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Development and performance evaluation of bioenzyme-responsive temporary plugging materials
Get PDFOcean gas hydrate is a potentially efficient and clean oil and gas alternative energy resource. Wells with complex structure, such as horizontal wells, can improve the extraction efficiency; however, drilling operations face challenges such as wellbore instability and reservoir damage due to the complex interaction between drilling fluids and hydrate reservoirs. This work presents a ceramsite temporary plugging microcapsule that uses ceramsite modified by 3-aminopropyltriethoxysilane as the core material and chitosan and sodium alginate as shell materials. It exhibits high strength during drilling and excellent plugging effects. After the action of bioenzymes, it can easily be dissolved, leading to high permeability post-drilling. The analysis and performance evaluation of ceramsite microcapsules show that their particle size is generally 40 μm, which can match the pore size of the hydrate reservoir depending on the number of encapsulation layers. Bioenzyme optimization at 15 ◦C yields the best permeability recovery of 74.5% for the low-temperature composite enzyme. As the temperature rises, the permeability recovery rate of ceramic microcapsules gradually increases and the difference in permeability recovery rate between 5 and 25 ◦C becomes more significant. With a longer degradation time, the permeability recovery rate of ceramsite microcapsules gradually enhances and the difference in permeability recovery rate becomes smaller after 12 h. The microcapsules exhibit a specific inhibitory effect on the decomposition of hydrates. Utilizing bioenzyme- responsive ceramsite microcapsules as temporary plugging materials can establish an “isolation barrier” around the wellbore, effectively sealing off the interaction between the wellbore and the gas hydrate reservoir during the drilling process. Re-opening the flow path around the well by bio-enzymatic unblocking at the end of drilling proves to be effective in solving the problem of balancing the stability of the well wall and protecting the reservoir.Document Type: Original articleCited as: Sun, J., Li, Y., Liao, B., Bai, Y., Li, W., Wang, J. Development and performance evaluation of bioenzyme-responsive temporary plugging materials. Advances in Geo-Energy Research, 2024, 11(1): 20-28. https://doi.org/10.46690/ager.2024.01.0
Pore-scale numerical simulation of spontaneous imbibition in porous media containing fractures
Get PDFSpontaneous imbibition is an essential mechanism for recovering oil from low-permeability fractured water-driven reservoirs. To accurately capture the migration interface of oil-water two-phase flow under these conditions, this study employs phase field theory coupled with Cahn-Hilliard and Navier-Stokes equations. We conduct a numerical pore-scale investigation on countercurrent imbibition in low-permeability fractured porous media. The results show that pore-scale spontaneous imbibition can be divided into four stages. In the first stage, oil-water film is formed when oil contacts with water, and this contact line moves under the action of capillary force. In the second stage, the oil film at the end of the oil cluster ruptures to form isolated oil droplets. In the third stage, these oil droplets are surrounded by water and gradually transported outward. In the final stage, oil droplets accumulate in the fractures and are collectively expelled from the matrix. In the process of oil droplet migration, the phenomenon of sticking occurs under the influence of water extrusion and the internal structure of the matrix, which leads to the formation of residual oil. The increased complexity of open boundary and fracture development strengthens the imbibition effect by elevating the degree of spontaneous imbibition pore utilization, thus improving the oil utilization efficiency. The above findings can provide a numerical modeling reference for the study of spontaneous imbibition in fractured porous media, and at the same time, has some guiding significance for the development of low-permeability reservoirs.Document Type: Original articleCited as: Yang, L., Jiang, X., Li, M., Gong, F., Dong, G., Li, X. Pore-scale numerical simulation of spontaneous imbibition in porous media containing fractures. Capillarity, 2024, 10(2): 48-56. https://doi.org/10.46690/capi.2024.02.0
Structural evolution and characterization of organic-rich shale from macroscopic to microscopic resolution: The significance of tectonic activity
