Abstract:
The low single-well production is a major challenge restricting the economic development of Coalbed Methane (CBM) reservoirs in China. To address this, considering the characteristics of organic matter in coal and pyrite are easy to be oxidative dissolved, a concept based on “net material removal-matter reduction and permeability enhancement” is proposed. This concept utilizes the oxidation effect of strong oxidants to transform solid-phase dissolution into a multi-scale mass transfer space. The technical idea of oxidative dissolution of coal on permeability and production enhancement technology for CBM reservoirs is presented, along with a workflow for the technical idea. The paper also analyzes the potential of this technical idea to enhance recovery of CBM reservoirs. The results indicate that considering the selective dissolution effect of oxidation solution on coal, the dissolution pore fracture was formed based on the induced fracture formed by hydraulic fracturing, and the fractures are extended to form the oxidative dissolution coordinated hydraulic fracturing fracture system with high conductivity. This helps resolve the three major issues currently facing CBM development engineering, achieving the goal of economically development of CBM wells. The best application conditions for this technical idea are CBM reservoirs with more than 60% vitrinite volume fraction, ultra-low water saturation, and a storage ratio of less than 0.57 for low-efficiency wells. The overall strategy for the combined oxidative dissolution and hydraulic fracturing construction scheme is “first create fractures, then dissolve, and finally increase production.” The principle of hydraulic fracturing synergistic with oxidative dissolution has been formulated: Hydraulic fracturing should be done first to create fractures; Oxidative dissolution and pore/fracture propagation; Properly controlling the shut-in time to promote fracture network communication; Reasonable drainage gas to stable production. The evaluation results of the potential for enhanced production of CBM wells through oxidation treatment indicated that treated CBM well entered the peak gas production earlier, enhancing the production of CBM well, which further verified the possibility of realizing the technical idea of oxidation treatment on permeability enhancement of CBM reservoir. A methodological framework for oxidation treatment aimed at permeability enhancement in CBM reservoirs is established, providing an important reference for the efficient development and utilization of CBM reservoirs.