Gas Production Prediction Model and Parametric Analyses for Fractured Horizontal Well in Deep Coalbed Methane Reservoirs

ABSTRACT: To ensure the long-term, efficient, and stable development of deep coalbed methane, it's urgent to conduct research on gas production prediction and influencing factors analyses. In this study, based on the three zones (stimulated zone with proppant filled, stimulated zone without proppant filled, and un-stimulated zone) distribution in deep coalbed methane reservoirs developed with fractured horizontal wells, composite pseudo-steady-state gas-water productivity equations are established. Subsequently, coupling this productivity equation with pressure propagation models considering well shut-in, dynamic permeability models, and the material balance equations, a composite gas production prediction model for fractured horizontal wells in deep coalbed methane reservoirs is proposed and solved. Finally, the validations using commercial numerical simulation software and history matching with field case are conducted, and the influencing factors on gas production in deep coalbed methane reservoirs are analyzed. Results show good agreements between the predicted and actual results are achieved for both synesthetic case and field case. The sensitive influencing factors on gas production are ranked as follows: number of fractures, free gas saturation, fracture half-length, permeability of Zone I, Zone I size, degree of coal fines blockage, permeability of Zone II, Zone II size, permeability of Zone III, and horizontal well spacing. 1. INTRODUCTION As a type of unconventional resource, coalbed methane is a very clean natural gas resource. Its development and utilization not only increase the rare low-carbon clean energy, but also serve as a practical carbon neutral industrial path, which can significantly reduce methane emissions during coal mining and reduce the greenhouse gas effect of methane. The shallow coalbed methane resources in China are 30.1 trillion cubic meters, and the preliminary estimate of deep coalbed methane resources can reach 40 trillion cubic meters. Obviously, deep coalbed methane resources are richer than those in the middle and shallow areas. Regarding the depth limit of deep coalbed methane, American scholars defined it as coalbed methane with a burial depth greater than 1,524 meters in the coal reservoir; Based on the progress of coalbed methane in recent years, Xu has proposed that deep coalbed methane specifically refers to those with a burial depth greater than 1500 meters in coal reservoirs. The industry gradually agrees that coalbed methane with a burial depth greater than 1500 meters is called deep coalbed methane.