Simulation Of Coal Seam Stress Field And Gas Flow Field For Hydraulic Fracturing Underground

According to the underground coal seam hydraulic fracturing process of coal moisturefiltration rate caused by the increase of gas migration in the negative effects as well as theredistribution problem of gas field, seepage field, stress field. This paper analysed thehydraulic fracturing technology in different coal structure adaptability and researched thegas desorption laws under coal-water-air three-phase medium conditions to reveal theeffect of regional stress distribution characteristics of hydraulic fracturing by adoptingtheoretical analysis, numerical simulation as well as combining laboratory experiment andindustrial experiment. Discussed the double effects of hydraulic fracturing of coalbed gasmigration and production and pointed out the feasibility of using transient electromagneticmethod and tracer method to study and evaluate underground coal seam hydraulicfracturing field distribution characteristics.(1) Experimental study on the gas desorption law which is under the condition ofcoal-water-air three-phase medium shows that the higher the coal sample moisture contentis, the less the cumulative desorption quantity and the lower the desorption rate will be;values of ΔP、q、K1decrease with the increase of coal water content. It not only gives thatwater has inhibitory effect on methane desorption and migration, but also reveals thechecking indexes which are tested under the moisture-contained condition conceal the riskof coal and gas outburst.(2) Numerical simulation of single drill hydraulic fracturing showed both sides of thedrill reduced greatly. The stress was reduced to a low state in a wide range. Coal bodydisplaced beside the drilling and in the direction on of Z. The variation of drilling cuttingsvolume of field test reflected stress concentration belt transferred to the deep coal seam.Pressure relief belt length increased in front of mining working face. The variation ofdrilling cuttings volume of field test corresponded to the distribution of stress state in thenumerical simulation. The shortage of hydraulic fracturing was discovered duringnumerical simulation. Hydraulic fracturing causes a new stress concentration at the cracktip.(3) In view of the complexity of geological conditions of coal seam occurrence andheterogeneity, and in the study of hydraulic fracturing fluid break down agent flow fieldshort circuit, fracture propagation maldistribution, haplopore point stress concentrationphenomena, propose diplopore（multihole）uniformity fracturing, directional drilling dam fracturing, hydrojet assistance fracturing, beforehand waterpower slotting guidingfracturing, karat cambridge ring gutter orient fracturing five strain design to realize coalseam whole, even used to implement the coal fracturing optimization process.(4) Flow state was applied for recognizing standard Reynolds number Re and startingpressure gradient. The studies on positive effect of hydraulic fracture accelerating gasproduction by increasing permeability, as well as negative effect of increasing moisturerestraining gas migration, reflected that moisture content is not the dominant factoraffecting the starting pressure gradient, however, while permeability of coal seam increasesto certain extent, starting pressure gradient vanishes. When it comes to a high permeabilitycoal seam, increasing moisture has a limited impact on gas extraction, and hydraulicfracture accelerating gas production by increasing permeability in essence alters the flowstate of gas in coal seam. Compared to negative effect caused by fracturing fluid loss, thepositive effect resulting from fracturing controls gas production.(5) For the problem of evaluating the distribution’s characteristics of fracturing’s flowfield(including seepage capability, influence area and degree of uniformity),we build amathematical model to evaluate the fracturing’s folw field of the coal containing gas. Weconducted the survey that is the distribution’s characteristics of fracturing’s flow field bymeans of experiment and theory,which is based on TEM and tracer method. It enriches themethod of evaluating the fracturing downhole and makes great application value toimprove the quality of site construction and reduce the risk of construction.