查看更多>>摘要：The occurrence states (adsorbed or free) directly control the transport and production of shale oil, and free oil is the most common potential product available using existing technologies. A variety of theories and experimental methods have been developed to estimate the adsorbed and free oil amounts in shale pore-fracture systems, however, it is difficult to clarify the microdistribution characteristics of shale oil in in-situ pore systems using these methods. In the study described here, by integrating experimental and theoretical models, an effective method was developed to reveal the microdistribution of oil confined in nanoporous shales from the Dongying Sag, in the Bohai Bay basin, China. Centrifugation-nuclear magnetic resonance (NMR) experiments were com-bined with the modified Langmuir equation, and then applied to estimating amounts of adsorbed and free oil. And the microdistribution characteristics of shale oil were then analyzed by the adsorption ratio theoretical model. Furthermore, the mechanisms of controlling the adsorbed, free amounts and microdistribution of shale oil were also discussed. The primary results demonstrated that the modified Langmuir equation (Langmuir-like equation) was an effective and accurate technique for evaluating the adsorbed and free oil amounts in shales. We estimated that adsorbed and free oil amounts ranged from 5.8023 to 29.7995 mg/g, and from 3.9510 to 25.6410 mg/g, respectively, at a temperature of 20 degrees C, while the adsorbed oil weight ratios were 0.2778-0.7023 (mean 0.5438). The average value of the adsorbed oil density was approximately 2.0231 g/cm(3), which was 2.6994 times that of the free oil. The average adsorbed layer thickness was 0.7433 nm, which equaled nearly two molecular diameters. The adsorbed and free oil microdistribution was clearly described by the adsorption ratio theoretical model and the T-2 spectrum. The adsorbed oil was mainly confined to micropores, while free oil was stored in meso- and macropores-and that pore microstructures affected shale oil microdistribution character-istics. The amount of adsorbed oil was mainly controlled by micropore volume and specific surface area, while the amount of free oil was closely associated with total volume of the larger pores. We also noted that the more complex the pore structure, the lower the free oil content and the higher the adsorption ratio. The amount of adsorbed oil was closely related to the shale composition, and increased with TOC content. The amount (ratio) of adsorbed oil also increased with increasing clay mineral content, and was negatively proportional to the quartz + feldspar content. The authors are confident that the study described in this paper has delivered new insights into the microdistribution of adsorbed and free oil in shale pore-fracture systems.
查看更多>>摘要：An experimental apparatus has been developed to measure the CO (2)solubility in water, brines, polymer solutions, white oil and drilling fluids using the sample analysis method. The experimental results show that the electrolytes can significantly reduce the solubility of CO2 in water and the salting-out effect can be enhanced by increasing the molar concentration of salt ions. The influences of different polymers are similar, which can reduce the gas solubility to a certain extent. Furthermore, CO2 solubility in the oil-based drilling fluid is significantly larger than that in the water-based drilling fluid. Considering the complicated interactions between gas, electrolytes, polymers and base oil in the drilling fluid, a simple and reliable model for predicting the CO2 solubility is developed. Validation of the model calculations against the experimental measurements indicates that the simulation errors of CO2 solubility in the water-based and oil-based drilling fluids are 3.47% and 6.75%, respectively.
查看更多>>摘要：Pour point depressant (PPD) activity mechanisms include solubilization, morphology alteration, and steric/entropic repulsion. A wealth of complex intermolecular interactions governs PPD efficacies in real crude com-positions. The current study utilizes single-component model waxes (n-C24H50, n-C28H58, n-C32H66 or n-C36H74) dissolved in dodecane to reveal chain-length dependent PPD efficacies. Wax appearance temperature depression, effected by PPD, diminishes as paraffin chain-length increases. Stronger London van der Waals attractions be-tween longer wax components effectively diminish PPD solubilization activity. Controlled-temperature centri-fugation reveals partitioning of PPD polymers and paraffin waxes between solid and liquid phases. PPD polymers typically contain a polydisperse molecular weight distribution. The highest molecular weight PPD polymers partition preferentially to solid phases, including PPD aggregates and PPD-modified wax crystals. The lowest molecular weight PPD polymers remain preferentially soluble in the liquid phase, binding only weakly to precipitated wax. The presence of precipitated wax counteracts the solubilization activity of PPD polymer. At high precipitated wax fractions, PPD shows no wax solubilization activity. As the precipitated wax fraction decreases, the wax solubilization activity of the PPD progressively increases. The wax solubilization activity of the PPD attains a maximum at the WAT. Finally, the results are consistent with a single optimal polymer mo-lecular weight for PPD activity occurring at a single temperature. PPD polymers larger than the optimal MW undergo a coil-to-globule transition prior to wax crystallization, deactivating the polymer. Polymers smaller than the optimal molecular weight show weaker binding to wax crystals, consistent with a smaller Gibbs free energy of binding, and partition preferentially to the liquid phase. Modern PPD formulations should utilize polymers that are tailored according to molecular weight. Optimally tailored PPD polymers should be less polydisperse in nature than current PPD formulations.
