砾岩油藏渗透率各向异性成因机理及微观控制因素研究

The conglomerate reservoir is a kind of complex petroleum reservoir formed under special sedimentary conditions of near source, multi-streams and rapidly changing, above sedimentary environment lead to very strong heterogeneity and multi-modality pore structure characteristics which the reservoir permeability network formed by three types of particles include to conglomerate, sand and shale influence the reservoir physical properties. Therefore, the study on genetic mechanism of permeability anisotropy and its micro-control factors become the basis and premise of high effective development for conglomerate reservoir. In this fund, the conglomerate reservoirs of Mahu block in Xinjiang is selected as research object to reveal genetic mechanism of permeability anisotropy. Firstly, the following core experimental methods such as CT scanning, constant velocity mercury injection, casting thin section, scanning electron microscope and nuclear magnetic resonance are comprehensively applied to analyze the effects of directional arrangement of sedimentary particles, distribution form of clay minerals and seepage path on permeability in different directions, so as to clarify the formation mechanism of permeability anisotropy for multi-modality conglomerate reservoir. Based on above analysis, the micro-pore structure parameters are optimized to analyze the influence weights of each parameter on permeability in different directions by data mining methods, and then determine the micro-dominant factor of permeability anisotropy and establish its quantitative calculation model. Finally, according to the geologic model determined by genetic mechanism research and the mathematical model established by data mining research, the numerical simulation method is used to analyze the amplitude and characteristic of permeability changing in order to reveal the evolution rule of permeability anisotropy for multi-modality pore structure conglomerate reservoir. Above research results can provide geological basis for the effective development of conglomerate reservoirs.

砾岩油藏由于多物源、多水系、快速多变的沉积环境导致储层非均质性极强，孔隙结构呈现复模态特征，即砾、砂、泥三级颗粒形成的渗流通道影响储层物性，其渗透率各向异性成因机理及微观控制因素的研究，是该类油藏能够高效开发的基础和前提。本基金以新疆玛湖地区砾岩储层渗透率的研究为切入点，综合利用CT扫描、恒速压汞、铸体薄片、扫描电镜、核磁共振等岩心实验方法，分析沉积颗粒定向排列、黏土矿物分布形式、流体渗流路径等因素对不同方向渗透率的影响，明确复模态砾岩储层渗透率各向异性的形成机制；进而，优选微观孔隙结构参数，利用数据挖掘方法分析每种参数在不同方向上对渗透率的影响权重，确定渗透率各向异性的微观主控因素，并建立各向异性的定量计算模型；在此基础上，基于成因机理研究确定的地质模型和数据挖掘研究建立的数学模型，利用数值模拟方法分析不同方向渗透率的动态变化幅度和变化特征，揭示复模态砾岩油藏渗透率各向异性的演化规律。

砾岩油藏由于近物源、多水系和快速多变的沉积环境导致储层非均质性极强，孔隙结构具复模态特征，使其呈现特殊的渗流规律和较强的各向异性，进而影响孔隙原油的驱替方式和最终采收率，明确渗透率各向异性的成因机理及控制因素，是砾岩油藏能够高效开发的前提。本基金以克拉玛依油田典型砾岩储层为研究对象，依据密闭取心资料优选8块砾岩样品，在现场切割和实验室制备的基础上，制作成边长为4.5cm的标准立方体样品，综合利用铸体薄片、CT扫描、恒速压汞等实验方法对其进行研究。研究结果表明，沉积作用和水动力条件控制着渗透率各向异性的分布规律，矿物颗粒的分选、磨圆、排列方式及沉积结构面的发育影响不同方向的渗流路径和渗流阻力，导致渗透率呈现较强的各向异性，平行水流方向的渗透率最大，垂直水流方向的次之，而垂直沉积方向的渗透率受到渗流迂曲度、孔喉连通性及沉积结构面等因素的综合影响，渗透率最小。另外，后期的成岩作用通过改变储层的微观孔隙结构，降低不同方向渗透率的绝对值以及渗透率各向异性的强度，但不会改变渗透率各向异性的分布规律。在此基础上，利用数据挖掘方法对8块样品不同方向微观孔隙结构参数与渗透率标准方差的数据集进行分析，相对分选系数对渗透率标准方差的影响权重最大，孔喉大小分布的均匀程度是渗透率各向异性强度的微观主控因素，均匀程度越差，渗透率各向异性越明显；平均毛管半径、迂曲度、最大孔喉半径的参数权重次之，为次要控制因素，其他微观孔隙结构参数对渗透率各向异性有影响，但影响程度有限。在明确微观渗流规律各向异性的基础上，依据微观孔隙结构参数和黏土矿物对化学剂吸附滞留量的差异，将储层类型进行合理划分，其中，水驱和聚/表二元驱两种驱替方式下储层均被细分为4类；进而确定了不同储层类型水驱和聚/表二元驱微观孔喉原油的动用规律，明确了化学驱剩余油的启动机制，建立了油藏采收率计算模型，可以准确预测不同驱替方式、不同驱替阶段油藏的最终采收率。