Influence Of Multilayer Coupled Seepage Field On High-Efficiency Mining Of Coal-Fired "Three Gas"

The current world energy pattern is undergoing dramatic evolution,and China's energy is in the process of transition from solid,liquid to gaseous.The development and utilization of coal-based gas plays an important role in this pattern transformation.The application of hydraulic fracturing technology to transform low-permeability coal-series gas reservoirs is an effective means to increase production in unconventional oil and gas exploration.At present,the theory of coupling seepage and pressure crack geometric parameters calculation under coal-fired multi-layer co-production conditions has not yet formed a systematic theory.This paper relies on the Henan Provincial Natural Science Foundation project "Theoretical and technical research of " green development " of coal-bearing strata gas in Henan province"(No.182300410149),systematically study the coupled seepage and its geometric parameters under multi-layer mining conditions,the main results are as follows:(1)Based on the mining area data and the literature research results,this paper established the comparison method of the mining theory of two research areas: one is to study the comparison method of the regional pressure crack geometric parameter calculation model,and the other is to study the comparison method of the regional pressure crack multi-layer coupled seepage model.In the process of establishing the target research area model,the system can be identified according to this step,so that the model can be accurately established.(2)Based on the analysis of the influence of damage on the reservoir,this paper combined the damage factor considering the influence of damage micro-crack angle with the cracking pressure model,and the pressure crack extension pressure expansion model was derived.At the same time,based on the analysis of the nonlinear pressure drop law of the net pressure in the coal-based gas reservoir,the extended pressure expansion model and the classical PKN basic fracture analysis model were combined to establish the calculation model for multi-layer coupled seepage field crack parameters of coal-based gas considering damage effects.And the model can provide key geometric size geometric parameters for the multi-layer coupled seepage region capacity calculation model.(3)Based on the theory of analyzing the fluid mass conservation equation of reservoir unit body,combined with the three spatial regions with different seepage characteristics divided in the elliptical seepage zone,the hydropower comparison method and the equivalent seepage resistance method were used to derive the total productivity model of coal-fired vertical wells under the action of multi-layer coupled seepage field,by considering the functional relationship between the reservoir fracture crack geometry.Based on the initial parameters,the sensitivity analysis of the model's influence parameters was carried out to provide theoretical basis for bottom-hole flow pressure and half-length regulation of cracks.