Study On Law Of Fracture Propagation Of Radial Well Fracturing In Low Permeability Heavy Oil Reservoir

The technology combined radial well and hydraulic fracturing has been applied in various oil fields and achieved effective output.The advantages of radial well fracturing in economy and stimulation effect are obvious when compared to horizontal well fracturing and conventional perforation fracturing.Radial well hydraulic fracturing technology can effectively improve the utilization of the reservoir area,and more applicable in production and development of thin reservoir.However,the fracture morphology and propagation law of radial well fracturing are still remain unclear,which limits the development and application of radial well fracturing.The column coordinates establishment of borehole and borehole radial stress distribution model,the tensile fracture criterion to predict crack initiation,and model was imported for programming examples of calculation and analysis,obtained under different conditions of the near wellbore with the maximum principal stress distribution drawing maximum principal stress curve,the analysis of influence of parameters on the crack.Through theoretical analysis and experiment,the conclusion: whether external conditions how to change the optimal location of the crack is still in the radial well.Based on fluid-solid coupling equation,factors that different parameters of radial well on crustal stress were solved nonlinearly by using ABAQUS.Initial fracturing position and propagation morphology were identified according to maximum tension-stress criterion.The conclusions stated that in-situ stress field distribution was changed during the radial well fracturing and the induced stress field along the radial well is established at the same time.The stage of fracture propagation is simulated by extended finite element method(XFEM)in ABAQUS.Initial fracturing position and propagation morphology were identified according to maximum tension-stress criterion and maximum energy release rate fracture criterion.Results obtained from 3D physical experiment in the laboratory were used to verify the accuracy of simulation to a certain degree.The propagation of major fracture is orientated by the induced stress in a certain area.The distance of orientated fracture is able to 40 meters.The guiding function of fracture orientated propagation is evaluated by included angle ? between the axis of radial well and equivalent fracture.The smaller the value of ? is,the better effect of fracture orientated propagation is.The increase of horizontal stress difference and decrease of vertical density of radial wells are unfavorable to decrease the value of ?.The failure pressure grows up with the azimuth angle of radial well increasing.Also the degree of different parameters influence on value of ?,failure pressure and maximum fracture width is ranked by grey correlation method.Fracture morphology under three cases(single radial well,vertical multi-radial wells and horizontal multi-radial wells)were identified.The effect of fracture orientated propagation could be strengthen greatly by the design of vertical multi-radial wells.The minor fracture is generated in the interference stress field and connect the two nearby radial wells.With the combination of major fracture and minor fracture,the oil drainage area is improved and the oil flow resistance near the wellbore is decreased greatly.At last the perforation scheme of radial wells is optimized according to the results of simulation.The results of research can be referred to prediction of fracture propagation and design of radial well completion or fracturing.The technology of radial well fracturing combined with steam soak is suitable for tight heavy oil formation.The thermal deliverability of radial well is researched by simulation based on the results above.The results show that multi-cracks morphology is performed under the multi radial wells which increase the drainage area.The thermal deliverability in 3 years of radial well fracturing is 2.65 times larger than that of regular fracturing.Also the parameters of steam soak are optimized.The conclusion is significant and important for the field.