverse engineering and fluids mechanics knowledges, numerical simulation method for fluid flow in acid etching fracture was first created, and the flow field changes on single-fracture surface of the four typical acid etching texture were analyzed.Based on acid etching physical simulation test method, conbined with surface texture analysis and fracture-flowing numerical simulation, an evaluation mehod for acidized fracture conductivity was formed. The results show that, both the roughness and conductivity of linear and groove etching surface are greater, but the conductivity loss of linear texture is greater than that of groove texture with the increase of closure pressure; The roughness and conductivity of uniform and point etching surface are low, which is classified as unfavorable etch. Besides the acidized surface texture directely affects the flowing-field change. There is non-darcy effect on the rough fracture surface, and the greater the degree of non-uniform etch, the greater the non-darcy effect. |
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