Fractures' Stress Interference Research Of Tight Sandstone Reservoirs' Volume Fracturing

With the deep development of the tight sandstone reservoir,the tight sandstone reservoir that is buried deeply and is difficult to be produced gradually becomes the main target area of oil and gas development.The most effective treatment for the development of of tight sandstone reservoir is volume fracturing to enlarge the reservoir stimulation volume.Howerver,there has been no theoretical support for the refining design of tight sandstone reservoir's volume fracturing.Therefore,in this paper,based on new realization of indoor assessment parameters of geomechanics and monitoring and evaluation of scene's microseismic testing down the well,Stress interference analysis of fractures in the process of tight sandstone reservoir fracturing will be studied.Theroy and method of stress interference analysis of fractures of deepened tight sandstone reservoir fracturing process will be analyzed.At the meaningwhile,optimal design software of volume fracturing will be explored and has significant in the improvement of tight sandstone reservoir development.detailed contents research's detailed contents and main conclusions are as follows:(1)According to the tight sandstone reservoir's geological characteristics of Qian'an-Chang'ling lag in the southern Song'liao basin,650 times of experiments will be taken for 88 core samples.Such tight sandstone reservoir's physical parameters,mechanical properties,fracture development of such reservoir,in-situ stress,rock brittleness and compressibility will be analyzed.Then,a new method of evaluation will be put forward.Whereas the tight sandstone reservoir can be transformed with netword fractures mainly,nevertheless,the simulation's mechanism is very complex,there are a lot of factors that effect it,shearing sliping happens mostly in the process of fractures formation,rocks' friction characteristics has great influence on intial fracturing,fracture propagation and extension.Thus,frictional experiments will be carried out for the fracturing's shear effect in this paper.It is founded that the entrance of water and slick water reduces the friction level of rock samples and slip stability.Then self-supporting fractures are formed easily.Synthesizing compressibility,stress sensitivity,difference of in-situ stress,reduction of b value's friction coefficient,high quality reservoir wich has strong ability of stitching network can be optimized.It establishes the foundation of selection of layer for vlume fracturing of horizontal well and fracturing optimization design with fractures' interaction.(2)To obtain the fractures' roughly distribution of tight sandstone gas reservoir's volume fracturing,downhole microseismic fracture monitoring technique is carried out in the process of reservoir fracturing.Then,monitor the volume fracturing with fractures' interection of two horizontal wells and three vertical wells respectively,models of formation velocity and downhole microseismic fracture monitoring are established.Furthermore,inversion and interpretation are taken for the data of downhole microseismic fracture monitoring.And the distribution of fractures for the reservoir's construction of microseismic events.Direction and spatial distribution shape of fractures can be obtained at the meaningwhile.Moreover,the exsistance of fractures' interection in the process of fracturing is verified.Basing on the indoor experimentation,the actually in-situ data can be obtained furtherly.It provide technical support for the establishment of fractures' interection model and the model's parameters,the boundary condition setting,adjusting and optimizing and practical verification.(3)Basing on the block's geological features,physical properties of reservoir,mechanical properties,fractures developing situation,analysis of in-situ stress,rock brittleness,compressional characteristics and et al,combing fractures' distribution,stress interference of tight sandstone reservoir volume fracturing is studied in this paper.A two-dimensional vertical cracks inducing stress field is built.Combing stress equilibrium equation of rock and continuity equation of fluid,finite element equation and cohesive unit of pore pressure,fractures initiation and expansion,fluid tangential flowing inside fractures and normal filtration onside fractures are analyzed in this paper.The stress field near-wellbore under the condition of fracturing,the calculation of fracturing pressure,the calculation of layered rock's stress,the calculation of fracture size based on the models of PKN and KGD.Moreover,models of vertical well's stress interference finite element calculation,stress interference finite element calculation of horizontal well section multiple fracturing,double vertical wells' stress interference finite element calculation in the same block as well as the horizontal well are established in this paper.(4)Considering lots of influent factors of the tight sandstone reservoir volume transformation,these factors are analyzed by finite element numerical simulation.Fluid-solid coupling model is set up by pore unit inside the large-scale finite element software abaqus business.And the various influence factors on the influence law of sandstone reservoir stress interference of length and width of fracture and the sandstone reservoir stress.It is found that in-situ stress distribution oval in the fracture extension and perpendicular to the direction of fracture extension.With the increasing of injection pressure,hydraulic pressure on the fracture plane attenuation gradually slows down and the hydraulic pressure droping curve tends to smooth and fracture length increases linearly besides the approximate index increasing of maximum joint width of fracture.At the meaningwhile,the maximum fracture length decreases with the annual increase of fracturing fluid's viscosity and the maximum fracture width increases with the increase of the viscosity of fracturing fluid,while the fracture pressure is independent of the fracturing fluid viscosity.The maximum length and maximum width of fracture decrease with the increase of elastic modulus of reservoir.The maximum principal stress has no effect on fracture geometry.The maximum length and maximum width of fracture decrease with the increase of the minimum principal stress,and the crack pressure increases linearly at the meaningwhile.The pore water pressure increases rapidly to a critical value with the increase of permeability,then slowly increases to a critical value and decreases with the increase of permeability.The pore water pressure of reservoir increases with the increase of internal pressure,and its curve is close to a linear function curve.The pore water pressure increases rapidly to a critical value with the increase of the viscosity of the fracturing fluid,then decreases with the increase of the fracturing fluid viscosity.The pore water pressure of reservoir increases with the increase of seam length,and its curve is close to a linear function curve.(5)Considering the existence of the artificial fracture,the change of pore fluid pressure and physical parameters and et al,the stress field distribution with hydraulic fracture is changed as these factors as well as redirect phenomenon of gravity.Based on the platform of abaqus finite element software,the finite element model of the fracturing stress field of fluid-solid coupling is established to analyze the stress change of fracturing well.It is found that the dual effects of induced stress and the change of the pore pressure of the strata can affect the size and direction of the main stress.The maximum principal stress of the formation decreases gradually with the increase of the width of the fracture.With the increase of the length-width ratio of the fracture,the changing value of the minimum principal stress decreases rapidly and increases slowly soon afterwards.The larger difference value of the maximum and minimum principal stress,the smaller the steering distance and the smaller effect of induced stress field on the local stress field.The fracture spacing has significant influence on fracture morphology.The thinner the production layer,the higher the ratio of the fracture height extension and the height of the fracture will be far beyond the production layer.The thicker the production layer,the more easily the fracture height can be controlled within the production layer.When the production layer reaches a certain thickness,the fracture height is basically controlled within the production layer.And the optimal cluster's number of the horizontal well is optimized.On the basis of hydraulic fracturing calculation model and production forecasting model and formulas of tight sandstone oil and gas wells,"design of tight sandstone oil and gas well fracturing optimization and productivity prediction software" is compiled by Visual Basic computer language.Using the horizontal wells respectively and considering the interference of wells and sections' cluster under the condition of fractures' interference,the horizontal well sections' cluster spacing and fracture length can be optimized.To ensure the maximum fracture interference,the process of on-site construction and injection pumping are optimized.By underground micro seismic testing,the existence of the interference between fractures in the multi-port/cluster well fracturing construction is verified.At the same time,the accuracy of the model and practicality of results are verified.