Influencing Factors of Acid Etching Fracture Conductivity of Tuff Reservoir in Northeastern Sichuan Block

Abstract

With the continuous depth breakthrough of two ultra-deep exploration wells in northeastern Sichuan block, tuff reservoir was finally discovered at the depth of 6700-7300 m. It belongs to ultra-deep tight gas reservoir with low brittle mineral content and high clay content. Hydraulic fracturing is hard to be reformed this special reservoir, easy to appear hydration expansion and other problems. However, the research and development of such tight tuff reservoir with high temperature and high pressure are relatively low in the domestic and overseas until now. Therefore, it is of great significance to carry out experimental research on relevant reservoir reconstruction methods of such rocks and explore the factors of fracture conductivity here. In this study, the influence of acid type, sanding concentrations, proppant size was research by a new experimental installation. The factors of fracture conductivity are analyzed by experimental data and the reconstitution of fracture surface. The results show that before the abnormal point, the acid etching effect of crosslinked acid on tuff is better than that of gelling acid. At the condition of closure pressure is lower 30 MPa, the higher sanding concentrations, the higher fracture conductivity, then narrowed the gap among them. Meanwhile, the larger proppant size, the higher fracture conductivity in low closure pressure. With increasing closure pressure, fracture conductivity of smaller size proppant decreased slowly. In conclusion, it is also convenient for the field operation to choose the best acid and proppant parameters. 1. INTRODUCTION As an important new field of exploration and development of oil and gas resources in the world, igneous reservoir have gradually received extensive attention from geological and petroleum researchers all over the world. The exploration and research on the igneous reservoir has a history of more than 130 years. Now, some igneous reservoir have been exploited in the United States, Indonesia, Japan, Brazil, Australia and other countries (Tang, et al. 2020). Its oil and gas mainly come from athrogenic rock reservoir. Athrogenic rock is a transitional type between magmatic rocks and sedimentary rocks, and it is also one of the important reservoir rock types. It has the advantages of thick pay information and large reserves (Li, et al. 2015). The tuff reservoir is very complex and special and has both lithologic characteristics in terms of petrophysics and diagenesis (ZHANG, et al. 2012). The low degree of development of original porosity and poor connectivity of pore throats indicate that such reservoir is tight reservoir (Zeng, et al. 2021). At present, the well known athrogenic rock reservoir in the world including East Anatolia Basin in Turkey (Gecer-Buyukutku, et al. 2005), Bohai Bay in China (Zhao, et al. 1996), Erlian (Guo, et al. 2013) and Hailar (Yu, et al. 2013) basins.