Study On Fracture Formation Condition Of Low Permeability Coal Seam With Multiple Crack Fracturing

Conventional hydraulic fracturing technology is no longer sufficient to meet the production needs of coalbed methane.The multi-crack network fracturing technology seeks to create more and more complex fracture networks to improve the permeability of coal reservoirs and to develop oil and gas fields.It has achieved significant benefits,which has played a good guiding role in the development and utilization of coalbed methane.On the premise of summarizing the characteristics of low-permeability coal reservoirs,the formation conditions of multi-fracture fracturing networks are analyzed,and the parameters of cleats in coal and rock are statistically analyzed through geological surveys.Based on Monte Carlo stochastic theory,computers are programmed using ANSYS numerical analysis software.Language,programming of geometric parameters,construction of a two-dimensional planar natural cleat model,and numerical simulation methods were used to analyze the effects of hydraulic fracturing under different conditions.Based on the above research,the following conclusions have been obtained:When the angle between the principal stress and the surface cleat is 0°,although the expansion direction and the cleat direction of the hydraulic fracture are parallel to each other,it is not conducive to opening and communicating the closed cleat unit,and the formed reservoir has the smallest influence range;The included angle between the principal stress and the surface cleat is 10°~20°,reaching the maximum area of seepage,and the fracturing effect is good,and is consistent with the microseismic monitoring results.With the increase of the cleat density in coal and rock,the seepage area produced by hydraulic fracturing increases exponentially,and the fracturing effect increases significantly.The cleat density is the key factor to increase the reservoir permeability;with the content of cleaved minerals in coal and rock With the increase,the seepage area caused by hydraulic fracturing will be reduced and the fracturing effect will be worse.With the increase of the cleat length in coal and rock,the seepage area generated by hydraulic fracturing will increase slightly,but the cleat length will increase to a certain extent.When the degree of seepage area no longer increases,it has little effect on the fracturing effect.It can be concluded that,for a better multi-fracture network,the order of importance is cleat density> mineral fill> cleat length.The research conclusions can be used to optimize the fracturing process and high permeability zones,which provides a certain theoretical basis for the stimulation of CBM wells.