Volume fracturing and temporary blocking volume acid fracturing technology have been formed to improve stimulated reservoir volume in the Keshen gas field in China. The key factor for high yield is to make full use of the natural fractures in the reservoir. At present, the opening mechanism of natural fractures has been studied theoretically, but in combination with the temporary blocking process at the site, the indoor verification of different levels of natural fracture opening and coupling extension needs to be further strengthened.
The indoor physical experiment was carried out according to the outcrop rock sample 30cm×30cm×30cm. Three experimental schemes were designed to study the feasibility of temporarily blocking the natural fracture. The scheme is that the natural fractures are naturally closed without filling, the fracture aperture is less than 4mm, and more than 4mm.
Through the experiment, the following understandings are obtained: In the reservoir, not all fractures can open by temporarily blocking process. The fracture aperture is a very important factor. When the crack is no propped agent and naturally closed, the temporarily blocked powder forms a plug at the slit of the fracture, and the turn opens new fractures, but the opening pressure is high. In the first experiment, the maximum pump pressure was 19.11MPa, and the maximum pump pressure for the temporary blocking was as high as 39.757MPa. When the fracture aperture is less than 4mm, it is possible to temporarily turn the steering and open the new fracture. The maximum pumping pressure is 15.91MPa, and the maximum pumping pressure of the temporary plugging is as high as 27.29MPa;
According to the experiment, in the acid fracturing design, the process design and the temporary blocking material are optimized according to the grade of the reservoir fracture, which improves the design and optimizes the stimulation process.
At present, the Kuqa piedmont area in China's Tarim Oilfield is the main area of constructing a 30×108 gas zone in the oilfield (Yu Xiao, 2018) while Dabei and Keshen blocks are the main blocks in the Kuqa piedmont area. By the end of May 2019, more than 100 deep wells and ultra-deep wells had been successfully drilled in the Kuqa piedmont area, and 6 ultra-deep wells with their depths exceeding 8000 m had been drilled (Xu Haizhi, 2019). Natural fractures are well developed in the reservoirs. The thickness of stimulated layers is 100m-300m. The highest formation pressure coefficient reaches more than 2.0MPa/100m. It belongs to the ultra-deep fracture thick sandstone reservoir with high pressure and stress.