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Numerical modeling of micro-particle migration in channels
Get PDFPhysicochemical forces exert non-neligible effects on the migration of micro-particles in channels. Experiments, analytical and non-resolved computational fluid dynamics models have failed to decipher the dynamic behaviors of these particles when carried by fluid flow. In this paper, particle-scale numerical simulation is conducted to study the adhesive micro-particle migration process during duct flow in channels with a large characteristic dimension ratio and those with relatively small such ratio based on the coupled lattice Boltzmann method-discrete element method. The interaction between particle and fluid flow is dealt with by the immersed moving boundary condition. For micro-particle migration in duct flow, the effects of hydrodynamic force, adhesive force and particle concentration on the aggregation of particles are investigated. Based on the concept of hydrodynamic and adhesive force ratio, a stable aggregation distribution map is proposed to help analyze the distribution and size of the formed agglomerates. For micro-particle migration in channels with small characteristic dimension ratio, the general particle migration process is analyzed, which includes single particle retention, followed by particle capture, and the migration of large agglomerates. It is concluded that two factors accelerate single particle retention in a curved channel. Moreover, it is established that higher fluid flow rate facilitates the formation of large and compact agglomerate, and blockage by this can cause severe damage to the conductivity of the channel.Document Type: Original articleCited as: Wang, D., Qian, Q., Zhong, A., Lu, M., Zhang, Z. Numerical modeling of micro-particle migration in channels. Advances in Geo-Energy Research, 2023, 10(2): 117-132. https://doi.org/10.46690/ager.2023.11.0
Wettability controlling effects on the fluid occurrence and flow in shale gas reservoirs: Present problems and new sights
Get PDFThe wettability of shale is critical for the development of shale oil and gas reservoirs. Due to its complex composition, which includes organic materials and a number of different inorganic minerals, shale’s wettability may show high heterogeneity. This could significantly affect fluid occurrence and flow processes in various kinds of pores. Organic and inorganic pores may have varying capillary pressures. The methodologies to describe the capillary forces in these two varieties of pores are still lacking, though. Additionally, due to the strong capillary pressure that may prevent liquid water from entering organic pores, the mechanisms by which water and methane accumulate in inorganic pores and organic pores may differ. Therefore, the two-phase occurrence mechanisms in the various types of pores in shale continue to be difficult problems. Furthermore, because organic and inorganic pores differ in their capillary pressure and fluid occurrence, wettability can have a significant effect on relative permeability. Thus, wettability is a significant factor that impacts the exploration and development of shale gas reservoirs. The development of shale gas reservoirs could benefit significantly from a thorough understanding of wettability heterogeneity, capillary pressure, water-methane occurrence, and relative permeability.Document Type: Current minireviewCited as: Zhang, S., Wang, T., Gao, Z., Zhang, Y. Wettability controlling effects on the fluid occurrence and flow in shale gas reservoirs: Present problems and new sights. Capillarity, 2023, 9(2): 25-31. https://doi.org/10.46690/capi.2023.11.0
Effects of fracturing fluid composition and other factors on improving the oil imbibition recovery of shale reservoir
Get PDFImbibition is an important mechanism of shale reservoir development. In exploring the factors affecting the enhanced recovery of shale reservoirs by imbibition, laboratory spontaneous and forced imbibition experiments were conducted using outcrop cores of shale reservoirs. The effects of imbibition agent composition, fracture, and pressure on imbibition are obtained in this work based on imbibition recovery test findings and imbibition theory. Results show that the imbibition curve includes three stages, namely, imbibition, transition, and stability. Among the components of compound fracking fluid, surfactants have the greatest impact, whereas emulsifiers have the least impact. Complex crack structures and high-temperature environments can improve imbibition recovery. Pressure is inversely proportional to imbibition recovery in the highly stress-sensitive shale reservoir. In addition, the throughput time of the imbibition agent has an optimal value in the shale reservoir. After the huff-n-puff time exceeds the optimal value, the imbibition agent should be replaced to continuously improve the imbibition effect. The research results can serve as a basis for enhancing oil recovery through imbibition.Document Type: Original articleCited as: Li, S., Ye, Z., Wang, J., Tang, L., Lai, N. Effects of fracturing fluid composition and other factors on improving the oil imbibition recovery of shale reservoir. Capillarity, 2023, 9(3): 45-54. https://doi.org/10.46690/capi.2023.12.0
CO2 capillary trapping in layered sandstone dominated by inertial force and gravity
