The Study On The Mechanism Of Multiple Fractures In Hydraulic Fracturing

Hydraulic fracturing is a widely used stimulation technique in petroleum industry for enhanced hydrocarbon recovery from low permeable reservoirs. From 1980' of the last century,along with the development of petroleum industry and the requirement to stimulate reservoirs which is more complicated,more and more people have realized that the theory of single and planar fracture can't give satisfying explain over some complex phenomena and parameter in numerous field setting.Many direct and indirect diagnostic technologies have shown the simultaneous growth of multiple-hydraulic fractures which is the main causation of the emergence premature screen-outs with low proppant concentration and the failure in hydraulic fracturing treatments.So it is urgent to analysis the forming mechanism of multiple-hydraulic fractures and the theory of simultaneous propagation of multiple hydraulic fractures ,to understand the advantages and disadvantages and the extremely high net fracturing pressures,the extend configuration of every fracture ,the mechanism of premature screen-outs,so can we offer theoretic suggestion to minimize the simultaneous propagation of multiple hydraulic fractures to give successful stimulation on low permeable or /and complicated reservoirs. And to promote the development of hydraulic fracturing theory.The theory of multiple fractures is very hard to study which is immethoding theory. A set of theoretical models has been established through comprehensive research :1 , According to the basic conception of elasticity mechanics and rock mechanics ,the mathematical model of shear stress root in the stress centralization around the perforations in deviated wellbores with perforations and the prediction model of hydraulic fracture initiation pressure and the location of fractures on the wellbore wall under different size of microannulus are established.Based on the principle of analogism,the estimation method of fracture initiation pressure inside the perforations is sought out. One theoretical model about the influence of a fracture on the initiation pressure of the adjacent perforations has been developed on the foundation of fracture mechanics. A formula is also be studied about the total turning angle from different local and direction in deviated wellbores.2, For the goal to investigate the feasibility of fracture link-up ,integrating elasticity mechanics,engineering mechanics,fracure mechanics and finite element method, using the new method of displacement discontinuity in building engineering ,this paper established three theoretic models including fracture edge stress model,the Displacement Discontinuity Method(DDM) and the Dislocation Parameter Model.Several methods are also presented to calculate the turning angel at the end of fracture. To analyze the fracture geometry paramerers and to estimate the likelihood of the link-up of fractures ,a set of approach is builded up.3, Based on the ordinary 2D mathematical model ,considering the fracture orientation and the changing of the confining stress in the near-wellbore region,the improved 2D mathematical model for fracture propagation and its detailed solution are established ,the main characteristic of which is to search corresponding prolongation time according to the length of every unit.