Experimental Study On Stress Sensitivity Of Horizontal Joints And Calculation Of Capacity In Extra - Low Permeability Sandstone Reservoirs

Ultra-low permeability reservoir development needs of hydraulic fracturing, in the shallow reservoir forms horizontal fracture, and this type of reservoir itself contains natural micro-cracks, such as our Daqing Oilfield, Yanchang Oilfield and so on. In the oil field development process with the formation pressure drop, matrix permeability and fracture conductivity decreased, there is a large difference between considering the stress-sensitive or not, such as production capacity, degree of recovery, the formation pressure. In addition, stress sensitivity experiments test methods and evaluation methods still need to be improved, the capacity calculation of fractured horizontal reservoir considering the stress sensitivity needs further study.Firstly, studies the theory of stress sensitivity to determine the rock compressibility and the rock effective stress coefficient; On the basis of theoretical research carry out the matrix core and horizontal fracture core stress sensitive tests and influencing factors analyse; Finally, the stress sensitivity experiment models are applied to reservoir engineering and numerical simulation, the impact of stress sensitivity and horizontal fracturing parameters are analyzed on vertical well production capacity and other development indicators.This article mainly achieved the following understanding:(1) Deduced the new formula of rock pore compressibility, rock porosity associated with effective stress coefficient compression, rock pore compressibility reduced along with porosity decreases.(2) Presents a simple effective stress coefficient theoretical calculation and a simple effective stress coefficient experiment method. The effective stress coefficient is only related to the size of porosity and poisson’s ratio, rock porosity and poisson ratio can be directly used to calculate the effective stress coefficient.(3) Stress sensitive laboratory tests preferably by the modified effective stress coefficient method given fixed confining pressure and changing internal pressure that can accurately evaluate the reservoir stress sensitivity, using the equivalent effective stress even can be converted high-pressure reservoir into low pressure laboratory conditions.(4) Taking the effective stress of the original reservoir as the starting point, all the sensitivity degrees of the extra-low-permeability cores are moderate and weak. The extra-low-permeability cores with horizontal fracture are strong, permeability sharply decline when confining pressure increase and permeability recovery low with confining pressure decrease until the starting point.(5) Temperature from30℃to150℃rock permeability impairment increased3.8%, the stress-sensitive intensity slightly increases with increasing temperature. Moreover, slippage effect, timeliness and displacing pressure impact stress-sensitive laboratory tests.(6) Derived a horizontal fractured vertical well productivity calculation formula considering stress sensitivity,which can accurately be applied to X oilfield productivity calculation, the relative error is smaller than existing horizontal fractured vertical wells productivity calculation formula.(7) Analysis of results by X-Oilfield numerical simulation:Best fracture penetration ratio is0.5; best fracture conductivity is15D-cm; the optimum number of fractured horizontal fracture is1/4m; horizontal fracture shape is not importantto well productivity; the horizontal iiacture syminetry impacts greater in the early stage and smaller in the late.Only considering a single permeability stress sensitivity,the oil production and cumulative oil production all reduce.