Abstract:

Due to the deep buried depth（3 500~4 200 m）, high ground stress, high ground stress discrepancy（7 to 17 MPa）, low reservoir brittle（< 0.5） and the undeveloped natural fracture, the hydraulic fracture of Weirong deep shale gas face the problems of high fracturing construction pressure, narrower pressure window, low sensitive sand concentration, high fracturing difficulty. Large-scale physical model experiments show that the morphology of Weirong shale fractures are composed of main fracture and branch fracture, within low fracture complexity and forming bedding seam more easily. On the basis of geology-engineering integration, the stratigraphic segmentation and clustering are optimized in combination with geological sweet spot. Through the study of the proppant transport, the placement mode and injection timing of the three-grade particle size proppant have been optimized, which increase the sand loading. The transverse complexity of fractures is improved by the combined temporary plugging steering fracturing technology. The net pressure and complexity of fractures are improved by the temporary plugging in the fractures and the optimization of construction discharge and liquid viscosity, thereby improving the fracturing volume and control reserves. The research results have been successfully applied in Weirong Gas Field. The sand loading has been increased to 1.95 t/m, the average open flow per well is 38.5×10⁴ m³/d, and the single well EUR is 90×10⁸ m³. All those shows a significantly improvement compared with the previous stage. Post-pressure evaluation shows that the fracturing effect is positively correlated with the sand adding strength. Therefore, how to improve the sand adding strength and control the strength of the liquid used in deep shale gas is the key to economic and effective fracturing.

Key words: deep shale gas, close-cut, fracturing, intensity of sand, temporary plugging and steering, fracturing volume