Study On Productivity Evaluation And Fluid Flow Mechanism Of Low-permeability And Tight Reservoir With Multi-stage Fracturing Horizontal Well

Multi-stage fracturing horizontal well has gradually become the leading technology in the effective development of low permeability and tight reservoir. By methods of reservoir engineering and numerical solution, steady-state and unsteady-state models for multi-stage fracturing horizontal well in low permeability and tight reservoir were established, based on which the productivity and fluid flow mechanism of multi-fracture system were thoroughly studied. The main research results are summarized as follows:1. Steady-state model for multi-stage fracturing horizontal well in low permeability and tight reservoir was established. Characteristics of fracture-controlled productivity were studied. The results indicate that the calculation productivity of the new model which considers the nonlinear flow is between that of Darcy’s linear flow model and pseudo threshold pressure gradient model. Pressure drop in the wellbore of horizontal well for low permeability and tight reservoir is not significant and fracture-controlled productivity varies from the heel to the end which is low in center while high in edges.2. The fractured horizontal well productivity viscously increases with the number, length and conductivity of hydraulic fractures. Based on the steady-state model, the optimization of number, half-length and conductivity of hydraulic fractures were achieved which can provide theoretical guidance to the productivity evaluation and fracturing parameters optimization of the actual production.3. Unsteady-state model for multi-stage fracturing horizontal well in low permeability and tight reservoir was established. Productivity decline of multi-fracture system was studied by the established model. The results indicate that the productivity of fractures will be equal in the symmetric positions and the total productivity of fractured horizontal well viscously declines over production time in the circumstance of constant bottom hole pressure.4. The characteristics of the pressure field and pressure gradient field distribution of multi-fracture system were presented by the established model. The results indicate that there exist four flow regimes in the reservoir with fractured horizontal well, namely fracture-linear flow, fracture-radial flow, reservoir-linear flow and system-radial flow.5. The effects of heterogeneous distributions and unequal half-length of fractures on the productivity of multi-stage fracturing horizontal well were studied. The results show that multi-stage fracturing horizontal well with uniformly-distributed fractures has higher productivity than that with heterogeneously-distributed fractures. Fracture-pattern of "dense inside and disperse outside" yields a higher productivity than pattern of "disperse inside and dense outside" and fracture-pattern of "short inside and long outside" yields a higher productivity than pattern of "long inside and short outside" in the case of constant total fracture-length. Therefore, in the optimization of multi-stage fracturing horizontal well, fractures should be uniformly distributed along the wellbore and long near the edges while short near the center, which would be beneficial to the stimulation of multi-stage fracturing horizontal well.