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DOI: https://doi.org/10.11698/PED.20250416

Dynamic evolution mechanism of petrophysical properties in shale reservoirs and its petroleum geological significance: A case study of the Cretaceous Lower Eagle Ford Formation, Gulf Coast Basin, USA

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  • PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China

Received date: 2025-07-31

  Revised date: 2025-12-11

  Online published: 2026-03-24

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Abstract

Utilizing test data, production performance data, logging data and seismic data of shale samples from the Cretaceous Lower Eagle Ford Formation in the Gulf Coast Basin, USA, this study analyzes average values across varying intervals of original total organic carbon, vitrinite reflectance, and clay mineral content to propose methods for determining organic and inorganic matrix porosity and reconstructing the original total organic carbon. The results demonstrate that shale matrix porosity is primarily controlled by the original total organic carbon and vitrinite reflectance, with organic pores contributing up to 68% to porosity evolution, while inorganic matrix porosity remains relatively stable, exhibiting a minor reduction of approximately 0.62 percentage points due to clay mineral transformation. As the vitrinite reflectance increases, matrix porosity exhibits a trend of initial increase, subsequent decrease, and a secondary increase before ultimately stabilizing; meanwhile, effective matrix porosity increases with thermal maturity, with the ratio of effective-to-total matrix porosity rising from approximately 53% in low-maturity stages to 79% in high-maturity stages. Additionally, a strong positive correlation is found between water-filled matrix porosity and clay mineral content, between matrix permeability and matrix porosity, and between vertical and horizontal permeability. Fracture porosity is predominantly controlled by the intensity of tectonic activity, and estimated ultimate recovery is primarily governed by hydrocarbon-filled matrix porosity and fracture porosity. By establishing evaluation models for matrix porosity, fracture porosity, and permeability, this study reveals the dynamic evolution mechanisms of reservoir properties throughout the entire thermal maturation of shale, characterized by pore generation and permeability enhancement via organic hydrocarbon generation, porosity-permeability enhancement through tectonic fracturing, porosity reduction due to oil cracking and subsequent pore-filling by pyrobitumen/bitumen, and porosity reduction driven by clay mineral transformation.

Key words： shale oil and gas; reservoir physical properties; organic matrix porosity; fracture porosity; clay mineral content; estimated ultimate recovery; Cretaceous Eagle Ford Formation; Gulf Coast Basin

Cite this article

HOU Lianhua, ZHAO Zhongying, WU Songtao, HOU Mingqiu, WANG Zhaoming, LIN Senhu, YANG Zhi, LI Siyang, ZHANG Mengyao, LUO Xia . Dynamic evolution mechanism of petrophysical properties in shale reservoirs and its petroleum geological significance: A case study of the Cretaceous Lower Eagle Ford Formation, Gulf Coast Basin, USA[J]. Petroleum Exploration and Development, 0 : 20260230 -20260230 . DOI: 10.11698/PED.20250416

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