Research On Multi-crack Fracturing And Increasing Production Of Hydraulic Injection Holes

The surrounding low-permeability oilfields in Daqing has thin reservoirs,small inter-layers,large in-plane permeability difference,large in-plane phase transformation and narrow sand bodies(usually less than 300m)with scattered distribution.With the development of oilfields year after year,the effect of average single-well fracturing and oil increase has been deteriorating year by year.Therefore,this paper proposes a new method mainly through the combination of hydraulic injection radial drilling technology with auxiliary fracturing.The use of hydraulic injection radial drilling technology is not limited by the ground stress and can achieve horizontal drilling in any direction of the reservoir.Referring to the multi-fracture formation technology of horizontal wells,vertical wells form multiple parallel seams in the tunnel.Through theoretical research and field tests,the mechanism,position,shape and scale of multiple crack formation in the radial hole of hydraulic injection radial drilling is analyzed in-depth and a set of auxiliary radial fracturing assisted fracturing technology for low permeability oil fields in Daqing is established.The overall parameter optimization design method provides technical support for the development of peripheral low-permeability oilfields in Daqing.According to the stress distribution model near the hydraulic perforation hole and the rock fracture criterion,the fracture pressure profile along the well-bore is calculated.From the well-bore fracture pressure values at different well depths,the lower pressure may be occurred in deeper well due to the heterogeneity of the reservoir.Therefore,in the fracturing process,fracturing parameters should be reasonably selected to avoid the generation of multiple longitudinal cracks along the well-bore.The crack extension mathematical model is established by the elastic equation,fracturing fluid flow equation,fluid loss equation and proppant transport equation and crack propagation conditions.The factors affecting the crack extension is analyzed by the model.The influence of the drilling azimuth angle on the fracture pressure of the formation is obtained.Under the condition of spiral drilling,the fracture pressure of the formation increased with the increase of the relative azimuth of the perforation,which is not obvious compared with the directional drilling.Therefore,spiral drilling will greatly reduce the risk of overburden pressure due to imperfect drilling azimuth.By studying the effects of hole density,hole diameter,and depth of drilling on fracture pressure of the formation,it is found that the impact of drilling density on the fracture pressure is relativelysmall with respect to the azimuth of the drilling,and the hole density in the direction of the minimum azimuth must be greater than 3 to 4 when drilling.Finally,the directional hydraulic perforation assisted fracturing experiment is performed on 14 production wells and 11 injection wells in the field.The effective increase of oil in the 14 production wells is in the range of 37 t to 526 t and the effect of well injection change is also obvious.