Characteristics of Micropore-Throat Structures in Tight Oil Reservoirs: A Case Study of the Jiufotang Formation in the Houhe Region, NE China

Abstract

In order to examine further the characteristics of micropore-throat structures of the tight oil reservoir in the Jiufotang Formation in the Houhe region, this study used whole rock X-ray diffraction, routine physical property analysis, and routine thin section observations to analyze the material composition and physical properties of the tight oil reservoir. CT scanning, high-pressure mercury infiltration, and other test methods were employed to analyze the characteristics of the pore-throat structures in the tight oil reservoir. In addition, the Pearson correlation coefficients quantified the relationships between nine parameters and pore-throat structures. The parameters with high correlations were optimized for analysis, and a comprehensive classification scheme for micropore-throat structures in the tight oil reservoir in the study area was established. The results show that the reservoir in the Jiufotang Formation in the Houhe region is composed of feldspathic and lithic arkosic sandstone, with feldspar and clast pore dissolution pores as the main type of reservoir pore space. The tight oil reservoir has small pore-throat radius, complex structures, poor connectivity, and high heterogeneity. It generally contains micron-sized pores with submicron to nanometer throat widths and small- and medium-sized pores to fine micropore-throat structures. Porosity, permeability, coefficient of variation, skewness coefficient, and average pore-throat radius, were selected for k-means cluster analysis. The micropore-throat structures of the tight oil reservoir were divided into three categories: classes I, II, and III. The study area is dominated by class II pore throats, accounting for 58%. Diagenesis mainly controls the pore-throat structure. These results provide an effective reference for the identification and evaluation of favorable sweet spots in tight oil reservoirs in similar blocks in China.