A Hybrid Model for Selecting Horizontal Candidate Wells for Re-Fracturing of Tight Oil Reservoirs—A Case Study in the Baikouquan Formation, North Mahu Oil Field, Western China

The North Mahu Oilfield in western China contains abundant tight glutenite oil resources. The use of horizontal well fracturing has become the main development method in the region. However, the tight oil reservoirs have poor physical properties. After a period of production, some hydraulic fractures in the horizontal wells close, resulting in rapid decline in production. Therefore, Re-fracturing must be implemented to restore and increase oil production. In this paper, a comprehensive evaluation model for the horizontal well selection of tight oil re-fracturing is established, and a three - hierarchy system including the target layer, the criterion layer and the scheme layer is structured. The analytic hierarchy process (AHP) method, grey correlation (GR) method and entropy weight (EW) method are used to calculate the weights of factors influencing re-fracturing effects, and TOSIS method is combined to quantify the re-fracturing potential of the candidate wells, so that well H is selected to implement re-fracturing construction based on the established mathematical model. From the aspects of oil reserves, reservoir energy, wellbore conditions and reservoir fracability, the feasibility of re-fracturing of well H was carried out, and the degradable granular chemical diverting agent was preferentially used. The design of "re-open old fractures + perforate new holes+ supply reservoir energy+ real time microseismic monitoring" was designed. Re-fracturing construction of well H was implemented smoothly, and the obtained stimulated reservoir volume (SRV) exceeded 107m3. According to the production data, the daily oil production continued to rise initially, which was once over 30t/d.