查看更多>>摘要：Hydrogen as a clean fuel source compared to hydrocarbons has attracted many attentions to mitigate anthropogenic greenhouse gas emissions and meet global energy demand. However, high volatility and compressibility of hydrogen make a challenge for its storage. In this regard, the surface-based hydrogen storage facilities (e.g. aerospace, cryogenic tanks, high-pressure gas cylinders, etc.) have been in operation for decades. Moreover, H2 geo-storage is an effective way to store vast volume of hydrogen in deep underground formations where it can be withdrawn again to generate energy when the need arises. The interaction between the injected hydrogen and resident formation fluids (e.g. water), can strongly influence the H2-flow pattern and storage capacity. In this regard, interfacial tension (y) between hydrogen and brine is a key parameter that influences hydrogen displacement within the geological porous medium. As there is a serious lack of literature on this important subject, we measured H2-brine interfacial tension at various geo-storage conditions for a wide range of pressure, temperature, and brine salinity, using the pendant drop technique. The results of the study indicate that y declined linearly with increasing pressure when temperature and salinity are kept constant. Moreover, a linear reduction in y with increasing temperature was observed under constant salinity and pressure conditions. The results also clearly demonstrate that y increased linearly with brine molality over the whole range investigated. An empirical equation was also developed with which y as a function of pressure, temperature, and brine molality can be predicted. The predictions for data points of this work had a maximum deviation of 2.13% from the experimental data. This work thus provides fundamental data for H2 geo-storage projects, and aids in the implementation of an industrial-scale hydrogen economy.
查看更多>>摘要：The typical carbonate reservoir in the Middle East has huge potential, but due to low permeability and high gas-oil ratio, the characteristics of reservoir saturation and pressure distribution are not clear, which makes reservoir development very difficult. As an intelligent prediction and analysis technique, deep learning provides a novel solution to solve this problem. In this study, firstly, the actual static geological data and dynamic production data from the target reservoir were gathered to provide a data foundation for model training and analysis. And then, Random Forest algorithms, Reservoir Engineering methods, and Kriging interpolation algorithms were selected to predict and supplement the missing data of pressure and saturation field. After that, the Convolutional Long Short-term Memory (ConvLSTM) neural network algorithm was employed to build an optimal model to forecast the oil/water/gas saturation distribution and pressure distribution fields. The results showed that the optimal ConvLSTM model achieved good prediction performance. Not only the calculation efficiency, but also the prediction accuracy was higher, in which the average R~2 was 0.8825 and the average accuracy was 0.865. Furthermore, we proposed five development optimizations for the remaining oil potential tapping strategies according to the prediction results. The workflow proposed in this study provides a new direction for the characterization of saturation and pressure distribution in a typical carbonate reservoir.
查看更多>>摘要：The wear of the all-metal progressive cavity pump (AMPCP) has become one of the main concerns from various field applications of oil production. This work systematically reveals the mechanisms of the wear and lubrication between the stator and the rotor components of the AMPCP when lifting fluids. An efficient simulation strategy is proposed to couple the two simultaneous processes, including the rotor's dynamic behavior and material loss due to wearing. On this basis, a three-dimensional finite element model based on the explicit dynamic method is established to capture the rotation process of the rotor considering the pressure load of the inner fluid. In addition, the frictional contact and wear behavior between stator and rotor is described as well. In this regard, the wear estimation model based on the Archard wear theory is developed to depict the material loss with a geometry update and local remeshing technique, the reliability of which is well verified against experimental results. Based on the statistical results of characteristic contact time (CCT) and characteristic wear band (CWB), the wear pattern is summarized into three distinctive bands denoted by CWB I, CWB II, and CWB III, which occurs at different stages during the operating cycles of AMPCP. In particular, the influence of operational parameters (e.g., rotation speed, clearance, and lubrication) on the wear behavior and its underlying mechanisms are quantitatively revealed and discussed. The results demonstrate that the lubrication effect could substantially reduce the wear degree to extend the service life of AMPCP.
