Geological adaptability analysis of PE screen pipes for coalbed methane(CBM) well completion

The collapse-proneness of coal beds in horizontal sections of a CBM well is one of the main inhibiting factors for CBM production enhancement.In view of the safety of following coal mining operation,metal pipes are not allowed to run under the coal beds.As a result,PE screen completion is an important solution to the above problem.In order to determine whether PE screen pipes are applicable or not to the coal beds susceptible to collapse,the wellbore instability mechanism of coal beds was analyzed by means of fracture mechanics,and the stress intensity factors at the fracture end of the coal rocks close to wellbore was discussed based on time delay effect,a method was further developed to judge the crack extension range in the presence of pore pressure drop funnel.The greatest potential compression force exerted on PE screen by collapsed coal rocks was investigated by example calculation.The uniaxial compressor was used in the laboratory to simulate the deformation of PE screen(outer diameter: 50.8 mm;wall thickness: 4.6 mm) caused by the falling of large coal rock blocks.The compression resistance and compression rupture judgment criteria of PE screen were determined in the test.Based on the test results,the simulation software was applied to analyze the compression resistance of screens with diameters of 50.8,63.5,76.2,88.9,and 101.6 mm respectively.Finally,the optimal wall thickness of different-sized PE screen pipes was determined,which gives certain instructions to the development and application of PE screen pipes in CBM well completion.