Physical Simulation Experiment On Superposed Gas-bearing System Production Under Different Production Schedules

Coalbed methane(CBM)is not only a clean energy,but also a greenhouse gas.The large-scale exploitation and utilization of coalb CBM is of great significance to the improvement of energy structure and the protection of ecological environment.However,due to the widespread development of superposed gas-bearing system(SGS)in China,a series of technical problems such as great differences in physical properties and fluid properties between different coal reservoirs are faced in the middle and long term of production.Therefore,taking 18#coal seam in Jinjia Coal Mine of Guizhou Province as the research object,this paper carries out physical simulation experiments of CBM production under different production schedule by using self-designed physical simulation test device of SGS,and probes into the evolution of reservoir pressure,coal temperature,coal deformation and production flow rate in different production schedule.The main results are as follows:(1)The physical simulation experiment of single-layer production of CBM in SGS is carried out by using self-developed"SGS CBM production test device".Four coal seams with different reservoir pressures are designed to form a SGS system,which realizes the independent control of gas production in a single coal seam,avoids the interlayer interference in superimposed coal seam production,and clarifies the interlayer interference in CBM production.The dynamic evolution law of reservoir parameters reveals the interlayer influence mechanism in the process of CBM exploitation.(2)On the basis of single-layer production,the physical simulation experiment of SGS for CBM commingled production was carried out.The real-time variation law of reservoir pressure,temperature,deformation and flow rate during CBM production was analyzed,and the interlayer interference phenomenon in commingled production was revealed.The results showed that CBM was poured back from high reservoir pressure to low reservoir pressure,and high reservoir pressure.The productivity contribution of coal seam is relatively large,while that of low reservoir pressure coal seam is relatively small.(3)Based on single-layer production and commingled production,physical simulation experiment of progressive production of CBM in SGS is carried out,and the gas production time of each coal seam is optimized.The analysis results show that progressive production can effectively avoid the occurrence of gas backfilling between reservoirs,reduce interlayer interference,improve the productivity contribution rate and recovery rate of low reservoir pressure coal seam,and make the productivity distribution of each coal seam relatively coincide.(4)Through quantitative analysis of parameters such as instantaneous flow q,cumulative flow Q,productivity contribution rateωand recovery rateηin the process of CBM production,the differences of production effects between single-layer production,commingled production and progressive production are compared,the characteristics of gas production of each coal seam under different production schedule are discussed,and the relatively ideal mining system(progressiveⅣ→Ⅳ+Ⅲ→Ⅳ+Ⅲ+Ⅱ→Ⅳ+Ⅲ+Ⅱ+Ⅰ).(5)The difference coefficient D is put forward,and the optimization effect of progressive production schedule is evaluated quantitatively.By dividing the difference coefficient D_i of each coal seam into three types,it is found that the difference coefficient D of superimposed coal seam is always positive,and the overall change trend shows the evolutionary law of rising first and then decreasing gradually.It shows that the progressive production schedule in SGS is the same as that in commingled production schedule.A more ideal production schedule.