Experimental And Numerical Simulation Research Of Screen Out Fracturing In Unconsolidated Sandstone

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, the fracturing simulation experiment is conducted by a triaxial rock mechanics test system with weakly consolidated artificial core sample, and the fracture geometry and the law of fracturing pressure varying with time are researched under the influence of fracturing flow rate, ground stress and degree of cementation. 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 fluid-solid coupling equations, and differential discretion in time domain was done on the filtration equation with fully implicit format. 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 analytical model for reservoir parameters near wellbore in unconsolidated sandstone was established. The fluid-solid coupling simulation of the process, i.e. the drilling, the production and the dynamic fracture creation was conducted with dynamic boundaries of displacement and seepage pressure. The effects of the wellbore effect, drawdown pressure and fracture width on the poroperm parameters and elastic parameters around the wellbore were analyzed. Research demonstrates that the above factors have noticeable influence on the reservoir deformation and reservoir parameters in the immediate vicinity of wellbore.Thirdly, the models for the pressure release and the prediction of sand production of screen out fracturing well were established, and the time of pressure release and the critical drawdown pressure of screen out fracturing well were optimized. Research demonstrates that the danger of sand production decreases through controlling the time of pressure release. The critical drawdown pressure increases because of the formation of compaction zone in the fracture creation in screen out fracturing.Finally, with comprehensive consideration of the factors, i.e. the fluid-solid coupling effect, the variable fracture conductivity and the reservoir permeability anisotropy, a fluid-solid coupling model of deliverability analysis in screen out fracturing was established. The effects of each factor on the 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 conductivity varying with time and space has a noticeable influence on the deliverability and the distribution of physical parameters near the fracture. The permeability anisotropy has a noticeable influence on the deliverability and the distribution of effective stress and physical parameters of whole reservoir.The relevant issue of screen out fracturing in unconsolidated sandstone reservoir is studied systematically in this thesis. Obtained research results are of great theoretical and applicable importance for the high efficiency development of this type of reservoir.