Effect of microscopic pore structures on ultrasonic velocity in tight sandstone with different fluid saturation

Xie, Jianyong; Zhang, Junjie; Wang, Xiang; Fang, Yan-Ping; Xue, Yongqiang; Cao, Junxing; Tian, Ren-Fei

doi:10.1016/j.petsci.2022.06.009

Cited by 10 publications

(4 citation statements)

References 33 publications

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“…The P‐wave velocity‐saturation ( V P − S w ) relationship measured in this study, which shows that velocity decreases first and increases with water saturation, differs from those reported in literature. Some measurements indicate that V P increases with S w at oil‐water saturation tests (e.g., Ba et al., 2017; El‐Husseiny et al., 2019) while other studies show that V P at oil or partially oil‐saturated conditions is larger than that saturated with water (e.g., Pei et al., 2011; Xie et al., 2022). In our measurements, V P decreases until S w reaches 40% or 60%.…”

Section: Discussionmentioning

confidence: 99%

Effects of Pore Geometry and Saturation on the Behavior of Multiscale Waves in Tight Sandstone Layers

Ba,

Ma,

Carcione

et al. 2023

JGR Solid Earth

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Geometric heterogeneities in tight reservoir rocks saturated with a fluid mixture may exhibit different scale distribution characteristics. Conventional models of rock physics based on poroelasticity, which usually consider single‐scale pore structure and fluid patches, are inadequate for describing elastic wave responses. A major challenge is to establish the relationship between the wave response at different spatial scales and frequencies. To address this problem, three sets of observational data over a wide frequency range were obtained from a tight oil reservoir in the Ordos Basin, China. Ultrasonic measurements were made on eight sandstone samples at partial oil‐water saturation at 0.55 MHz. Data from six borehole measurements and seismic profiles were acquired and analyzed at about 10 kHz and 30 Hz, respectively. Analysis of the cast thin sections shows that dissolution pores and microcracks generally develop, with fractal dimensions of the pores ranging from 2.45 to 2.67 for the samples with porosities between 5.1% and 10.2%. Compressional wave velocity and attenuation were estimated from the observed data. The results show that the velocity dispersion from seismic to ultrasonic frequencies is 10.02%, mostly occurring between sonic and ultrasonic frequencies. The attenuation is stronger at higher oil saturation. The relationships between velocity, attenuation, and wavelength were established and can be used for further forward modeling and seismic interpretation studies. A partial saturation model has been derived based on effective differential medium theory and a double double‐porosity model, assuming that the medium contains fractal cracks and fluid patches. The effects of scale and saturation on wave responses are prevalent. Modeling results consistent with observed data show that the radii of cracks and fluid patches range from 0.1 μm to 2.8 mm, affecting ultrasonic, acoustic, and seismic attenuation. The multiscale data and proposed model quantify the relationship between fracture and fluid distributions and attenuation and could be useful for upscaling to the reservoir scale. The study helps improve the understanding of seismic wave propagation in partially saturated rocks, which has potential applications in seismic exploration, hydrocarbon production in reservoirs, and CO2 sequestration in aquifers.

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Section: Discussionmentioning

confidence: 99%

Effects of Pore Geometry and Saturation on the Behavior of Multiscale Waves in Tight Sandstone Layers

Ba,

Ma,

Carcione

et al. 2023

JGR Solid Earth

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“…The distribution characteristics of pores and throats in reservoirs were determined by the composition of rocks and the arrangement and sorting of particles. The casting thin section could effectively show the granularity, connectedness, distribution, and combination characterization of the samples [29].…”

Section: Casting Thin Sectionmentioning

confidence: 99%

Pore- and Core-Scale Recovery Performance of Consortium Bacteria from Low-Permeability Reservoir

