中高渗疏松砂岩水力喷射压裂水动力封隔特性

Simulation and feasibility analysis of hydrodynamic sealing in hydraulic jet fracturing of medium to high permeability unconsolidated sandstone

为确定海上疏松砂岩高渗透条件下水力喷射孔内流体增压特性是否满足岩石定点起裂条件,采用了计算流体力学方法,基于达西定律推导出速度与渗透率关系方程,建立了考虑岩石孔眼边界高渗条件下水力喷射孔眼内流体动力学模型,实验验证模型可靠,得出了地层渗透率、喷嘴压降、环空围压等关键参数对孔内流体增压的影响规律。结果表明,疏松砂岩高渗透性是降低其水力喷射压裂水动力封隔能力的关键因素,孔内流体增压值随储层渗透率升高呈现非线性递减;喷嘴压降与孔内流体增压值呈线性增加关系,但孔内流体增压值的增长斜率随储层渗透率升高而降低;环空围压对孔内流体增压值无显著影响;敏感性分析表明,影响孔内流体增压的参数排序:储层渗透率>喷嘴压降>环空围压。研究结果可为海上水力喷射压裂水力学参数优化设计提供理论依据。

In order to study the application of hydraulic jet fracturing technology in fine layering stimulation and transformation of low production and low efficiency wells in offshore medium and high permeability unconsolidated sandstone reservoirs,it is necessary to solve the problem of whether the fluid pressure characteristics in hydraulic jet holes still meet the fixed point fracturing conditions of rocks under high permeability conditions of unconsolidated sandstone.In this paper,the computational fluid dynamics method is used,and based on the relationship equation between velocity and permeability derived from Darcy′s law,the hydrodynamic model in the hydraulic jet hole considering the high permeability of the rock hole boundary is established.On the basis of the numerical model,different influencing factors(nozzle pressure drop,confining pressure,permeability)are set to study the variation law of fluid pressurization in the hole.And the simulation results were compared with previous indoor experimental results to verify the reliability of the model.The results indicate that nozzle pressure drop and rock permeability are the two main controlling factors affecting the pressurization of jet flow in porous sandstone formations,while annular confining pressure has no effect on the pressurization of jet flow in the hole.In actual working conditions,hydraulic jet fracturing needs to be carried out at a formation permeability of less than 8D to achieve pressure boosting effect.The research results can provide a theoretical basis for the application of hydraulic jet fracturing technology in offshore medium and high permeability reservoir fracturing and the optimization design of offshore hydraulic jet fracturing hydraulics parameters.