Get PDFShale gas exploration and development have taken significant strides in the relatively straightforward intra-basin stability zone and intra-basin weak deformation zone of marine shale in the Sichuan Basin, South China. In addition, the extra-basin strong tectonic modification zones have been actively explored. However, the results have been limited, which reveals the complexity of shale gas formation and preservation conditions in the context of multi-scale geological processes. These tectonic geological conditions have a significant impact on the shale gas content, while it has been difficult to figure out how tectonic deformation modifies reservoir structure and what specific mechanism causes shale gas content anomalies. Based on subjecting geologic samples to combined high-temperature and high-pressure experiments, this study summarizes the tectonic constraint mechanism of shale petrophysical structure evolution and its impact on shale gas storage, reveals the intrinsic connection and mechanism of shale pore-fracture and organic matter, inorganic mineral particle structure evolution and tectonic stress, and identifies the remodeling mechanism of the shale reservoir physical property change. The findings contribute to the theory of shale deformation and gas accumulation, as well as offer a scientific foundation for the exploration of marine shale gas in the complex tectonic zones outside the Sichuan Basin.Document Type: PerspectiveCited as: Gao, J., Li, X., Cheng, G., Luo, H., Zhu, H. Structural evolution and characterization of organic-rich shale from macroscopic to microscopic resolution: The significance of tectonic activity. Advances in Geo-Energy Research, 2023, 10(2): 84-90. https://doi.org/10.46690/ager.2023.11.0
Impact of capillary pressure on micro-fracture propagation pressure during hydraulic fracturing in shales: An analytical model
Get PDFThe presence of micro-fractures in shale reservoirs is vital for economic production. While a number of models have been proposed to predict the propagation pressure of pre-existing micro-fractures, few models have considered capillary pressure, which may play a significant role in the presence of micro-fractures with nano-scale width. In this study, a new model was developed to predict the propagation pressure of microfractures. It is assumed that pre-existing micro-fractures are arbitrarily intersected with the propagated hydraulic fractures. The model was derived based upon linear elastic fracture mechanics under the condition of mode I fracture propagation coupled with capillary pressure. Furthermore, this paper also conducted sensitivity analyses to predict the micro-fracture propagation pressure as a function of the contact angle, surface tension and the width of micro-fracture. The results demonstrated that decreasing the contact angle reduces the propagation pressure of micro-fractures, implying that a hydrophilic system may yield a lower fracture propagation pressure compared with the hydrophobic counterpart. Moreover, for a hydrophilic system, further decreasing the contact angle shifts the propagation pressure to a negative value, implying that the capillary pressure may induce the propagation of micro-fractures without external fluid injection. The propagation pressure is also affected by the surface tension and the width of micro-fracture.Document Type: Original articleCited as: Lu, Y., Jin, Y., Li, H. Impact of capillary pressure on micro-fracture propagation pressure during hydraulic fracturing in shales: An analytical model. Capillarity, 2023, 8(3): 45-52. https://doi.org/10.46690/capi.2023.09.0
Construction of PAN-based activated carbon nanofibers for hydrogen storage under ambient pressure
Get PDFAdsorption agents are an important class of solid hydrogen storage materials. Attributed to their high specific surface area and adjustable nanopore structure, activated carbon nanofibers have attracted extensive attention in the application of solid hydrogen storage. The research in this field mostly focuses on applications with a hydrogen pressure condition of 30 to 300 bar, while there have been few systematic studies on the hydrogen storage performance of these materials under ambient pressure. In this study, polyacrylonitrile-based activated carbon nanofibers were constructed by electrospinning technology and ultrasonic-assisted activation technology for the application of atmospheric hydrogen storage. Their nanopore structure was revealed to be mainly composed of micropores, and the relative contents of micropore volume and ultramicropore volume were 77.92% to 88.3% and 22.34% to 24.68%, respectively. Attributed to the synergy of rich microporous structure and surface chemical structure, the atmospheric hydrogen storage density of activated carbon nanofibers could reach 2.64 wt% at 77 K and 1 bar. After the optimization analysis of adsorption isotherm models, the Multisite-Langmuir model was found as more suitable for accurately describing the atmospheric hydrogen adsorption process of activated carbon nanofibers.Document Type: Original articleCited as: Yu, J., Lin, T., Li, J., Zhang, W., Bao, W., Zhu, B. Construction of PAN-based activated carbon nanofibers for hydrogen storage under ambient pressure. Capillarity, 2023, 6(3): 49-56. https://doi.org/10.46690/capi.2023.03.0
