Microscopic pore structure characteristics and genesis of coal-measure tight sandstone reservoirs in Longtan Formation of Qianxi Area

doi:10.3969/j.issn.1006-6535.2026.02.005

Abstract

Abstract: Tight sandstone gas exploration in the Qianxi Area is still at the preliminary stage,and no large scale tight gas reservoir has been found so far.Given the insufficient understanding of the pore structure and genesis of the coal-measure tight sandstone reservoirs of Longtan Formation in this area,thin section analysis,X-ray diffraction,scanning electron microscopy(SEM),high pressure mercury intrusion,and negative pressure porosity-permeability experiments were conducted to systematically investigate the pore structure,porosity-permeability relationships,brittleness characteristics,and the effects of diagenesis and tectonism on reservoir development.The results show that Longtan Formation sandstones in Qianxi Area are typical tight sandstone,with an average porosity of 4.14% and an average permeability of 0.032 8 mD,corresponding to ultra-low porosity and ultra-low permeability reservoirs.Pore types are mainly primary pores,secondary pores,organic-matter pores, and microfractures.Secondary pores consist predominantly of intragranular dissolution pores and intergranular dissolution pores,and microfractures account for up to 35%,greatly influencing reservoir storage and permeability.Reservoir development is controlled by both diagenetic and tectonic processes:compaction is intense and cementation is significant,whereas microfractures formed by tectonic activity play a decisive role in reservoir performance.The upper member sandstones of Longtan Formation exhibit better reservoir properties than the lower member,and tight sandstones from deltaic deposits exhibit better reservoir properties than those from lagoon-tidal flat deposits.This study provides important guidance for the exploration and development of coal-measure tight gas in this area.

Key words: Qianxi Area, Longtan Formation, coal-measure tight sandstone, pore structure, genetic mechanism

CLC Number:

TE122.2

HUANG Zhengxin, ZHANG Xiaoli, YANG Zhaobiao, HE Jinxian, WU Meng, CAO Wenjie, LI Juhao. Microscopic pore structure characteristics and genesis of coal-measure tight sandstone reservoirs in Longtan Formation of Qianxi Area[J]. Special Oil & Gas Reservoirs, 2026, 33(2): 44-53.

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