Study on the Minimum Flow Pore Throat Radius and the Lower Limit of Petrophysical Properties of a Reservoir Under Three Seepage States

The tight sandstone gas in the Xujiahe Formation of the Sichuan Basin offers substantial resources and strong exploration potential. However, identifying desirable reservoirs proves difficult due to factors such as low porosity and permeability, high heterogeneity, and the complex layering of sand bodies. To pinpoint the main factors influencing optimal zones in the tight sandstone reservoir of the fourth member, we systematically analyzed its petrology, physical properties, pore structure, and diagenesis. Our analysis shows that the primary rock type in the target layer is feldspar lithic sandstone, which has generally poor physical properties. The average porosity measures 6.62%, and the average permeability is 0.1495 × 10−3 m, categorizing it as an ultralow porosity and ultralow permeability reservoir. The lower limit of porosity is 6% and the lower limit of permeability is 0.1 × 10−3 m2. We classify the reservoir into two types based on a porosity threshold of 8% and a permeability threshold of 0.3 × 10−3 m. Type I reservoirs show relatively good physical properties, with their reservoir space mainly comprising large pores and high fluid mobility. Reservoir quality depends on both sedimentation and diagenesis, and the physical properties of delta front sand bodies exceed those of delta plain sand bodies. Compaction primarily affects reservoir density, followed by calcite and illite cementation. Additionally, the chlorite rim effectively preserves pores. Secondary dissolution pores formed by feldspar dissolution significantly enhance reservoir space, improving overall reservoir quality.

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Research on the influence of dynamic contact angle of mercury meniscus on the interpretation of rock pore throat radius in mercury intrusion experiments

Dai,

Pi,

et al. 2024

Front. Earth Sci.

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Addressing the lack of measurement methods for dynamic contact angles of mercury meniscus in mercury intrusion porosimetry experiments and the unclear understanding of the impact of dynamic contact angles on the interpretation of pore throat radius in rocks, a new type of closed mercury intrusion characteristic curve (O-R curve) is constructed utilizing the withdrawal curve O and the secondary injection curve R obtained from the experiments. Based on the excellent wetting and de-wetting correlation characteristics at the equal mercury saturation points on this curve, a method for measuring the dynamic contact angles of mercury meniscus (O-R loop method) is established. Taking the Chang 63 tight oil reservoir samples from the Nanliang Oilfield in the Ordos Basin of China as an example, this method is applied to investigate the dynamic contact angles of mercury meniscus in mercury intrusion porosimetry experiments and the impact on the interpretation of pore throat radius in rocks. The results indicate that the dynamic contact angles of mercury meniscus changes significantly during the experiments, which cannot be ignored. And the smaller pore throats lead to more severe deformation of mercury meniscus, resulting in higher wetting resistance coefficients and hysteresis angles. Calculations reveal that the pore throat radius interpreted using the modified Washburn equation (which adopts dynamic contact angles) are generally larger than those interpreted using the conventional Washburn equation (which adopts static contact angles), with relative errors ranging from 12.2% to 54.7%. The smaller the pore throats, the larger the relative errors. The analysis shows that the conventional Washburn equation significantly underestimates the reservoir pore throat radius due to the neglect of the dynamic contact angle, while the modified Washburn equation provides more accurate interpretation. Overall, this research provides a method for calculating the dynamic contact angle in mercury intrusion porosimetry experiments and has important reference significance for the accurate interpretation of rock pore throat radius.

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Study on the Minimum Flow Pore Throat Radius and the Lower Limit of Petrophysical Properties of a Reservoir Under Three Seepage States

Cited by 3 publications

References 1 publication

Water film thickness of tight reservoir in Fuyu oil layer of Cretaceous Quantou Formation in Songliao Basin and its influence on the lower limit of seepage

Water film thickness of tight reservoir in Fuyu oil layer of Cretaceous Quantou Formation in Songliao Basin and its influence on the lower limit of seepage

The classification evaluation of tight sandstone reservoir and the controlling factors of dessert reservoir in the fourth member of Xujiahe Formation in Tianfu area, central Sichuan Basin, China

Research on the influence of dynamic contact angle of mercury meniscus on the interpretation of rock pore throat radius in mercury intrusion experiments

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