查看更多>>摘要：The rheological properties of waxy crude oil are important for its economical and safe pipeline transportation. In actual pipeline transportation, waxy crude oil often exhibits nonlinear rheological characteristics, among which viscoelastic-thixotropic characteristics are the main ones, while there are currently few related studies. This article carried out a study of large amplitude oscillatory shearing (LAOS) for typical Daqing waxy crude oil, and conducted analysis of the nonlinear rheological characteristics of the low temperature waxy crude oil based on the periodic strain loading mode. Using the Fourier transform rheology, Lissajous curve, and stress decomposition method, the effects of strain amplitude and frequency on the nonlinear rheological characteristics under LAOS conditions are analyzed. Results show that when the Fourier transform method analyzes the non-linear rheological characteristics area, the relative intensities of frequency triple and frequency quintuple increase with the increase of strain amplitude and frequency, and it cannot accurately reflect the non-linear rheological properties of waxy crude oil under high-frequency conditions. The Lissajous curve method is more suitable for the study of the nonlinear rheological characteristics of wax}' crude oil under low frequency conditions and establishing a prediction formula of dissipated energy density. In addition, the nonlinear viscoelastic parameters obtained by the stress decomposition method can accurately characterize the nonlinear viscoelasticity of waxy crude oil. This research deeply explores the nonlinear rheological properties of waxy crude oil, which can provide theoretical guidance for practice.
查看更多>>摘要：To investigate the influence of microbial wax removal and viscosity reduction technologies on the fluidity of waxy crude oil, this study took the waxy crude oil from Chinas Daqing Oilfield as the experimental object for microbial wax removal and viscosity reduction experiment. First, utilizing standard strain screening and culture protocols, a high-efficiency microbial strain H-1 (Ochrobactrum intermedium) was proposed from in situ soil. The single factor experiment and multi-factor response surface analysis were then utilized to optimize the temperature, initial pH value of the medium, and NaCl mass concentration needed for the strain's growth. Oil displaced activity and emulsification tests were used to evaluate the bio surfactants produced by the metabolism of strain H-1, and Fourier transform infrared spectroscopy was used to identify the types of biosurfactants. Finally, the application effect of strain H-l on wax removal and viscosity reduction of waxy crude oil were clarified through the wax crystal morphology, wax content, and viscosity of waxy crude oil. The research findings indicated that strain H-l produced best at a temperature of 38.5 °C, pH value was 7.1 and the mass fraction of NaCl was 0.64%. The lipopeptide biosurfactant produced by strain H-l can displace oil. Additionally, strain H-l has a high emulsifying capacity, with a 61.25% emulsifying coefficient. After 7 days of treatment with the strain H-l, the wax crystal morphology of the waxy crude oil changed from a large-sized aggregated to a small-sized sparse condition, and the wax content of the waxy crude oil fell by 38.67%. The viscosity reduction rate of strain H-l to waxy crude oil was consistently greater than 30% over the temperature range of 30-42 °C, with the greatest rate of 42.38% at 39 °C. The preceding results demonstrate that strain H-1 can degrade the wax components of waxy crude oil, lower the crude oil's low temperature viscosity, and then improve the crude oil's low-temperature fluidity.
查看更多>>摘要：In petroleum drilling and completion, the transports of solid particles through drill pipe, dill-hole annulus and fractures are important dynamic processes. Unlike particle transport in infinite space, the transports of cuttings, proppant and formation sand are hindered by finite boundary. Therefore, accurately describing particle transport behavior in different vessels is conducive to improving drilling safety and efficiency, especially with the rapid development of coiled tubing drilling and hydraulic fracturing technology. In this study, the particle settling experiment was carried out to study the particle settling behavior in the pipe, annulus and parallel plates filled with power-law fluids, involving the particle Reynolds number of 0.01-123.87, the dimensionless diameter of 0.20-0.80, the flow index of 0.48-0.69. Firstly, the wall effect of annulus is revealed through analyzing the settling process of the particles. Then the geometric continuity among the pipe, annulus and parallel plates was determined by introducing the ratio of inner diameter to outer diameter of the annulus, further the unified dimensionless diameter was defined to confirm the relationship between the three in terms of wall effect. In addition, a dimensionless term independent of settling velocity is introduced to establish a unified explicit settling velocity equation applicable to tubes, annulus and fractures with mean relative error of 9.36%. Finally, a calculation example is provided to clarify how to use the explicit model of settling velocity. This paper is the first study of annulus wall effects based on geometric continuity and will provide theoretical guidance for improving cuttings transport, proppant placement and sand management.
