Simulation On The Fracture Propagation Laws Of Multi-stage Blasting Fracturing

Currently,there are more researches on fracture propagation by detonation gas driving,but researches on the whole process of multi-stage blasting fracturing is insufficient which is hard to provide reference for agent adding parameters at all levels of multi-stage blasting fracturing and complete theoretical supports for multi-stage blasting fracturing.Based on above researches,this article divides the whole process into two phases--first class agent blasting effects and following-up detonation gas effects—to study fracture propagation law of multi-stage blasting fracturing according to the features of multi-stage blasting fracturing.Rock impact cracking experiments were conducted on three kinds of rock samples with different brittle,the effects of first class agent explosive on the rocks impact cracking conditions were analyzed and dynamic rock breakdown pressure calculation formula were carried out through regression fitting.According to the experiment results,fuzzy comprehensive evaluation and grey relational analysis were used to build the impact dynamic load fracture number prediction model under the influence of the peak pressure,loading rate,brittleness,tensile strength and reservoir stress.Considering rock strained condition and rate dependence,theoretical calculation model of rock initial damaged area under first class agent explosive were established to analyze the relationship between initial damaged areas and impact loading rate,rock brittleness and wellbore radius.The loading rate of first class blasting should be 70¹20 MPa·ms^-1 to guarantee multi-fractures and less crushed zone.On the basis of the existing detonation gas driving fracture propagation model,considering the influence of the multi-fractures,detonation gas driving fracture propagation model was established,which was made up of fracture initiation opening displacement controlling model,blasting fracture initiation propagating criterion and fracture propagating rate.Based on a certain hypothesis,detonation gas flowing model in fracture was established using continuum equation of detonation gas flowing in fracture,momentum conservation equation and fixed pressure distribution function of detonation gas in blasting fracture.The detonation gas driving fracture propagation model was solved coupling with detonation gas flowing model and a quantitative simulation system which could be used to simulate the sensibility of fracture propagation influence under five elements including reservoir stress,rock fracturing toughness,the first class blasting load characteristics,loading rate to following-up detonation gas driving fracture propagation was developed.The results show some rules as follows:reservoir stress is positively correlated with fracture initiation and arrest pressure and negatively correlated with valid duration of detonation gas pressure and blasting fracture length;the effect of rock fracturing toughness on blasting fracture propagating could be neglected.The fracture number produced from first class agent explosive is positively correlated with fracture initiation and arrest pressure and negatively correlated with valid duration of detonation gas pressure,single explosive fracture length and overall length.The initial fracture length produced from first class agent explosive is positively correlated with valid duration of detonation gas pressure and negatively correlated with fracture initiation and arrest pressure,and has little influence on relative fracture propagating length.Detonation gas loading rate barely has any influence on fracture initiation and arrest pressure and is negatively correlated with valid duration of detonation gas pressure and fracture length.All above could provide reference and guidance on parameters design of multi-stage blasting fracturing construction.