【作者】 赵益忠；

【导师】 程远方；

【作者基本信息】 中国石油大学 ， 油气工程力学， 2008， 博士

【摘要】 出砂是疏松砂岩油藏开发面临的主要难题之一。脱砂压裂技术是国外近年来发展起来的一种高效防砂技术,该技术既能有效控制出砂,又能显著提高压裂井产量,应用前景极为广泛。然而疏松砂岩油藏脱砂压裂机理复杂,目前对其内在规律认识还不够深入。疏松砂岩油藏胶结强度弱,当储层有效应力状态改变时,具有很强的应力敏感性。因此,考虑流固耦合作用影响,系统研究疏松砂岩渗流与变形相互作用的内在机制,对认识疏松砂岩油藏脱砂压裂机理及指导脱砂压裂施工具有重要意义。首先,本文建立了保持疏松砂岩原位孔隙结构的应力敏感性实验方法,对滨南尚二区疏松砂岩进行了应力敏感性实验,建立了疏松砂岩油藏渗透率及弹性模量动态模型;在流固耦合渗流理论基础上,基于广义达西定律及固体小变形假设推导了渗透率各向异性储层流固耦合控制方程,再联立相应辅助方程,建立了新的渗透率各向异性疏松砂岩脱砂压裂人工裂缝-油藏系统流固耦合数学模型;基于Galerkin有限元法,对流固耦合模型控制方程进行了Galerkin空间域离散,并按全隐式格式对渗流方程进行了时间域差分离散,推导建立了流固耦合模型有限元求解公式;在有限元离散的基础上,基于FEPG软件自主开发了疏松砂岩油藏单相及两相渗流流固耦合有限元程序。其次,建立了脱砂压裂动态造缝有限元分析模型,利用位移及渗流压力动态边界对动态造缝过程进行了流固耦合有限元模拟,分析了造缝形态、裂缝尺寸及储层应力敏感程度对疏松砂岩脱砂压裂井近井地带物性参数的影响规律,研究表明脱砂压裂动态造缝会对近裂缝区域储层有效应力及物性参数产生显著影响。最后,本文综合考虑流固耦合作用、动态造缝效应、变裂缝导流能力、储层渗透率各向异性等因素,建立了新的脱砂压裂产能流固耦合分析模型,分析了各因素对储层应力应变特征、储层孔渗特性变化及压后生产的影响。研究表明,在流固耦合作用下,近裂缝区域储层有效应力及物性参数会发生显著变化;动态造缝效应主要对近井眼储层的应变特性及物性参数产生显著影响;储层渗透率各向异性会显著影响整个储层有效应力及物性参数变化及分布,是影响脱砂压裂产能的重要因素;在多因素综合影响下,脱砂压裂增产倍数明显低于常规渗流模型计算结果,且缝长越小,各因素综合影响越显著。本文对疏松砂岩油藏脱砂压裂开发中的流固耦合问题进行了系统研究,得到的研究成果对该类油藏开发具有重要的理论和应用价值。更多还原

【Abstract】 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.更多还原