查看更多>>摘要：Neural networks are a potential method to solve partial differential equations (PDEs) without considering equation discretization, linearization, and solving large sparse linear systems. Some data-driven or physics-informed methods are studied for surrogate modeling and uncertainty quantification tasks for PDE systems. Compared with data-driven methods, physics-informed methods reduce the reliance on labeled data and have better generalizations and broader applications. However, the methods have low accuracy for solving non-stationary problems with strong nonlinearities. This paper proposes a physics-informed method to solve a porous flow equation with a single source or sink as the boundary condition. The present network framework consists of two network modules. The first module uses two hidden layers with frozen weights, obtained by pre-training a simple double hidden layer network using boundary conditions and initial conditions as loss functions. The second module is used as a residual module to learn measurable label data to improve the accuracy of the solution on the nonlinear boundary. The numerical results verity the validity of the PDE solution, and the results show that the method performs better in terms of both solution and prediction than existing methods. In addition, the method allows a good inversion of the permeability from the measurable data.
查看更多>>摘要：Due to the combined advantages of injecting CO2 for boosting natural gas recovery efficiency and sequestration of CO2 in depleted shale gas reservoirs, the enhanced gas recovery (EGR) approach has recently attracted the attention of researchers. To analyze the viability of the increased gas recovery technique, many published studies were reviewed based on theoretical, experimental settings, and simulation models in this manuscript. The underlying link between geological and petrophysical factors is discussed, as well as how they affect CO2 and CH4 sorption. According to numerous studies, 30-55 percent of the CO2 injected into the shales is adsorbed on the pores surface of the rock matrix, resulting in CH4 desorption and additional natural gas recovery of 8-16 percent. For the application in diverse shales reservoir conditions, the best fit adsorption models (Langmuir, Ono Kondo, and D-A) were summarized. The theoretical findings of this work are anticipated to add to current studies on CO2 adsorption and sequestration, as well as CH4 desorption characteristics and the myriad simulation studies have revealed that well spacing, fracture permeability, injection pressure and strategies are key consideration for effective field demonstration for CO2-EGR projects. Despite the availability of theoretical explanations, experimental verification, and modeling findings, field-scale trials remain limited due to the risk of CO2-CH4 mixing and the high cost of capturing, purifying, and re-injecting CO2 into depleted reservoirs. Furthermore, the unpredictable heterogeneity of the shale formation still poses challenges on the gas recovery. The setbacks and limitations highlighted in this study will encourage academia and researchers to conduct more research into appropriate EGR technologies and their economic implications.
查看更多>>摘要：The Qianjiang inter-salt shale oil reservoir has a high content of salt minerals such as glauberite and halite. Salt dissolution and recrystallization will occur during the water injection development process, which will lead to changes in the porosity and permeability of the reservoir. At present, there is a lack of models and numerical simulation methods to characterize this phenomenon. Using theoretical derivation combined with laboratory experiments, programming and numerical simulation, a characterization model and reservoir numerical simulation method that can describe changes in reservoir porosity and permeability caused by salt dissolution and re crystallization have been established. Studies have shown that salt dissolution will increase the porosity and permeability of the reservoir, and the magnitude of the change is proportional to the amount of water passing, which can improve the flow ability of shale oil. To the contrary, recrystallization will cause the porosity and permeability of the reservoir to decrease, and therefore in the development process, salt crystallization inhibitors should be added to the injected water to avoid salt crystallization blocking the reservoirs around the well and wellbore and causing production decline or even shut-in.
查看更多>>摘要：The method of nanofluid flooding to enhance heavy oil recovery has attracted much attention in oilfields. An EOR technology named alkali-silica nanoparticle-polymer (ANP) flooding was designed to enhance heavy oil recovery. The performance of the ANP flood system on reducing interfacial tension (IFT), altering the wettability of rock surface, emulsifying and displacing heavy oil were compared with that of polymer (P), alkali-polymer (AP) and nanoparticle-polymer (NP) flood systems. Visual flooding test was conducted to investigate the displacement mechanisms of different flood systems in porous media. ANP nanofluid could remain stable over 30 days without sedimentation of nanoparticles. The emulsifying ability of the four flood systems for heavy oil followed the order: P < NP < AP < ANP. Based on the analysis of droplet size distribution of emulsion and changes of IFT value with alkali concentration, the best formula of ANP system to emulsify heavy oil was 0.3% [w/v] Na2CO3 + 0.1% [w/v] silica nanoparticle + 1000 mg L~(-1) polymer. Electrostatic repulsion between silica nanoparticles and oil droplets played a dominated role on stabling ANP emulsion. ANP flood system could change the wettability of rock surface to a more water-wet state (contact angle varied from 85.4° to 35.6°). Core and visual flooding tests proved that ANP flood system had a better sweep and displacement efficiency for heavy oil than other three flood systems (P, AP and NP), which could enhance heavy oil recovery by 21.19% after water flooding in a sandstone core. Emulsification is the main mechanism for ANP flooding to enhance heavy oil recovery.
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