查看更多>>摘要：The accurate evaluation of microscopic pore structure characteristics of shales is of great significance for shale oil development. In order to gain a better understanding of complicated pore structure of lacustrine shales, silty shale samples from the Upper Triassic Yanchang formation in Ordos Basin were investigated using FE-SEM, N-2 adsorption, MIP, helium pycnometry and Nano-CT. FE-SEM observations show that five typical pores (interparticle pores, intraparticle pores, dissolution-related pores, organic matter pores and microfractures) are developed in shale samples. The full-scale pore size distributions, determined by combining N2 adsorption, MIP and Nano-CT, show that the pore sizes of the samples range from 2 nm to more than 20 mu m, while the dominant pores are in the range of 20-100 nm. A certain difference exits in porosity obtained by Nano-CT, N-2 adsorption, MIP, helium pycnometry and the combination methods. The N-2 adsorption tends to underestimate the total pore volume and porosity. The MIP may overestimate or underestimate the porosity, due to the matrix compression or limited penetration of mercury, respectively. The combined porosity using multiple methods is reasonably consistent with helium pycnometry. Pore network models of these samples are extracted using the centerline algorithm. From the pore network model, the proportion of connected pores of the studied samples ranges from 15.51% to 37.45%. The coordination numbers obtained from pore network range from 1.34 to 1.84, indicating the relatively poor pore connectivity of the studied samples. Samples rich in organic matter have high proportion of connected pores in the region of interest (ROI) of 3D network. Pore throats show preferential orientation in XY plane (parallel to bedding) and then their two diagonal directions, while the Z axis of the pore structure (perpendicular to bedding) is less connected. These parameters improve the understanding on storage space and transport property of lacustrine shale oil.
查看更多>>摘要：This paper deals with the constant bottomhole pressure as one of the common techniques in Managed pressure drilling (MPD), a complex nonlinear process that employs various control strategies to regulate the bottomhole pressure. To have an accurate operation, the nonlinear controllers usually consider the exact model of the system, which leads to a complex structure that sophisticates their practical implementation due to resulting high computational load. In addition to low computational load, control methods must take into account physical/ operational constraints to be implemented in practice. Utilizing the T-S fuzzy modeling approach as well as the idea of the parallel distributed compensation, this paper constructs a simple fuzzy controller based on the system's exact model and proposes the stabilization criteria in the form of linear matrix inequalities. These criteria not only guarantee the system stability but also satisfy the available physical/operational limitations in the drilling process. We then introduce an optimization problem to obtain the controller gains and find the largest space in which the proposed controller ensures both operational restrictions and stability. The simulation results demonstrate that if the initial condition of the drilling process begins within the margins of the pore and fracture gradients, the bottomhole pressure converges to the desired reference value while the pressure window is not violated and the actuator is not saturated. Thanks to the unsaturated controller during the drilling process and also due to the inherent capabilities of fuzzy logic, in the proposed method, convergence occurs earlier than traditional methods while there is less steady-state error.
查看更多>>摘要：To accurately evaluate altered volcanic reservoirs in the Songliao Basin of China and study the effect of alteration on pore structure, this paper established a methodology for log evaluation based on conventional log data. The volcanic reservoir in the Songliao Basin, China is variable in lithology, complex in pore structure and widespread in alteration phenomena. Because of these problems, the conventional charting method is not good at lithological identification, and the reservoir interpretation conclusions based on interpretation of the conventional logging method are not consistent with the actual logging data, making it difficult to carry out accurate logging evaluation. To solve such problems, this study adopted the particle swarm optimization-support vector machine (PSO-SVM) for carrying out lithological identification. Then, alteration factors were established to evaluate the alteration degree of volcanic reservoirs and obtain the altered clay content by fitting to correct the effect of alteration. Designing the volume model that considered altered clay and selecting the Simandoux model that could correct the influence of clay to calculate relevant petrophysical parameters such as porosity and water saturation, thus formed a methodology of logging evaluation suitable for the altered volcanic reservoir in the study area. At the same time, the study found that for different volcanic rocks, the effects of alteration on pore structure are different. An analysis, in combination with alteration factors and T-2 NMR spectra, showed that for the volcanic reservoir of nonsevere alteration, the higher the alteration degree, the greater the total porosity and the void porosity. However, with increasing alteration degree, the effective porosity of andesite was higher, while that of tuff worsened. The findings may provide a new idea for the analysis of the pore structure of altered volcanic reservoirs.
