Characterization of Closed Pores in Longmaxi Shale by Synchrotron Small-Angle X-ray Scattering

Shale gas/oil remaining in blind pores accounts for a large proportion in total reserves, which is urgent to be further exploited. Understanding the microscopic mechanism of gas/oil extraction from blind pores is critical to enhanced gas/oil recovery. In this study, we investigated the migration and recovery behavior of shale gas/oil mixture through a pore throat connecting blind pores and microfractures. Our simulations show that some oil molecules tend to migrate in the form of clusters, which increases their effective size and causes possible blockage of the pore throat. The recovery ratio of gas/ oil mixture has a strong dependence on the pore size. Below the critical size, which is smaller than the size of oil clusters, the pore throat would be blocked and the recovery ratio will decrease significantly. The heavy fractions of shale oil suppress the extraction of gas/oil molecules from blind pores by four inhibition mechanisms: edge adsorption, surface adsorption, throat blockage, and liquid bridge. The kerogen pore shows a stronger adsorption ability for gas/oil mixture than quartz pore, resulting in more residues in it. We also found that a higher gas/oil ratio can provide a larger driven force, leading to a higher recovery of methane and light fractions. These findings advance the understanding of the recovery mechanisms of remaining gas/oil in blind pores and provide a practical guideline on shale gas/oil exploitation.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Molecular Understanding on Migration and Recovery of Shale Gas/Oil Mixture through a Pore Throat

Hong

et al. 2022

“…Up till now, physical methods to estimate pore structural parameters of shales include molecular probe adsorption (MPA) such as carbon dioxide (CO 2 ) adsorption and N 2 adsorption and desorption, mercury intrusion porosimetry (MIP), the synchrotron small-angle X-ray scattering method (SAXS), and nuclear magnetic resonance (NMR) . In our study, the micropore parameters of the sample were determined via CO 2 adsorption because of its strong accessibility to ultramicropores and micropores. , It was conducted using an ASAP 2020 adsorption analyzer (Micromeritics).…”

Section: Methodsmentioning

confidence: 99%

Methane Adsorption and Desorption on a Deep Shale Matrix under Simulative Reservoir Temperature and Pressure

Cai

Zhang

2022

Further insight into the adsorption and desorption behaviors of methane (CH 4 ) on a shale matrix is critical to shale gas exploration and production. As for the Lower Silurian Longmaxi Formation shale in the Jiaoshiba block, the Sichuan Basin of China, shale gas reserves always occur in reservoirs with burial depths above 3800−4000 m. Thus, the CH 4 adsorption and desorption capability on a deep shale matrix was measured under simulative reservoir temperatures of up to 353.15 K and pressures up to 30.00 MPa. Furthermore, the adsorption mechanism of the CH 4 −shale system was quantitatively elaborated. Finally, the Polanyi potential theory approach was adopted to further clarify CH 4 adsorption and desorption on a deep shale matrix. Results indicated that increasing temperature decreases the CH 4 adsorption capacity of a deep shale matrix. Particularly, its decreasing amplitude reaches up to 20.23% with the temperature increasing from 313.15 to 353.15 K. The adsorption and desorption hystereses of CH 4 on a deep shale matrix were found for all of the operating temperatures. Particularly, the increase in temperature weakens the degree of hysteresis, implying that technologies based on temperature increase could be the future direction of research and development on shale gas production. The weakening temperature dependence of hysteresis is because of the additional energy supplied for desorption and weakened shale matrix swelling due to the high operating temperature. Quantitative analyses indicated that CH 4 adsorption on a deep shale matrix under simulative reservoir temperature and pressure typically follows the micropore-filling mechanism. Accordingly, the Polanyi potential theory is applicable to address the CH 4 −shale adsorption and desorption systems. Moreover, the characteristic curves of both adsorption and desorption of CH 4 on a deep shale matrix show good coincidence for all of the operating temperatures. Thus, the characteristic curve is an effective tool to predict the adsorption and desorption isotherms of CH 4 on a shale matrix at a given temperature and pressure.

“…Ning et al proposed that the difference in the pore size distribution of MIP (reflection of connected pores) and single-phase-fluid saturated NMR T 2 spectrum (reflection of total pores) can indicate the distribution of the nonconnected pores. 68 Similarly, Zhang et al 65 and Wang et al 149 attributed the difference in PSD obtained from MIP (connected pores) and SAXS/SANS (total pores) to the existence of the nonconnected porosity and calculated the proportion of these pores. The above two studies indirectly indicate the structure of nonconnected pores by comparing the differences in the pore structural information that can be measured by different methods.…”

Section: Challenges and Perspectivesmentioning

confidence: 99%

Advances in Microscopic Pore Structure Characterization of Fine-Grained Mudrocks

Wang

Cheng

2023

The microscopic structure of the pore system in fine-grained mudrocks provides spaces for hydrocarbon percolation, migration, and occurrence. It exhibits strong heterogeneity due to the intimate mingling of organic matter (OM) and inorganic minerals and the intricate architecture of the internal network and dynamic changes along the diagenetic pathway and OM thermal maturation. The present review critically summarizes the advances in structure characterization, geological controlling factors, and heterogeneity of the pore system in mudrocks. The pore system in mudrocks can be divided into micro-, meso-, and macropores by diameters, OM-hosted, interparticles, and intraparticle pores by origin and distribution and connected and nonconnected pores according to whether they are connected. The commonly used pore structure characterization techniques can be classified into three categories: i.e., imaging, fluid invasion, and ray-related techniques. Their principles, experimental conditions, applicability, required sample sizes, detectable pore types and diameter ranges, advantages, and disadvantages have been comparatively summarized. To obtain more precise and comprehensive structural properties, multiple techniques are highly recommended to validate and complement each other. The depositional environment, diagenetic events, and OM thermal maturation jointly control the formation and evolution of the pore system. Differences in provenance and depositional background affect primary grain assemblages and thus changes in physical properties during burial depth. Diagenetic transformations mainly change the morphology and structure of mineral-related pores, while OM thermal maturation mainly controls that of OM-hosted pores. Furthermore, the pore structure of mudrocks generally shows strong heterogeneity, which can be effectively assessed by a point-counting porosity quantification and multifractal theory. Finally, we propose the challenges and prospects of microscopic pore structure characterization of mudrocks. More attention needs to be paid to quantifying OM-hosted and mineral-related pore volume fractions, effectively distinguishing connected and nonconnected pores, and comprehensively quantifying the coupled effect of diagenesis and hydrocarbon generation on pore network evolution. In conclusion, the most important aspect of this review is to summarize modern characterization methods and geological controls on pore structure development and propose prospects for unconventional reservoir characterization, with the hope of providing the ultimate knowledge to researchers engaged in unconventional shale oil and gas resources.