Research On Pre-evaluation Method Of Key Parameters Of Coal Rock Segmentation Hydraulic Fracturing

Segmental hydraulic fracturing technology has a wide application prospect in coal seam permeability enhancement,but in actual construction,due to different processes and geological conditions and other factors,as well as stress interference phenomenon between fractures,segmental fracture extension has not yet achieved the expected effect,resulting in less than ideal effect of downhole coal seam permeability enhancement.In order to optimize the fracturing process in actual construction,the study on the factors affecting the expansion of segmented hydraulic fractures in coal seams is carried out,so as to provide technical support for realizing the ideal uniform fracture network,better improving the coal seam permeability,enhancing the effect of hydraulic fracture pressure relief and permeability increase,and promoting the efficient extraction of gas.This paper proposes a pre-evaluation method for the influence factors of segmental hydraulic fracture expansion,which is studied by means of theoretical analysis,numerical simulation,and field test.By constructing a numerical model of segmented hydraulic fracturing in coal seams,the effects of five factors on fracture expansion,namely injection rate,main stress difference,fracture spacing,fracture sequence,and fracture number,are investigated,and a pre-evaluation model is constructed to evaluate and analyze the simulation results,and the magnitude of the effects of each factor alone and together is investigated.The main results achieved are as follows.(1)The effects of different injection rates,horizontal stress difference and crack spacing on the extension and extension of segmental hydraulic cracks were analyzed by finite element simulation software.The results show that,under the condition of constant other factors,increasing the injection rate can help reduce the inhibition of intermediate fractures due to the stress interference phenomenon;the larger the stress difference,the less susceptible to fracture extension;the smaller fracture spacing will lead to excessive changes in induced stress,which is more likely to affect the fracture morphology and inhibit its extension;the effect of sequential fracturing on fracture extension is minimal;single fracture The extension of single fracture is easier than that of multiple fractures.(2)The results of the numerical simulation were analyzed using the evaluation model,and the degree of fracture extension was evaluated under the combined effect of single and multiple factors;although the injection rate can improve the desirability of fracture extension,there is a certain limitation range,and the degree of influence on fracture extension is: fracture spacing > stress difference > injection rate.(3)The construction plan was designed according to the characteristics of geological parameters of Cuijiagou coal mine,and the most ideal fracturing parameters were obtained by comparative analysis using the fuzzy evaluation method,and long borehole segmental fracturing was carried out in the top plate of 2305.After the construction was completed,the peak stress diagram and stress-time diagram of the borehole were analyzed in depth to obtain the stress change law under the influence of stress disturbance and injection rate,and the regional distribution law of fracture development pattern under each segmental stress was summarized;the changes of gas extraction concentration and pure volume of extraction before and after fracturing were analyzed to further judge the fracture development and gas extraction effect,which verified the accuracy and It verified the accuracy and suitability of the pre-evaluation method.