Research on the influencing rule and main controlling factor coalbed methane reservoir stimulation

ABSTRACT: China's coalbed methane (CBM) development has shifted from shallow to deep (>2000m). Compared with shallow reservoir, deep coal has higher gas saturation (>60%), higher free gas content, more cleats, better diagenesis, higher formation pressure gradient; a breakthrough from 10,000 m3/day to 100,000 m3/day has been achieved through large-scale fracturing and high-intensity sand-adding. In this study, a numerical simulation model considering the cleat development, stress characteristics, and horizontal well perforation was established. Based on this, the single-factor influence law of 12 factors in 3 aspects was studied; five indexes (reservoir transformation volume, number of cleat communication, maximum hydraulic fracture length, width of transformation area, and formation deformation) were proposed to evaluate the effect of deep CBM reservoir transformation. An orthogonal test program with 48 groups (L48(410)) of 10 factors and 4 levels was designed to obtain the main controlling factors for the safe reforming and production enhancement of deep CBM. It is demonstrated that controlling factor for safety transformation is net pressure. For the production enhancement, the construction process has the greatest impact, followed by cleat properties, and finally, reservoir mechanical characteristics. To ensure the productivity and safety simultaneously, it is crucial to optimize the net pressure during construction.