Objective In China, the Ordos Basin boasts abundant coal-measure gas resources, holding considerable potential for resource development. As the development deepens, the proportion of depleted, stripper, and inefficient wells for tight-sand gas in coal measures has gradually decreased year by year. The collaborative production of tight-sand gas and deep coalbed methane (CBM) has emerged as a significant approach to effectively releasing production capacity.
Methods To achieve the reconstruction of old wellbores and commingled production of new and old layers, this study proposed a technology of chemical temporary plugging-based full-bore reconstruction of old wellbores of tight-sand gas combined with the large-scale production of deep CBM. Specifically, a chemical temporary plugging material system was developed based on the concept of dynamic chemical temporary plugging through large-particle bridging, medium-particle filling, and adaptive powder plugging. In combination with the fractal theory and the plugging layer instability criterion, this study constructed a multi-purpose calculation model for the permeability and strength of plugging layers. Accordingly, it proposed an optimized ratio of particle sizes 3‒4 mm, 1‒2 mm, and 0.15 mm at 1:2:4 to plug low-productivity and inefficient old layers. This created favorable conditions for the fracturing and stimulation of deep coal seams. The proposed technology was applied to the field test conducted in the Linxing-Shenfu Block in the Ordos Basin, validating the rationality and feasibility of the proposed wellbore reconstruction technology and composite temporary plugging material system.
Results and Conclusions Field implementation of the optimized composite temporary plugging agent achieved full-bore wellbore reconstruction based on chemical temporary plugging, effectively plugging the stimulated reservoirs in the old well, with the pressure born by the plugging layer exceeding 60 MPa. The fracturing process using smooth casings, integrated variable-viscosity slickwater, and temporary plugging knots was employed to stimulate the deep coal seams. The pressure was maintained stable in the proppant injection stage, with no leakage sites or fracturing liquid division observed. Therefore, large-scale volume fracturing of the deep coal seams lying below the tight-sand gas layer was successfully achieved. The results of this study are expected to provide technical support for both the succeeding production of tight-sand gas pay zones in old wells and the collaborative production of tight-sand gas and CBM.
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