Practice and insights into volumetric fracturing in deep coal reservoirs of the Sichuan Basin: A case study of the NT1H well

Exploration and development of deep coal seams in the Sichuan Basin remain in their early stages, with no suitable volumetric fracturing technology system yet established. To address this problem, this work compares the geological and engineering characteristics of the Longtan Formation Coal 19, the Daji Block Deep Coal 8, and the Longmaxi Formation shale in southern Sichuan. Based on the 3D discrete element method, an integrated numerical fracturing model simulating fracture propagation and proppant transport was developed to optimize operational parameters. The study reveals: ① The Longtan Formation exhibits well-structured coal seams with high quality and substantial hydrocarbon potential, distributed regionally in a stable pattern. However, it displays thin interbedded distribution vertically, with intercalated gangue primarily consisting of mudstone and shale. ② The Longtan Formation coal rock exhibits static parameters similar to those of the Daji Block Deep coal 8, but with thinner continuous vertical thickness. Compared to the Longmaxi Formation shale, it possesses better porosity and permeability conditions, lower Young's modulus, higher Poisson's ratio, and more developed joints and microfractures, making overall stimulation more challenging. ③ Based on the reservoir characteristics of the deep Longtan Formation coalbeds, a distinctive volumetric fracturing concept was initially developed. Field results demonstrate that this volumetric fracturing technology enabled the NT1H well to achieve a peak daily gas production of 10.6×10⁴ m³ and a stable daily output of 8.0×10⁴ m³. These findings provide valuable guidance for fracturing operations in deep coal seams within the Sichuan Basin and serve as an important reference for similar block stimulation projects.