Get PDFCapillary trapping is an important strategy to prevent CO2 from escaping. Meanwhile, under immiscible conditions, CO2 may travel upwards by gravity. Studying the long-term effects of gravity and layered heterogeneity on CO2 transport is crucial for ensuring CO2 storage security in aquifers. In this work, fluid flow experiments driven by inertial force and gravity are conducted in a specially constructed layered sandstone. Whether driven by inertial force or gravity, the variation in CO2 distribution in the high-permeability layer is consistently the most significant factor. In the low-permeability layer, the saturation and capillary pressure distribution of CO2 clusters vary less and the geometric shapes are also more complex, thus the CO2 capillary trapping in this layer is more stable. This work demonstrates that the low-permeability layer can effectively prevent CO2 from escaping upwards when the permeability ratio between layers approaches two.Document Type: Short communicationCited as: Li, Y., Yang, Y., Dong, M. CO2 capillary trapping in layered sandstone dominated by inertial force and gravity. Capillarity, 2024, 10(1): 22-28. https://doi.org/10.46690/capi.2024.01.0
Quantitative characterization of fluid occurrence in shale reservoirs
Get PDFShale oil and gas, as important unconventional resources, have been widely discussed in the last decade. The occurrence characteristics of fluids (oil, gas, and water) in shale reservoirs are closely related to the exploitation of shale oil and gas, therefore the quantitative characterization of fluid occurrence in shale reservoirs has received extensive attention. In this paper, the latest advances and potential challenges on this subject are summarized. With respect to shale oil, the amounts, ratios and micro-distributions of shale oil in different states can be determined using the state equation of liquid and adsorption ratio equation, which contributes to identifying high-quality shale oil reservoirs. However, it is still necessary to strengthen the research on the multi-attribute coupling relationship and oil-rock interaction of shale oil reservoirs, and the determination of occurrence characteristics of adsorbed and free oil under in situ reservoir conditions. In terms of shale gas evaluation, the process analysis method and isotope fractionation method effectively solve the problem of evaluating in situ gas-bearing characteristics of shale, and can accurately estimate the amounts of total, adsorbed and free gas. The quantum physisorption behavior of gas could be a new research direction to reveal the microscopic occurrence mechanism of shale gas. As for shale pore water, a complete evaluation procedure for determining the amounts and micro-distributions of adsorbed and free water in shale matrix pores has been established, which provides insight into the storage and flow of oil and gas. In future work, a study on the quantitative evaluation of water-rock interaction is significant for obtaining the adsorbed and free water under in situ reservoir conditions.Document Type: PerspectiveCited as: Li, J., Cai, J. Quantitative characterization of fluid occurrence in shale reservoirs. Advances in Geo-Energy Research, 2023, 9(3): 146-151. https://doi.org/10.46690/ager.2023.09.0
Recent research progress on imbibition system of nanoparticle-surfactant dispersions
Get PDFNanotechnology has been increasingly applied in the petroleum industry in recent years. In particular, dispersions consisting of nanoparticles and surfactants have been widely investigated. The imbibition system compounded by nanoparticle and surfactant was found to display a high efficiency in enhancing oil recovery. This paper briefly reviews the factors influencing imbibition efficiency. At the same time, the application and mechanism of the imbibition system of nanoparticle-surfactant dispersion in the field of enhanced oil recovery are introduced. Additionally, the limitations and challenges that the imbibition system of nanoparticle-surfactant dispersions may face in enhanced oil recovery applications are put forward. The current work reveals that the imbibition system with nanoparticle-surfactant dispersion is an ideal candidate for enhanced oil recovery in tight and low-permeability reservoirs.Document Type: Invited reviewCited as: Shao, W., Yang, J., Wang, H., Chang, J., Wu, H., Hou, J. Recent research progress on imbibition system of nanoparticle-surfactant dispersions. Capillarity, 2023, 8(2): 34-44. https://doi.org/10.46690/capi.2023.08.0
Advances in the application of deep learning methods to digital rock technology
Get PDFDigital rock technology is becoming essential in reservoir engineering and petrophysics. Three-dimensional digital rock reconstruction, image resolution enhancement, image segmentation, and rock parameters prediction are all crucial steps in enabling the overall analysis of digital rocks to overcome the shortcomings and limitations of traditional methods. Artificial intelligence technology, which has started to play a significant role in many different fields, may provide a new direction for the development of digital rock technology. This work presents a systematic review of the deep learning methods that are being applied to tasks within digital rock analysis, including the reconstruction of digital rocks, high-resolution image acquisition, grayscale image segmentation, and parameter prediction. The results of these applications prove that state-of-the-art deep learning methods can help advance and provide a new approach to scientific knowledge in the field of digital rocks. This work also discusses future research and developments on the application of deep learning methods to digital rock technology.Document Type: Invited reviewCited as: Li, X., Li, B., Liu, F., Li, T., Nie, X. Advances in the application of deep learning methods to digital rock technology. Advances in Geo-Energy Research, 2023, 8(1): 5-18. https://doi.org/10.46690/ager.2023.04.0
