【作者】 曲连忠；

【导师】 程远方；

【作者基本信息】 中国石油大学 ， 油气工程力学， 2009， 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。疏松砂岩胶结强度弱,储层有效应力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,本文利用真三轴水力压裂模拟系统对弱胶结人工岩样进行了压裂模拟实验,研究了压裂排量、地应力组合、岩样胶结程度影响下的压裂压力及压后裂缝扩展形态;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,联立辅助方程,建立了渗透率各向异性疏松砂岩脱砂压裂人工裂缝-油藏系统流固耦合模型;基于Galerkin有限元法,对流固耦合方程进行了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;在有限元离散的基础上,基于FEPG系统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,建立了疏松砂岩近井物性参数分析模型,利用渗流压力及位移动态边界对钻井、开井生产、压裂动态造缝等过程进行了流固耦合模拟,分析了井眼效应、生产压差、造缝宽度等对近井储层孔渗参数及弹性参数的影响,研究表明上述因素均会对近井地带储层变形及物性参数分布产生显著影响。再次,建立了疏松砂岩油藏开井降压模型及脱砂压裂井出砂预测模型,优化了疏松砂岩油藏开井降压时间及脱砂压裂井临界生产压差。研究表明,控制开井降压时间可有效降低出砂危险,另外,脱砂压裂造缝压实区的形成可在一定程度上提高临界生产压差。最后,综合考虑流固耦合作用、裂缝导流能力变化、储层渗透率各向异性等建立脱砂压裂产能流固耦合模型,分析了各因素对储层物性参数及压后生产动态影响。研究表明,流固耦合作用会导致近裂缝区域储层有效应力及物性参数发生显著变化;裂缝导流能力随时间及空间的变化会对近裂缝储层物性参数分布及压后产能产生显著影响;储层渗透率各向异性会显著影响整个储层有效应力、物性参数分布及脱砂压裂井产能。本文对疏松砂岩油藏脱砂压裂相关问题进行了系统研究,其研究成果对该类油藏高效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, 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.更多还原