Multi-label prediction method for lithology, lithofacies and fluid classes based on data augmentation by cascade forest
Get PDFPredicting the lithology, lithofacies and reservoir fluid classes of igneous rocks holds significant value in the domains of CO2 storage and reservoir evaluation. However, no precedent exists for research on the multi-label identification of igneous rocks. This study proposes a multi-label data augmented cascade forest method for the prediction of multilabel lithology, lithofacies and fluid using 9 conventional logging data features of cores collected from the eastern depression of the Liaohe Basin in northeastern China. Data augmentation is performed on an unbalanced multi-label training set using the multi-label synthetic minority over-sampling technique. Sample training is achieved by a multi-label cascade forest consisting of predictive clustering trees. These cascade structures possess adaptive feature selection and layer growth mechanisms. Given the necessity to focus on all possible outcomes and the generalization ability of the method, a simulated well model is built and then compared with 6 typical multi-label learning methods. The outperformance of this method in the evaluation metrics validates its superiority in terms of accuracy and generalization ability. The consistency of the predicted results and geological data of actual wells verifies the reliability of our method. Furthermore, the results show that it can be used as a reliable means of multi-label prediction of igneous lithology, lithofacies and reservoir fluids.Document Type: Original articleCited as: Han, R., Wang, Z., Guo, Y., Wang, X., A, R., Zhong, G. Multi-label prediction method for lithology, lithofacies and fluid classes based on data augmentation by cascade forest. Advances in Geo-Energy Research, 2023, 9(1): 25-37. https://doi.org/10.46690/ager.2023.07.0
Numerical evaluation of hydrogen production by steam reforming of natural gas
Get PDFIndustry-scale hydrogen is mainly produced by steam methane reforming (SMR), which uses natural gas as the feedstock and fuel and co-produces CO2. This study aims to numerically evaluate hydrogen production by SMR under various reacting conditions. Unlike the previous studies with limited scenarios, the performance of SMR is continuously evaluated in a high-dimensional input-parameter space. The SMR plant including a combustor, a reformer, and a water-gas shifter is modeled in Aspen HYSYS software. The four key parameters, including methane fraction of the feedstock, reformer pressure and temperature, and shifter temperature, are treated uncertain and 50 samples are drawn from a four-dimensional parameter space defined by their ranges. Each sample is input to HYSYS model and mass ratio of each component in product streams is obtained as the output variables. Based on the 50 pairs of input-output data, response surfaces of the outputs are developed to surrogate HYSYS models. The fast response surface models are then used to calculate global sensitivity indices and evaluate SMR processes. Results show the reformer performance is controlled by temperature rather than pressure, and a temperature higher than 900 °C can maximize the reaction rate. The water-gas shifting reaction is inhibited in the reformer but significantly enhanced in the shifter. Hydrogen is mainly produced in the reformer while the major function of the shifter is to convert CO to nontoxic CO2.Document Type: Original articleCited as: Chen, M., Al-Subhi, K., Al-Rajhi, A., Al-Maktoumi, A., Izady, A. Al-Hinai, A. Numerical evaluation of hydrogen production by steam reforming of natural gas. Advances in Geo-Energy Research, 2023, 7(3): 141-151. https://doi.org/10.46690/ager.2023.03.0
The effect of fibre swelling on fluid flow in cotton fabrics: An experimental study
Get PDFDesign of hygiene products such as sanitary napkins, diapers, etc. is heavily dependent on the liquid absorption performance of fabrics. As fibres swell upon liquid absorption, their liquid absorption performance changes. Understanding the flow through porous media under swelling conditions has important implications for product design and has yet to be elucidated fully. The goal of our research was to study the effect of fibre swelling experimentally. Cotton is selected as the test fabric as it is commonly used in most hygiene applications. Under swelling conditions, the effect of swelling on individual fibres, porosity, permeability, and performance of the cotton fabric is analysed. Findings showed that upon