Study on Heterogeneity of Pore Throats at Different Scales and Its Influence on Seepage Capacity in Different Types of Tight Carbonate Reservoirs

Chunyan Qi,Yan Shen,Hai Huang,Xing Yang,Fengjuan Dong,Yun Liu,Xixiang Liu,Chun Zhu

doi:10.1155/2020/6657660

Chunyan Qi, Yan Shen + Show 6 more

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https://doi.org/10.1155/2020/6657660

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Abstract

The carbonate reservoirs in the middle Sichuan area have undergone complicated tectonics, resulting in various types of reservoir space, large secondary changes, and multiple complexities. Taking the tight carbonate gas reservoir of the Deng-4 member in this area as an example, based on casting thin sections, scanning electron microscopy, and high-pressure mercury injection experiments, the reservoir space and microstructural characteristics of the micropore throats were studied, and the influence of the microscale heterogeneity in different types of reservoirs on the seepage capacity was analyzed by applying fractal theory. The results showed that the reservoir space in the tight carbonate rock of the Deng-4 member in the study area could be divided into 3 types: pore-hole-fracture, pore-hole, and pore types. The distribution characteristics of the pore throat diameter were multimode wide type, double-mode high and low asymmetrical type, and single-mode concentrated type. The fractal dimension and seepage capability of the pore throat increased successively in sizes from less than 0.1 μm to 0.1~1.0 μm and greater than 1.0 μm. On the one hand, the development of karst caves and fractures controlled the percolation ability of tight carbonate reservoirs; on the other hand, it enhanced the heterogeneity of the micropore throat structure. However, the development degree of dissolved pores and microfractures has a weak contribution to the connectivity and seepage capacity of the reservoir space. Acidification, fracturing, and other measures can be adopted to enhance the connectivity between pores to improve the productivity of the gas reservoir. This study provides a scientific basis for the efficient exploration and development of tight carbonate reservoirs.

Highlights

The structure of pore throats directly controls the adsorption capacity and seepage characteristics of a reservoir and affects the hydrocarbon production capacity of the reservoir [1]
Taking the tight carbonate reservoirs of the Deng-4 member in the central Sichuan basin as an example, in this study, we analyzed the correlations among the porosity, permeability, permeability contribution, and fractal dimension of pores at different scales, which were calculated based on fractal theory and data from experiments with casting thin sections, scanning electron microscopy, and high-pressure Hg injection to provide a theoretical basis for the exploration and development of tight carbonate gas reservoirs
The complex sedimentary, diagenetic, and tectonic superposition transformation of carbonate reservoirs creates complicated reservoir spaces and leads to the obvious heterogeneity in different kinds of reservoirs or various scales of pore throats. (Carbonate reservoirs developed complicated reservoir spaces, leading to the obvious heterogeneity of pore throats at different scales or in various kinds of reservoirs.) These features imply the necessity of quantitatively expressing the porosity and throat heterogeneity of tight carbonate reservoirs in the Deng-4 member in the central Sichuan basin with the technology of high-pressure Hg injection

Summary

Introduction

The structure of pore throats directly controls the adsorption capacity and seepage characteristics of a reservoir and affects the hydrocarbon production capacity of the reservoir [1]. Many theories and methods about rock pore structure and its evolution and fluid seepage simulation have emerged, and some achievements have been made [4,5,6]. It has been widely accepted by numerous scholars over the last few years that reservoir pores are selfsimilar within a certain range, and this kind of similarity should be resolved into the fractal structure [7, 8]; the fractal. Taking the tight carbonate reservoirs of the Deng-4 member in the central Sichuan basin as an example, in this study, we analyzed the correlations among the porosity, permeability, permeability contribution, and fractal dimension of pores at different scales, which were calculated based on fractal theory and data from experiments with casting thin sections, scanning electron microscopy, and high-pressure Hg injection to provide a theoretical basis for the exploration and development of tight carbonate gas reservoirs

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