AUTHOR=Tian Kun , Qiao Xiangyang , Zhou Jinsong , Xue Chunqi , Cao Jun , Yin Xiao , Lv Shuo , Zhugeng Bolun 

TITLE=Pore structure characteristics and influencing factors of dolomite reservoirs: a case study of the lower Ordovician Majiagou Formation, Ordos Basin, China

JOURNAL=Frontiers in Earth Science

VOLUME=Volume 12 - 2024

YEAR=2024

URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2024.1407967

DOI=10.3389/feart.2024.1407967

ISSN=2296-6463

ABSTRACT=The evaluation of the pore structure in dolomite, particularly with regard to pore heterogeneity, geometry and connectivity, is crucial for oil and gas field production and reservoir prediction. The subsalt dolomite reservoir in the Ordovician strata of the Ordos Basin has shown promising exploration results and is anticipated to have a high hydrocarbon potential. However, there has been limited research on pore structure and primary controlling factors of Ordovician Majiagou reservoir in the south-central Ordos Basin. Therefore, we conducted a comprehensive analysis of the pore structure and fractal characteristics using routine petrophysical measurements, thin section analysis and high pressure mercury injection (HPMI) data. We also discussed the relationship between fractal dimension and reservoir physical properties as well as pore structure, along with exploring the origin of potentially prolific reservoirs. Our observations from thin section identified four main pore types: intercrystalline pores, intercrystalline dissolved pores, dissolved pores and micro-fracture. The data from HPMI revealed that the average pore-throat radii range from 0.009μm to 0.015μm with porosity ranging from 0.4% to 5.26%, and permeability ranging from 0.011mD to 0.059mD. There were further categorized into three reservoir types: dissolved pore type, intra-crystalline (dissolved) pore type, and micro-porous type. The fractal dimension was calculated based on HPMI data, and the reservoir's fractal characteristics were divided into two segments. The dissolved pore type was identified as potentially prolific reservoir due to its larger pore size and volume, moderate permeability, and homogeneity on pore structure.