Analysis On Influence Factors Of Multilayer CBM Commingled Well Productivity With Interlayer Fracturing

The coalbed methane(CBM)reserves in eastern Yunnan and western Guizhou account for about 10% of China's total CBM reserves.Because of its natural resource advantages,the development and utilization of CBM resources in the region have received increasing attention from the country.With the characteristics of thin single layer and low permeability,it is difficult to obtain ideal economic benefits by conventional development methods.To overcome the problems of low single-well production and short production stabilization time,multi-layer co-production development mode is adopted for the development of CBM in this region.To weaken the low permeability of the original reservoir and limit the production capacity of CBM wells,reservoir reconstruction has become the key.Generally,the object of reservoir reform is coal seam,but few scholars have studied the way to reconstruct the inter-layer.Due to the small spacing of coal reservoirs in eastern Yunnan and western Guizhou,two sets of coal seams can be directly connected through inter-layer reconstruction,which is more efficient than a single-layer coal reservoir reconstruction.To explore the influence of inter-layer fractures on the productivity of CBM wells,the following research work was carried out:(1)Based on theoretical analysis,considering the two conditions before and after the pressure is transmitted to the coal seam roof,a channeling model of fluid between the coal seam and the fracturing interlayer is established,and the influence law of coal seam physical properties and fracture characteristic parameters on channeling flow rate is analyzed.The channeling increases with the increase of the reservoir permeability,reservoir pressure,and fracture conductivity,and decreases with the increase of ratio of horizontal and vertical permeability.The sensitivity of each factor is ranked as follows:ratio of horizontal and vertical permeability > reservoir pressure> horizontal permeability Rate> fracture conductivity;(2)Comprehensively considering the two conditions before and after the pressure is transmitted to the coal seam roof,the two-dimensional unit model of coal seam-fracturing interlayer stacking is established using Comsol numerical simulation software,which verifies the correctness of the interlayer cross-flow model after interlayer lamination of multiple coal bed gas wells;On this basis,a three-dimensional reservoir model of coal seam-fracturing interlayer stacking is established,and a calculation method of pressure relief radius after interlayer being fractured is proposed;(3)Based on the full-process flow model for combined production of multiple coalbed methane reservoirs,the change of coal-bed fluid production channels after sandwich fracturing and its influence on the pressure relief radius are considered,and a full-process coupled flow model of multiple coal-bed gas wells with interlayer fractured is established.The productivity of multi-bed coal gas wells after interlayer being fractured is predicted,and the influence of coal seam physical properties and fracture characteristics on the production capacity of multi-bed coal gas wells after interlayer being fractured is analyzed.By comparing the gas production of interlayer fracture and non-fracturing,it is found that the productivity of co-production wells is significantly improved after interlayer fracture.