Horizontal well fracturing mode of 'increasing net pressure, promoting network fracture and keeping conductivity' for the stimulation of deep shale gas reservoirs: A case study of the Dingshan area in SE Sichuan Basin

Abstract

The deep shale gas reservoirs of Upper Ordovician Wufeng–Lower Silurian Longmaxi Formation in the Dingshan area of the southeastern Sichuan Basin have a great burial depth and complicated geologic features, so the fracturing technologies that are used for medium–shallow shale gas reservoirs are not suitable for their stimulation. In this paper, ''double sweet spot'' zones of shale gas were selected by combining engineering and geological research. The horizontal well fracturing technology suitable for deep shale gas reservoir was developed. And the fracturing mode suitable for medium–shallow shale gas reservoirs was improved. In addition, the improved fracturing mode and technology were applied in 3 deep shale gas wells in the Dingshan area. And the following research results were obtained. First, the deep shale gas reservoirs in the northwest of the Dingshan area have the characteristics of ''double sweet spot'' of geology and fracturing, and the development of natural fractures and bedding fractures provides a favorable condition for the formation of complex fracture networks after fracturing. Second, a combined fracturing mode of ''pre acid + gel + slickwater + gel'' was developed for the ''double sweet spot'' zones. In this mode, high-viscosity slickwater is adopted to increase the proppant-transport ability of liquid and enhance the fracture-creating effect, the fracturing technology of ''controlling the near and extending the far'' can increase the effective stimulated reservoir volume far from the well, and the ultra-high pressure facility can increase the fracturing displacement and the net pressure in fractures. Third, after reservoir stimulation, 3 deep shale gas wells present remarkable stimulation results, and their shale gas production rate during the testing is in the range of 10.50 × 104–20.56 × 104 m3/d. In conclusion, the improved fracturing mode and technology can provide a technical method for the stimulation of deep shale gas reservoirs in the Dingshan area, as well as a support for the breakthrough of exploration and development of deep shale gas reservoirs. Keywords: Southeastern Sichuan Basin, Dingshan area, Late ordovician–early silurian, Deep shale gas, Horizontal well, Hydraulic fracturing, Controlling the near and extending the far, Ultra-high pressure fracturing