Predicting brittleness indices of prospective shale formations from sparse well-log suites assisted by derivative and volatility attributes
Get PDFA technique is proposed that calculates derivative and volatility attributes from just a few well log curves to assist in brittleness index predictions from sparse well-log datasets with machine learning methods. Six well-log attributes are calculated for selected recorded well logs: the first derivative, the moving average of the first derivative, the second derivative, the logarithm of the instantaneous volatility, the standard deviation of volatility, and the moving average of volatility. These attributes make it possible to extrapolate brittleness index calibrations from the few cored and comprehensively logged wells to surrounding wells in which only minimal well-log suites are recorded. Data from two cored wells penetrating the lower Barnett Shale with distinct lithology and five well logs recorded are used to demonstrate the technique. Based on multi-K-fold cross validation analysis, the data matching K-nearest neighbour machine learning model provides the most accurate brittleness index predictions, closely followed by tree-ensemble models. For this dataset, recorded data from three well logs plus calculated attributes matches the brittleness index prediction accuracy that is achieved by the five recorded logs. Moreover, any one of the logs plus their calculated attributes yields better brittleness index prediction performance than that achieved by a combination of just those three recorded well logs. Analysis of the Gini indices of the tree-ensemble models reveals the relative influences of the recorded logs and their attributes on the brittleness index prediction solutions. Such information is used to perform feature selection to optimize the well-log attributes involved to generate reliable brittleness index predictions.Cited as: Wood, D. A. Predicting brittleness indices of prospective shale formations from sparse well-log suites assisted by derivative and volatility attributes. Advances in Geo-Energy Research, 2022, 6(4): 334-346. https://doi.org/10.46690/ager.2022.04.0
The effect of supercritical CO2 on failure mechanisms of hot dry rock
Get PDFHot dry rock is a clean, renewable resource of geothermal energy with good stability and a high utilization rate. Supercritical CO2 has shown promising results for improving the permeability and heat exchange of hot dry rock. In order to demonstrate the effect of supercritical CO2 on the failure mechanism of granite, the acoustic emission of granite during its failure process were studied in addition to X-ray diffraction, scanning electron microscopy, and optical electron microscopy investigations. The experimental results showed that for granite without supercritical CO2 treatment, as it approached failure, there were many acoustic emission events with a waiting time less than 0.0001 s, and that the power law exponent of the acoustic emission energy distribution decreased. The failure mechanisms were a combination of fracture and friction, with fracturing dominant. After immersion in supercritical CO2 , new cracks and pores appeared in the granite due to the dissolution of minerals, but friction was also a factor evidenced in particle crumbing. Generally, the acoustic emission statistical distributions of granite before and after supercritical CO2 soaking conformed to the seismic statistical distribution law. This study is conducive to increasing the understanding of artificial earthquakes induced by the development of hot dry rock.Cited as: Li, H., Jiang, X., Xu, Z., Bowden, S. The effect of supercritical CO2 on failure mechanisms of hot dry rock. Advances in Geo-Energy Research, 2022, 6(4): 324-333. https://doi.org/10.46690/ager.2022.04.0
Experimental investigation on plugging performance of nanospheres in low-permeability reservoir with bottom water
Get PDFThe oil production rate decreases rapidly after a short period of high yield from acidizing or fracturing in low-permeability reservoirs. In this paper, nanospheres are applied before the fracturing step, which possess the ability to absorb water and expand in the water layer, reducing the flow capacity of bottom water and finally enhancing the oil recovery. The plugging performance is investigated by nanosphere displacement experiments in cores and sand-packs, which explores the plugging effect in the oil layer, the oil-water transition zones, the water layer and the fracturing zones. In addition, a nuclear magnetic resonance experiment is conducted to study the flow mechanism of nanospheres and determine the plugging rates, which can characterize the plugging performance of nanospheres in porous media. The results show that the plugging rate is 85.84% and 78.65% on the water layer and oil-water transition zone, respectively, and 94.36% in the fracturing zone. Meanwhile, the nanospheres cannot plug the oil layer. The formation pressure has a less considerable effect on the plugging performance of nanospheres. The nanospheres have good injectivity, and the intensity variations in small, medium and large pores account for 34.46%, 13.22% and 52.32%, respectively. Overall, this paper explores the feasibility of applying nanospheres for water plugging and enhanced oil recovery.Cited as: Tang, M., Wang, C., Deng, X., Yang, H., Lu, J., Yu, H. Experimental investigation on plugging performance of nanospheres in low-permeability reservoir with bottom water. Advances in Geo-Energy Research, 2022, 6(2): 95-103. https://doi.org/10.46690/ager.2022.02.0