Fluid-solid Coupling Numerical Simulation Of Deliverability Of Screen Out Fracturing In Unconsolidated Sandstone Reservoir

Sand production is one of the major concerns in unconsolidated sandstone reservoir development. The screen out fracturing is a recently developed technology with high efficiency for sand control in foreign countries. It can both effectively control sand production, and significantly improve the production of fracturing wells with extensive application feasibility. However, the screen-out fracturing mechanism in unconsolidated sandstone reservoir is complicated, and to date, less is known about its intrinsic regularity.The unconsolidated sandstone reservoir has low consolidation strength. It shows strong stress sensitivity when the effective stress of reservoir changes. Considering the effect of fluid-solid coupling, systematic research was conducted on the intrinsic mechanism of the interaction between the seepage and deformation of unconsolidated sandstone, which is of great importance to understand the screen-out fracturing mechanism of unconsolidated sandstone and to offer guidance for screen-out fracturing implementation.Firstly, a stress-sensitivity experimental method, which can maintain the original pore throat configuration of unconsolidated sandstone, was established. Relevant tests were carried on the unconsolidated sandstone in the block of BinNan ShangEr, and the dynamic models of permeability and elastic modulus of unconsolidated sandstone reservoir are proposed. With respect to the fluid-solid coupling filtration theory, the governing equations of fluid-solid coupling model in permeability anisotropy reservoir were derived based on generalized Darcy's law and the assumption of small deformation of solid, and then combining relevant auxiliary equations, the fluid-solid coupling mathematical model for the artificial fracture-reservoir system in permeability anisotropy unconsolidated sandstone was established. Based on the Galerkin finite element method, the Galerkin finite element space discrete equations were derived from the governing equations of fluid-solid coupling, and differential discretion in time domain was done on the filtration equation with fully implicit format. The finite element solution equations of fluid-solid coupling model were established. On the base of discrete equations, the fluid-solid coupling finite element programs for single phase flow and two phase flow in unconsolidated sandstone reservoir were developed with FEPG.Secondly, the finite element analytical model for dynamic fracture creation in screen out fracturing was established. The process of dynamic fracture creation was simulated with dynamic boundaries of displacement and seepage pressure. The effects of the shape, size of created dynamic fracture and reservoir stress sensitivity on the physical parameters around the wellbore were analyzed for the screen-out fracturing well in unconsolidated sandstone reservoir. Research demonstrates that the dynamic fracture creation has noticeable influence on the effective stress and reservoir parameters near the fracture.Finally, with comprehensive consideration of the factors, i.e. the fluid-solid coupling effect, the dynamic fracture creation effect, the variable fracture conductivity and the reservoir permeability anisotropy, a new fluid-solid coupling model of deliverability analysis in screen out fracturing was established. The effects of each factor on the reservoir stress-strain, filtration property and after-fracturing production were analyzed. Research results show that the effective stress and physical parameters near the fracture change dramatically under the influence of fluid-solid coupling effect. The dynamic fracture creation has a noticeable influence on the strain and physical parameters near the wellbore. The permeability anisotropy has a noticeable influence on the alteration and distribution of effective stress and physical parameters of whole reservoir. It is an important factor affecting the deliverability of screen out fracturing. The stimulation ratio of screen out fracturing is lower than conventional seepage model under the combined influence of multiple factors, and the influence of multiple factors increases dramatically with the decrease of fracture length.The fluid-solid coupling issue of fracturing development in unconsolidated sandstone reservoir is studied in this thesis. Obtained research results are of great theoretical and applicable importance for the development of this type of reservoir.