Study On Diversion Capacity Of Acid Fractures Based On Digitized Characterization

As an important type of oil and gas reservoir, carbonate formation contains48%oil reserves and28%gas reserves of the global 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. But most of the reservoirs belong to tight carbonate formation, which is difficult to achieve industrial production level under conventional well completion ways. Acid fracturing is one of the most important technologies for the exploitation of carbonate formation, and the non-uniform etching surface along the fracture under the formation closure stress condition largely affects the conductivity and yield. Due to the deficiency of present acid fracture conductivity apparatus and the lack of acidized fracture surface characterization method, there is no relevant understanding towards the effects of acidized surfaces texture and closed character to fracture conductivity.In view of the results of precedent researches, some related parameters of acid etching experiment was optimized based on the principle of similarity, and single-factor acid etching experiments were carried out by using the controlling variables method. An established rough fracture surface quantification system was designed to realize3D digital imaging of acid fracture surface and quantitative analysis of the degree of non-uniform etch, which help us to explore the influence of experimental parameters on the acidized fracture morphology. Then acid fracture compaction and conductivity experiments were carried out using above samples. By combing reverse engineering techniques, a three-dimensional coupled topography visualization method was set up to achieve a visual characterization of fracture morphology distribution and analysis of fracture compaction deformation features under different closure pressure. Finally, we have thoroughly studied the influence of closure pressure, acid etching pattern, fracture closure mechanism, surface parameters on fracture conductivity.Considering the limitation of acid fracture conductivity experiment, which not only need enough experiment samples and would damage them after loading pressure, but also hard to obtain the microscopic flow process and flow field distribution in the acidized fracture, and further quantitative analysis on the effect of the tortuous flow on fracture conductivity is absent. The single fracture3D solid models were reconstructed with the help of reverse engineering software. On the basis of etching fracture conductivity research results, samples with different acid etching patterns are selected to carry out numerical simulations based on finite element method, to investigate the behaviors of fluid flow through acid fractures and to reveal the high-speed non-Darcy effect impact on the acid fracture conductivity.The results have provided an guidance for revealing the relationship between acidized surfaces texture and conductivity, and new visualization research strategy and quantitative characterization method were established for acidized fracture conductivity analysis.