赵建国,,
李智,
肖增佳,
贺艳晓,
赵皓,
任静
中国石油大学(北京)油气资源与探测国家重点实验室, 北京 102249
基金项目: 国家自然科学基金联合基金重点基金(U20B2015)，国家自然科学基金项目(41574103，41974120，41804104和U19B6003-04)，国家重大专项课题(2016ZX05004-003)和中国石油科技创新基金(2018D-5007-0303)资助
详细信息
作者简介: 欧阳芳, 女, 1992年4月生, 博士研究生, 主要从事地震岩石物理学研究.E-mail: FangOuyang92@163.com
通讯作者: 赵建国, 男, 1976年12月生, 现为中国石油大学(北京)地球物理学院教授, 主要从事地震波传播、数字岩芯、跨频段地震岩石物理实验技术与理论研究.E-mail: zhaojg@cup.edu.cn, jgzhao761215@aliyun.com
中图分类号: P631收稿日期:2020-09-11
修回日期:2020-12-08
上线日期:2021-03-10
Inversion of pore aspect ratio distribution based on effective medium theories
OUYANG Fang,ZHAO JianGuo,,
LI Zhi,
XIAO ZengJia,
HE YanXiao,
ZHAO Hao,
REN Jing
State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum(Beijing), Beijing 102249, China
More Information
Corresponding author: ZHAO JianGuo,E-mail:zhaojg@cup.edu.cn; jgzhao761215@aliyun.com
MSC: P631--> Received Date: 11 September 2020
Revised Date: 08 December 2020
Available Online: 10 March 2021
摘要
摘要:孔隙纵横比是描述多孔岩石微观孔隙结构特征的重要参数，目前用于获取岩石完整孔隙纵横比分布的经典模型为David-Zimmerman (D-Z)孔隙结构模型，该模型假设岩石由固体矿物基质、一组纵横比相等的硬孔隙以及多组纵横比不等的微裂隙构成，并认为固体矿物基质和硬孔隙均不受压力影响，在此基础上，利用超声纵横波速度的压力依赖性反演岩石硬孔隙和各组微裂隙的孔隙纵横比及孔隙度.该方法的关键点在于以累积裂隙密度为桥梁，借助等效介质理论建立了岩石弹性模量和孔隙纵横比之间的内在联系.但在D-Z模型中，多重孔隙岩石累积裂隙密度的计算直接由单重孔隙裂隙密度公式实现，这种近似导致该模型在许多情况下难以获得良好的反演精度.为了完善经典D-Z模型，本文提出了一种基于虚拟降压的孔隙纵横比分布反演策略，通过多个假想降压过程实现累积裂隙密度的准确计算，并将基于DEM和MT的经典D-Z模型推广到KT和SCA中，结合四种等效介质理论建立了一套完整的反演流程.采用一系列砂岩和碳酸盐岩样品，测试了反演流程在实际岩芯孔隙纵横比提取中的应用效果，研究结果表明：与D-Z模型相比，本文方法的模拟结果与实际数据吻合更好，并同时适用于砂岩和碳酸盐岩；此外，通过分析四种等效介质理论的模拟结果发现，本文方法并不十分依赖于等效介质理论的选择，这些理论获得的孔隙结构参数随压力的变化趋势基本一致，数值上仅存在略微差异，且这种差异随着压力的增大逐渐消失.本文方法是经典D-Z孔隙结构模型的重要补充，对岩石孔隙结构表征、流体饱和岩石速度预测以及孔间喷射流效应的模拟具有十分重要的意义.
关键词: 岩石孔隙结构/
孔隙纵横比/
虚拟降压/
等效介质理论
Abstract:The pore aspect ratio is an important parameter to describe pore structure characteristics of porous rocks. At present,the most classical model used to obtain complete pore aspect ratio distribution of rocks is the David-Zimmerman (D-Z) pore structure model. The model assumes that the rock is composed of solid mineral matrix,a group of stiff pores having the same aspect ratio and a distribution of micro-cracks with different aspect ratios,in which the material matrix and stiff pores are pressure-independent. Based on the assumptions,the pore aspect ratio and porosity of stiff pores and micro-cracks are extracted from the pressure dependence of ultrasonic velocities. The key point of this method is that the cumulative crack density is taken as a bridge to establish the intrinsic relationship between rock elastic modulus and pore aspect ratio through effective medium theory. However,in the D-Z model,the cumulative fracture density of multi-porosity rock is directly calculated using the formula of crack density theoretically only applicable for rock with a single pore type,which makes it difficult to achieve good inversion accuracy in many cases. In order to improve the classical D-Z model,this paper proposes an inversion method for calculating pore aspect ratio distribution using thought experiment. In this method,the cumulative crack density is accurately computed through a fictitious unloading path,and the classical D-Z model based on DEM and MT is extended to the case of KT and SCA. As a result,a detailed inversion workflow combining with four effective medium theories is established. This workflow is applied in the aspect ratio distribution extraction for a set of sandstones and carbonate samples to illustrate the capability of the method. The results show that the proposed method is in better agreement with the actual data as compared to the D-Z model,and can be applied to both sandstone and carbonate samples. In addition,the proposed method is almost independent of the selection of the effective medium theories. The pore structure parameter obtained from the four theories changes with pressure in a similar way. Although there is a slight difference in these results,it gradually disappears with increasing pressure. Our method is an important supplement to the classical D-Z pore structure model. It is of great significance in the characterization of rock pore structure,prediction of fluid saturated rock velocity and simulation of pore-scale squirt flow.
Key words:Pore structure model of rock/
Pore aspect ratio/
Fictitious unloading method/
Effective medium theory
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