Bian,

Song,

Zhi

et al. 2023

Microorganisms

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Performance evaluation of microorganisms that have emulsifying and degrading effects on crude oil has been extensively conducted in the laboratory. However, the ultimate goal of microbial enhanced oil recovery is field application, so the pilot simulation experiments are crucial. In this study, a micro-visualization model and the real cores were chosen to investigate the actual recovery efficiency and the mechanism of the consortium bacteria B-ALL, which has been proven to have good emulsification and degradation effects in lab studies in porous media. At the same time, the cast thin sections and rate-controlled porosimetry were combined to analyze the pore throat structure of the displacement core. It was found that the recovery efficiency was positively correlated with the microbial injection volume as well as the incubation time. For the microscopic model with high pores and high permeability, the efficiency of secondary water flooding can be increased by 44.77% after six days of incubation with two pore volume microbes. For the real tight cores, the maximum secondary water flooding efficiency under the same condition was 6.98%. Through visual modeling, microorganisms increase the oil washing efficiency mainly by emulsification and changing the wettability. The generated oil droplets will play a role in plugging and improving the wave efficiency. However, tight reservoirs have the characteristics of large pores and small throats, and curved and necking throats are developed, greatly reducing permeability. The microbial recovery efficiency was lower under shorter cultivation times. This study provides a practical basis for the application of consortium bacteria in tight oil fields to enhance recovery.

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“…Many researchers define reservoirs with porosity of less than 10% and permeability of less than 0.1 mD as tight sandstone reservoirs [11,12]. A microscopic pore-throat structure refers to characteristics such as the pore-throat size, geometric shape, and connectivity [13,14]. These characteristics play a pivotal role in determining the reservoir's porosity and permeability and at the macroscopic level control the storage and transport of oil and gas [13,15].…”

Section: Introductionmentioning

confidence: 99%

“…A microscopic pore-throat structure refers to characteristics such as the pore-throat size, geometric shape, and connectivity [13,14]. These characteristics play a pivotal role in determining the reservoir's porosity and permeability and at the macroscopic level control the storage and transport of oil and gas [13,15]. Tight sandstone is characterized by fine pores and complex microscopic pore-throat structures, poor pore connectivity, and high heterogeneity, primarily distributed in the nanometer to micrometer range [10,16,17].…”

Section: Introductionmentioning

confidence: 99%

Fractal Characterization of the Pore-Throat Structure in Tight Sandstone Based on Low-Temperature Nitrogen Gas Adsorption and High-Pressure Mercury Injection

He,

Zhou,

Chen

et al. 2024

Fractal Fract

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The pore-throat structure is a critical factor in the study of unconventional oil and gas reservoirs, drawing particular attention from petroleum geologists, and it is of paramount significance to analyze to enhance oil and gas production. In tight sandstone, which serves as a significant hydrocarbon reservoir, the internal pore-throat structure plays a decisive role in the storage and migration of fluids such as water, gases, and hydrocarbons. This paper employs casting thin section (CTS), field emission scanning electron microscope (FE-SEM), high-pressure mercury injection (HPMI), and low-temperature nitrogen gas adsorption (LT−N2−GA) experimental tests to qualitatively and quantitatively analyze the characteristics of the pore-throat structure in tight sandstone. The results indicate that the pore types in tight sandstone include intergranular residual pores, dissolution pores, intercrystalline pores, and microfractures, while the throat types encompass sheet-shaped, curved-sheet-shaped, and tubular throats. Analysis of the physical and structural parameters from 13 HPMI and 5 LT−N2−GA samples reveals a bimodal distribution of pore-throat radii. The complexity of the pore-throat structure is identified as a primary controlling factor for reservoir permeability. The fractal dimension (D) exhibits an average value of 2.45, displaying a negative correlation with porosity (R2 = 0.22), permeability (R2 = 0.65), the pore-throat diameter (R2 = 0.58), and maximum mercury saturation (R2 = 0.86) and a positive correlation with threshold pressure (R2 = 0.56), median saturation pressure (R2 = 0.49), BET specific surface area (R2 = 0.51), and BJH total pore volume (R2 = 0.14). As D increases, reservoir pores tend to decrease in size, leading to reduced flow and deteriorated physical properties, indicative of a more complex pore-throat structure.

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Effect of microscopic pore structures on ultrasonic velocity in tight sandstone with different fluid saturation

Cited by 10 publications

References 33 publications

Effects of Pore Geometry and Saturation on the Behavior of Multiscale Waves in Tight Sandstone Layers

Effects of Pore Geometry and Saturation on the Behavior of Multiscale Waves in Tight Sandstone Layers

Pore- and Core-Scale Recovery Performance of Consortium Bacteria from Low-Permeability Reservoir

Fractal Characterization of the Pore-Throat Structure in Tight Sandstone Based on Low-Temperature Nitrogen Gas Adsorption and High-Pressure Mercury Injection

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