water absorption, the fibre diameter increased by 10%, porosity decreased by 11%, and permeability decreased by 60% under fully swollen conditions. The porosity reduction is also predicted analytically using the data obtained from the fibre swelling measurements. In contrast, predictions of commonly used analytical models showed only a 30% reduction in the porosity. To correct this, two new correction factors to account for effects of inter-fibre interactions on the total swelling rate of fabric are proposed. The performance measures of cotton samples under swelling conditions indicated that advancement of the flow front on the lower face was more dominant than the upper face of the sample possibly related to gravity. These experimental data improve our understanding of wicking flow which can help to improve the design of hygiene products and to develop more realistic computational fluid dynamics models.Document Type: Original article Cited as: Salokhe, S., Rahmati, M., Masoodi, R., Entwistle, J. The effect of fibre swelling on fluid flow in cotton fabrics: An experimental study. Capillarity, 2023, 6(3): 41-48. https://doi.org/10.46690/capi.2023.03.0
Preparation and investigation of self-healing gel for mitigating circulation loss
Get PDFLost circulation is a common and complex downhole accident in the process of oil and gas drilling. Traditional bridge plugging material has the limitation of poor adaptability to lost formations. Therefore, this study synthesized a new self-healing plugging material to improve the plugging success rate; specifically, the hydrophobic association polymer lauryl methlacrylate-acrylamide-acrylic acid containing Fe3+ was modified via curdlan to form a composite gel with high strength and self-healing properties. The self-healing time, mechanicalness and rheological properties of the self-healing gel were systematically evaluated. The results showed that the modification of curdlan could significantly improve the mechanical properties and rheological strength of self-healing gel, and the chelating structure formed by Fe3+ and carboxyl groups could further enhance the mechanical properties of the self-healing gel. Toughness and storage modulus of the LF0.15C2 selfhealing gel with the introduction of curdlan and Fe3+ could reach 30.2 kJ/m3 and 3,458 Pa, respectively. Compared with conventional gel materials, composite gels with self-healing properties exhibited better pressure-bearing capacity of 2.5 MPa, and could effectively avoid causing plugging at the entrance of the fractures by high-concentration inert material and improve the pressure-bearing capacity. In addition, the plugging mechanism of the self-healing gel modified via curdlan in formation fractures was analysed in detail. The self-healing gel modified via curdlan prepared in this work has application potential as a lost circulation material in the field of oil and gas drilling.Document Type: Original articleCited as: Wang, R., Wang, C., Long, Y., Sun, J., Liu, L., Wang, J. Preparation and investigation of self-healing gel for mitigating circulation loss. Advances in Geo-Energy Research, 2023, 8(2): 112-125. https://doi.org/10.46690/ager.2023.05.0
Improved Duncan-Chang model for reconstituted hydrate-bearing clayey silt from the South China Sea
Get PDFThe experimental testing and analysis of strength and deformation characteristics of hydrate reservoirs is an integral part of natural gas hydrate exploitation. However, studies so far have failed to deeply explore samples from the South China Sea. Especially, there is a lack of a simple and applicable method to estimate their mechanical behaviors. Thus, based on test data, an improved Duncan-Chang model is established in this paper to characterize the strength and deformation of reconstituted samples with various hydrate saturation and stress states from this area. This model can accurately describe the strain-hardening characteristics, and failure strength is estimated by the improved Drucker-Prager criterion with high fitting accuracy. The initial elastic modulus and failure ratio are given by the proposed empirical models, which are obtained from experimental data and fitting methods. Generally, this model has several advantages including simple structure, favorable performances, and a limited number of model parameters. Therefore, it could be widely used in strength and deformation analysis. This study can support the prevention and control of geological risks during natural gas hydrate exploitation in the South China Sea.Document Type: Short communicationCited as: Dong, L., Wu, N., Zhang, Y., Liao, H., Hu, G. Li, Y. Improved Duncan-Chang model for reconstituted hydrate-bearing clayey silt from the South China Sea. Advances in Geo-Energy Research, 2023, 8(2): 136-140. https://doi.org/10.46690/ager.2023.05.0