风城油田齐古组油砂细观结构和渗流特征

Study on Meso⁃Structures and Flow Characteristics of Oil Sands in Qigu Formation of Fengcheng Oilfield

为确定风城油田侏罗系齐古组油砂的细观结构和渗流特征,利用微米CT获得的灰度图像,在传统图像分割方法的基础上,提出了适用于油砂的3种介质图像分割方法,并采用物理实验法获得了油砂数字岩心,构建了孔隙网络模型。研究表明:在构建油砂数字岩心时,需要在多孔介质图像二值化方法的基础上提出适用于油砂的3种介质图像分割方法,来区分油砂中的颗粒、沥青质和孔隙;代表性体积单元的边长不小于3.0 mm时,所建立的数字岩心才能较为真实地反映油砂的细观结构;风城油田侏罗系齐古组油砂颗粒与沥青质的接触方式主要分为颗粒接触、胶结和悬浮3种,且风城油田油砂具有较强的非均质性和各向异性,沥青质作为骨架的一部分或作为孔隙流体,绝对渗透率比有效渗透率高约2个数量级,其相态显著影响油砂的细观结构。

In order to clarify the mesostructures and flow characteristics of oil sands in the Jurassic Qigu formation in Fengcheng oilfield,a threemedium image segmenting method suitable for oil sands was proposed by using micron CT grayscale images and conventional image segmenting method.Using the new method,digital oil sand cores were obtained from physical experiments,and finally a pore network model was built.The research shows that when constructing digital oil sand cores,it is necessary to propose a threemedium image segmenting method suitable for oil sands on the basis of the binary image segmenting method for porous media,to distinguish the particles,asphaltenes and pores in oil sands.Only when the side length of the representative volume unit of a digital core is greater than 3.0 mm,it can truly reflect the mesostructures of oil sands.The contact between particle and asphaltene in the oil sands of the Jurassic Qigu formation in Fengcheng oilfield are divided into three types:particle contact,cementing contact and suspending contact.Furthermore,the oil sands are strongly heterogenous and anisotropic,and asphaltene as a part of framework or as pore fluid,its absolute permeability is about 2 orders of magnitude higher than the effective permeability.As a result,the phase state of the asphaltene significantly affects the mesostructures of the oil sands.