Study On The Law Of Fracture Initiation And Propagation And Productivity Prediction For Radial Well-fracturing

As a new means to increase production of oil and gas fields,the hydraulic fracturing technology of combined with radial well has achieved gratifying results in Jiangsu,China Shengli,Liaohe oil field.At present,the study on the law of fracture initiation and propagation and productivity prediction for radial well-fracturing is less research data,and the technology needs theory support.Recognizing the radial well fracture initiation and the influence of frcature propagation form on oil and gas production has important significance for optimizing the parameters of radial well completion and fracturing design and predicting the capacity of radial well after hydraulic fracturing.On the basis of conservation of mass law and momentum conservation law and considering the power-law fluid viscosity and compressibility,a pressure wave transmitting mathematical model in radial well has be established for understand the pressure distribution in radial well.The mathematical model is verified through physical experiment(time difference method),and the influence of different performance parameters on the velocity of pressure wave is analyzed.Considering the radial hole length is much smaller than the value of pressure wave velocity,we believe that the pressure wave moment communicates to the radial well toe.Using the finite element software Abaqus as a platform,considering the rock mass fluid-solid coupling effect and the phenomenon of stress concentration after straight well and radial well rock with initial stress drilling and removing from the reservoir,a 3 dimensional fracture model of radial well was established.The influence of seven factors on fracturing pressure and initiation position was studied in the normal fault stress mechanism or in strike slip fault mechanism.Research results show that initiation pressure gradually increased with the increasement of radial well azimuth,reservoir permeability,rock young's modulus and the reduction of radial hole length,diameter,horizontal stress difference and Poisson's ratio in the fault stress mechanism,and vice versa.Easy initiation zone in the radial wells toe is most likely to generate along with the horizontal stress difference increasement,and other factors had little effect.Meanwhile,the initiation pressure gradually increased with increasing of radial length,diameter,radial well azimuth angle,reservoir permeability,rock modulus and the reduction of horizontal stress difference and rock Poisson ratio decreases in the slip fault stress mechanism,and vice versa.Easy initiation zone in the radial wells toe is most likely to generate along with the horizontal stress difference increasement,and other factors had little effect.Whether the fault stress mechanism or the slip fault stress mechanism,the initiation point has always been near vertical well bore in the range of parameters.Based on the the extended finite element theory,considering the fluid-solid coupling effect and the interference effect of radial wells guide on hydraulic fracture,a 3D hydraulic fracturing propagation numerical simulation guided by single radial well and another 3D hydraulic fracturing propagation numerical simulation guided by multiple radial wells were built.For single radial well,the simulation results show the influence ability of various factors on hydraulic fracture is different and the order from large to small is the horizontal stress difference,radial well azimuth,radial well radial diameter,radial well length,fracturing fluid displacement,rock Young's modulus,reservoir permeability,fracturing fluid viscosity,rock Poisson ratio.For multiple radial wells,the simulation results show the influence ability of various factors on hydraulic fracture is different and the order from large to small is radial wells azimuth,fracturing fluid displacement,the horizontal stress difference,rock Young's modulus,fracturing fluid viscosity,radial wells radial diameter,radial wells spacing,reservoir permeability,radial wells length,rock Poisson ratio.Through vertical arrangement of radial wells can produce more guiding force compared with the single radial well and result in hydraulic fracture propagation along the favorable region.Hydraulic fracturing capacity of radial well and multiple radial wells was predicted and evaluated under different parameters.Analysis results show that under the same conditions,the hydraulic fracturing capacity of multiple radial wells is more higher than single radial well.For the hydraulic fracturing model with single radial well,the cumulative production change effected by levels' change from big to small is as follows: radial well length,radial well azimuth,radial well radial,fracturing fluid displacement,the horizontal stress difference,fracturing fluid viscosity,reservoir permeability,rock Poisson ratio,rock Young's modulus.It shows that the change of radial well length had marked effect on productivity.For the hydraulic fracturing model with multiple radial wells,the cumulative production change effected by levels' change from big to small is as follows: radial wells azimuth,radial wells length,fracturing fluid viscosity,reservoir permeability,fracturing fluid displacement,the horizontal stress difference,radial wells radial,rock Poisson ratio,rock Young's modulus,radial wells spacing.It shows that the change of radial wells azimuth had marked effect on productivity.When predict and evaluat the production capacity by Guiding factor,there will be a small amount of error.Because the guiding factor cannot consider the distribution of hydraulic fracture and residual oil area.It can make up for the evaluation lack from guidance factor by productivity prediction to evaluate the economic benefits of radial well hydraulic fracturing.