Abstract: The deep coal seam reservoirs are characterized by ultra-low permeability, well-developed micropores, but poor connectivity, and
great difficulty in reservoir reconstruction. In order to deepen the understanding of reservoir stimulation mechanism of No.8+9 deep coal seams in the eastern margin of Ordos Basin and to provide guidance for the subsequent fracturing construction, a hybrid model with two-stage synergistic architecture has been proposed, and the characteristics of fracturing construction curves of No.8+9 deep coal seams and sand-coal stacked layers have systematically been analyzed, which reveals the influence mechanism of parameters such as sand addition amount, number of stages, and perforation technology on the fluctuation of construction pressure, and clarifies the production capacity of vertical and directional wells with various fracturing parameters. In addition, the targeted fracturing technology has been put forward and applied to field practice. The study results show that the “TSLANet–Kmeans++ (DTW)” hybrid model has the best performance under various classification conditions, and it has the best discrimination when classifying fracturing curve of deep coal seams into four types, i.e., pressure plateau after high pressure fracturing, steadily pressure rising, steady pressure decline, and difficult sand addition, with the accuracy of the model reaching up to 92.7%. The staged plugging technology and pre-pad fluid volume have a great influence on fracturing pressure. For wells with high rock breaking pressure peaks, multi-stage plugging, high pre-pad fluid ratio and low viscous fluid ratio can be used to reduce risks of fracturing complex caused by high fracturing pressure. The main controlling factors for well production capacity include liquid volume, sand addition amount, displacement, and sand ratio. It is beneficial for enhancing well production capacity by fracturing with less water, controlling liquid volume, increasing sand–liquid ratio, and increasing displacement. A composite fracturing and reconstruction technology for deep coal seams with the core idea of “repeatable low-damage fracturing fluid + multi-stage plugging + high displacement + temporary plugging at the fracture opening end” has been proposed and successfully been applied in wells A-18 and B-4H, with a steady single well gas rate exceeding 10×10⁴ m³/d, which provides theoretical basis and technical support for the high-efficiency development of deep CBM in Ordos Basin.

Key words: eastern margin of Ordos Basin, deep coal seam, fracturing curve pattern, controlling factors for production capacity