Simulation of fracture control during temporary plugging at fracture openings in deep and ultra-deep shale-gas horizontal wells

Abstract

When deep and ultra-deep shale gas well fracturing is carried out, multi-cluster fracturing can hardly realize synchronous initiation and propagation of hydraulic fractures due to the combined effects of heterogeneity of deep in-situ stress and "dense cluster" fracture arrangement, and the strong interference between fractures aggravates the unbalanced fracture propagation degree. Field practice proves that the fracture-opening temporary plugging fracturing technology can effectively control the unbalanced propagation of multiple fractures. In addition, the application effect of temporary plugging process can be improved by developing a method for simulating fracture control during fracture-opening temporary plugging fracturing of deep/ultra-deep shale-gas horizontal wells. Based on rock mechanics, elasticity mechanics, fluid mechanics and fracture propagation theory, combined with the flow distribution equation of horizontal-well multi-cluster fracturing and the plugging equation of temporary plugging balls, this paper establishes a fracture propagation model and a fracture control simulation method for the fracture-opening temporary plugging fracturing of deep/ultra-deep shale gas horizontal wells. Then, the influences of the number of temporary plugging balls and the times and timing of temporary plugging on temporary plugging control are simulated, and the influences of temporary plugging balls on fracture propagation morphology and SRV (stimulated reservoir volume) distribution are analyzed by taking Sinopec's one deep shale gas well in Dingshan-Dongxi structure of southeast Sichuan Basin as an example. And the following research results are obtained. First, fracture-opening temporary plugging can significantly promote the balanced propagation of multiple fractures, and the simulation confirms that the number of temporary plugging balls and the times and timing of temporary plugging play an important role in fracture control. Second, as the number of temporary plugging balls increase, the SRV increases firstly and then decreases, so there is an optimal number of temporary plugging balls. Third, increasing the times of temporary plugging can improve the fault tolerance rate of temporary plugging and diverting process, but it is necessary to increase the number of temporary plugging balls appropriately. Fourth, when the timing of temporary plugging is appropriate, the balanced propagation of multiple fractures is achieved and the maximum SRV is reached. In conclusion, this method is of great significance to optimizing the design of temporary plugging fracturing, improve the implementation level of field process and develop deep and ultra-deep shale gas efficiently.