High-efficiency fracturing technology and practice of high-rank coalbed methane horizontal wells in Qinshui Basin

Qinshui Basin is the main production base of high-rank CBM in China, and its annual production accounts for 60% of the national CBM production. High-rank coal reservoirs have poor physical properties and low permeability, which require fracturing to achieve effective seepage production. Horizontal well fracturing has become the main development method of high-rank CBM fields. In order to further enhance the reconstruction effect of high-rank coal reservoirs in Qinshui Basin, upgrade the fracturing technology of horizontal wells, and improve the stable gas production and EUR of a single well, based on the characteristics of high-rank coal reservoirs in Qinshui Basin, the engineering geological factors affecting the fracturing reconstruction were analyzed, and the optimization was carried out from six aspects, including fracturing interval spacing, perforation mode, fracturing fluid system, proppant combination, construction displacement and fracturing construction process. The results show that the coal in Qinshui Basin has strong plasticity and is difficult to be fractured, so higher displacement is required to produce effective fracture network; The lower the horizontal stress contrast, the more complex fracture networks tend to form, which increases the difficulty of hydraulic fracturing. The larger the horizontal stress difference coefficient is, the longer the hydraulic fracturing is, and the fractures are easy to extend; Focused energy directional perforation can gather the jet energy of the hole, avoid the near well fracture complexity caused by cluster interference, and improve the penetration depth of the main fracture and the effective reconstruction volume of the far well fracture; The composite fracturing fluid system of active water+low damage variable viscosity fracturing fluid can wet the coal seam surface while making fractures to form a protective layer. The low-damage variable-viscosity fluid system reduces friction pressure during pumping and enhances proppant transport efficiency through controlled viscosity changes, thereby meeting the requirements of reservoir protection, volume fracturing, and effective proppant placement. The multi-stage combined sand adding mode of “silt front+fine and medium sand staged support+self suspended proppant assisted sand carrying” can achieve effective support of fractures at all levels; According to the crushing index of coal from low to high, the high-rank coal in Qinshui Basin is divided into three overall evaluation intervals, in which the easy stimulation area (crushing index<6) is easy to open, and the low displacement (about 7 m³/min) stimulation can obtain high yield; The stimulative area (crushing index 7−13) needs to meet the reasonable discharge demand (about 7−15 m³/min) in order to obtain high yield; In the difficult stimulation area (crushing index ≥14), it is necessary to reach a higher discharge capacity (above 15 m³/min) to obtain high yield; The multi-stage variable displacement construction method of “multi steps and small steps” is adopted in the preflush stage. By balancing the relationship between main joints and branch joints, a pressure controlled fracture making mode of initial low net pressure (5 MPa) and later high net pressure (>10 MPa) is formed, which reduces the compaction of reservoir near the well, controls the height of joints without breaking through the top and bottom plates, and constructs a volumetric fracture network. The large-scale application of high-rank coal reservoir fracturing technology with the core of “energy accumulation directional large displacement, step-by-step fracture forming, fine sand combination, and well group synchronous interference operation” in Qinshui Basin has increased the fracture length of horizontal well pressure by 73%, the fracture network volume by 216%, and doubled the daily output of a single well, realizing the efficient development of high-rank CBM fields in Qinshui, and has been popularized and applied to high-rank CBM blocks in China, providing technical support and referential demonstration for the expansion and strengthening of the CBM industry.