查看更多>>摘要：In recent decades, carbon dioxide (CO2) injection has become a promising technique for enhanced oil recovery (EOR). To design and model the CO2-EOR process in a petroleum reservoir, knowledge of the molecular diffusion of CO2 in oil is required. In this research, the constant volume diffusion (CVD) method is utilized to determine the diffusion coefficient of CO2 in a core saturated with synthetic oil. In addition, the effect of the water saturation level in the core on the resulted diffusion coefficients is examined. This method includes an oil-saturated core, which is in direct contact with a CO2 chamber. CVD tests were conducted at initial pressure and temperature of 410 psi and 64 degrees C for water saturation of 0, 39, and 53%. CO2 is injected from the top of the core and oil is produced from the bottom. Once the CVD initial condition is established, the injector and producer valves are shut-in and the CVD test starts. In the CVD test, the pressure drop data are collected and used to tune the diffusion coefficients using a compositional reservoir simulation model equipped with a developed equation of state. History matching of the pressure decay data is conducted to determine the tuned diffusion coefficients. Experimental results show that the existence of water in the core causes a smaller pressure drop in the system. We find that diffusion coefficients decrease linearly with increasing water saturation in the core operating at the same initial pressure and the system temperature. The presence of water in the core reduces the rate of CO2 diffusion into the synthetic oil. Finally, we present an empirical relationship of the diffusion coefficient and the irreducible water saturation at the proposed lab conditions.
查看更多>>摘要：The Weirong shale gas field, located within a low-steep structural belt in southern Sichuan Basin, China, is characterized by gentle structural deformation. Production results have shown that inter-well interference, also known as fracture channeling, affects the productivity of shale gas wells by facilitating fluid flow between wells along pre-existing natural fractures. In this study, we used core observational data, scanning electron microscopy, and image logging analysis to determine the type, intensity, occurrence, and genetic mechanism of the natural fractures in the Upper Ordovician Wufeng-Silurian Longmaxi Formation. Attributes such as seismic coherence, AFE (fault-enhanced attribute), dip, and curvature were utilized to predict the macro and meso fault fractures in the study area. We modeled the micro fault-fractures using the seismic and tracking algorithm to characterize the faults at multiple scales in the Weirong shale gas field, and then completed a comprehensive evaluation of the overall fracture development patterns with respect to the fracture channeling of neighboring shale gas wells. Results indicate that both horizontal and vertical structural fractures have been developed in the shale reservoir of the Wufeng-Longmaxi Formation in the Weirong shale gas field, although the horizontal fractures heavily outnumber the inclined ones. While a few high-conductivity macro and meso fractures display a NE-SW strike, abundant micro-faults have NE-SW and NWW-SEE strikes. Due to the pre-existing basement faults, stress fields and micro-amplitude structure, the NWW-SEE-trending micro fault-fractures are more active than those oriented in the NE-SW direction. Based on field observations, we conclude that regions with well-developed natural fault-fracture networks are more likely to have experienced fracture channeling between or within the platforms of well groups; and the NWW-SEE-trending micro fault-fractures generate more inter-well interference than the NE-SW-trending ones. Predicting the distribution and understanding the origin of the micro fault fractures make it possible to prevent or mitigate the effects of fracture channeling during the drilling and artificial stimulation of shale gas wells.
查看更多>>摘要：As a potential alternative to Portland cement, geopolymers are getting wider acceptance in the scientific world. On a laboratory scale, the latter is being experimented repeatedly to extract valuable and valid results. To complement the experimental work and to make use of the data that resulted from previous experiments, statistical and mathematical models are developed. This article aims to anticipate test results, extract statistical relationships from measured properties, and therefore minimize the time and trials needed to run experiments in laboratories. Five independent input parameters are measured that cover the SiO2/K2O ratio, temperature, time, liquid to solid ratio and the total water content. For each set of these input variables, the consistency of geopolymers was obtained.Two statistical models have been developed in this regard, the Decision Tree, which is a heuristic machine learning model, and the Logistic Regression which is a probabilistic model that calculates and estimates the probability for a certain mixture, at different time, temperature, and other independent variables, to reach a certain consistency threshold.Both model results indicate sufficient performance, and the modelers can use such methods to predict the consistency (pumping time) trends of an untested geopolymer mixture. The results of our models are further validated by additional statistical tests, such as the receiver operating characteristic curve.
查看更多>>摘要：In this study, to adjust the dew point of natural gas, two methods of Joule-Thomson and mechanical refrigeration have been analyzed in terms of technical, energy and exergy. The basis of design was a natural gas feed with an intensity of 1743 kgmole/h. The initial dew point of the feed before processing was equal to 9.65 degrees C. Comparison of the results showed that the mechanical refrigeration method had much better performance and the energy efficiency in this system was 99.84%, while this value was 97.8% for the Joule-Thomson method. Furthermore, the intensity of gas condensate production, as one of the products of dew point adjustment unit, for mechanical refrigeration that uses propane refrigerant for natural gas refrigeration was estimated as 1842 barrels/day. This value exhibited an increase of 185% compared to Joule-Thomson method. The dew points of produced gas through Joule-Thomson and Mechanical refrigeration processes were -8.4 and -24.91 degrees C, respectively. It implies that the quality of hydrocarbons dew point in the produced gas was much lower for Joule-Thomson unit compared to mechanical refrigeration. However, in terms of exergy analysis, the mechanical refrigeration method had an efficiency of 88.69%, while the exergy destruction rate for this method was 15.78% less than the Joule-Thomson process.
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Elsevier