Linear Composite Flow Model Of Fractured Horizontal Well

As the extent and difficulty of exploration increasing, reserves of oil and gas reservoirs with low-permeability in the proportion of total proven reserves become more and more large. People often use the method of multistage fractured horizontal well to improve the reservoir production in low-permeability oil fields. The seepage mechanism of fractured horizontal wells is that it can change the flow model from radial fluid to linear fluid. However, due to the existence of threshold pressure gradients(TPG) in low-permeability reservoirs, fluid flow deviates from the Darcy’s law and appears law of non-linear flow or pseudo-linear flow. In the process of unsteady-flow, propagation of pressure disturbance exists a moving boundary which will lead to heterogeneity and strong nonlinearity.This paper starts with the physical meaning and basic characteristics of the seepage process of low-permeability reservoirs. Considering the influence of TPG, we improves the definition of dimensionless pressure to eliminate the nonlinearity of diffusivity equation, then combines with the composite linear flow model to establish a bilinear-flow model of the vertical fractured well which considers the TPG, so we can respectively obtain the moving boundary pattern of different TPG and fracture conductivity in the conditions of constant pressure and constant production. In addition, we can also get wellbore pressure, the profile of reservoir pressure distribution and the profile of production.The calculation and analysis show that linear composition models can effectively simulate the model of vertical fractures with finite-conductivity in a rectangular reservoir. We compare the results with the exact solutions and it turns out that in early period the results match the exact solutions well, but in the middle flow stage it may appear differences on the flow model that the planar radial flow stage may not happen but be replaced by planar linear flow. In low-permeability reservoirs, the higher the TPG is, the slower the moving boundary spreads. In conditions of constant pressure, with the extension of time the moving boundary spreads outward, the moving boundary in the fracture?s midpoint spreads fastest and both sides gradually diminish. On the whole it is a curve of conical slope, and it will stop transmitting after reaching the maximum moving external boundary. When the maximum moving boundary is xm D =1.0/λD, the largest drainage area of the single well is yf(pi-pwf)/λ. The bigger the TPG is, the more steeply the pressure drop funnel is and the faster the production declines.Lastly, we respectively use ?Asymmetric Drainage Regions?, ?Three Regions? and ?Five Regions? to simulate horizontal well models of multistage fracturing, compare the results with that of numerical simulation and give the applicative scope of the model of analytical solution.