Microscale Pore Throat Differentiation and Its Influence on the Distribution of Movable Fluid in Tight Sandstone Reservoirs

Fengjuan Dong,Zeyong Sun,Yuan Cao,Xuefei Lu,Xinjiu Rao,Feng Xiong

doi:10.1155/2021/6654773

Abstract

Tight sandstone reservoirs have small pore throat sizes and complex pore structures. Taking the Chang 6 tight sandstone reservoir in the Huaqing area of the Ordos Basin as an example, based on casting thin sections, nuclear magnetic resonance experiments, and modal analysis of pore size distribution characteristics, the Chang 6 tight sandstone reservoir in the study area can be divided into two types: wide bimodal mode reservoirs and asymmetric bimodal mode reservoirs. Based on the information entropy theory, the concept of “the entropy of microscale pore throats” is proposed to characterize the microscale pore throat differentiation of different reservoirs, and its influence on the distribution of movable fluid is discussed. There were significant differences in the entropy of the pore throat radius at different scales, which were mainly shown as follows: the entropy of the pore throat radius of 0.01~0.1 μm, >0.1 μm, and <0.01 μm decreased successively; that is, the complexity of the pore throat structure decreased successively. The correlation between the number of movable fluid occurrences on different scales of pore throats and the entropy of microscale pore throats in different reservoirs is also different, which is mainly shown as follows: in the intervals of >0.1 μm and 0.01~0.1 μm, the positive correlation between the occurrence quantity of movable fluid in the wide bimodal mode reservoir is better than that in the asymmetric bimodal mode reservoir. However, there was a negative correlation between the entropy of the pore throat radius and the number of fluid occurrences in the two types of reservoirs in the pore throat radius of <0.01 μm. Therefore, pore throats of >0.1 μm and 0.01~0.1 μm play a controlling role in studying the complexity of the microscopic pore throat structure and the distribution of movable fluid in the Chang 6 tight sandstone reservoir. The above results deepen the understanding of the pore throat structure of tight sandstone reservoirs and present guiding significance for classification evaluation, quantitative characterization, and efficient development of tight sandstone reservoirs.

Highlights

In recent years, with the development of the economy, people’s demand for energy consumption has been promoted, and the improvement of oil and gas exploration and development technology and theoretical innovation have been promoted, expanding the field of unconventional oil and gas exploration and development [1]
Taking the Chang 6 tight sandstone reservoir in the Huaqing area of the Ordos Basin as an example, the microscale pore throat differentiation of different reservoirs and its influence on the distribution of movable fluid in tight sandstone reservoirs are analyzed based on casting thin sections, nuclear magnetic resonance (NMR) experiments, modal analysis, and information entropy theory
The pore structure of the reservoir refers to the geometry, size, distribution, and interconnection of pores and throats of the rock, as well as the frequency distribution pattern of the pore throat radius

Summary

Introduction

With the development of the economy, people’s demand for energy consumption has been promoted, and the improvement of oil and gas exploration and development technology and theoretical innovation have been promoted, expanding the field of unconventional oil and gas exploration and development [1]. Tight sandstone reservoirs are currently one of the “hot spots” in petroleum exploration and development Their microscopic geological characteristics, pore throat genetic mechanisms, distribution heterogeneity characteristics, and fluid seepage mechanisms are different from those of conventional and general low permeability reservoirs [2, 3]. The pore throat sorting coefficient is close to 0, and the pore throat size distribution can be regarded as qualitatively uniform, which is contradictory to the essential characteristics of tight sandstone reservoirs with complex microscopic pore structures and strong heterogeneity. These parameters cannot accurately reflect the heterogeneity of the micropore structure of tight sandstone reservoirs. This study has important theoretical and practical significance for promoting the efficient development of tight oil and gas reservoirs

Experiments and Methods

Discussion

Conclusions