Pore and throat characterization of tight reservoirs based on the methods of alloy injection and large-field image stitching

Abstract

Tight oil and gas is an important part of China's oil and gas resources, and the study of related pore-throat structure is conducive to the enrichment and improvement of tight oil and gas geological theory. Taking the tight reservoir of the Triassic Yanchang Formation in the Ordos Basin as an example, combined with large-field image stitching method and image pore extraction method, this paper established a new method for pore-throat structure characterization of tight reservoir with high-temperature and high-pressure alloy injection. Results show that the alloy injected into the pores of tight reservoirs can reflect the characteristics of pore connectivity better, and the pore morphology and structure are easier to be identified. The large-field image stitching method solves the problem of strong heterogeneity of pore distribution and poor representativeness of small-field observation. The tight reservoirs of the Yanchang Formation in the Ordos Basin are mainly composed of intergranular pores, intragranular pores, and intergranular-intragranular mixed pores, among which the intergranular pores are mostly developed. There are five types of throats, including pore shrinkage throat, neck constricted throat, bundle throat, sheet throat and curved sheet throat, among which the curved sheet throat is mostly developed. The porosity of quartz and feldspar is significantly larger than that of other minerals, contributing 74% to the surface porosity of tight reservoir, and is an important occurring space for tight oil and gas.

Keywords

• pore-throat structure
• alloy injection
• large-field image
• pore-throat extraction
• tight reservoir