查看更多>>摘要：Dimethyl ether (DME) is arousing attention as a novel water-soluble additive in oil industry. The accurate prediction of phase behavior of DME and water system is crucial important for DME-based research. An equation of state has been a powerful tool for solving phase equilibrium problem, which is based on an ideal molecular force model with binary interaction coefficients reflecting the deviation of a non-ideal system. However, the current knowledge of interaction coefficient is limited by obtaining from backward by using phase equilibrium data. This leads to the unclear meaning of the interaction coefficients, insufficient response to the molecular force interaction relationship at the molecular level and no ability to predict phase equilibrium properties without primary use of experimental data. To overcome this, in this study a correction by combining an activity coefficient and a linear solvation energy relationship (LSER) has been proposed to address the solubility deviation from an idealized model. This deviation at the micro level indicates the deviation of nonideal molecular forces from the ideal Raoult's law. Based on this novel correction, binary interaction coefficients have been obtained with a more practical molecular interaction relationship, which leads to more consistent results with experimental data from the literature. Moreover, in asymmetric phase systems, concentration-dependent binary interaction coefficients have been proposed based on previous discussion to represent intermolecular forces in non-ideal phase systems. Furthermore, partitioning coefficients, which lead to a potential criterion for solvent selection for heavy oil recovery, have been discussed from the perspective of intermolecular forces. This study provides new insights into non-ideal phase behavior. By combining a LSER and activity coefficients, a quantitative analysis on non-ideal molecular behavior and related complex phase problems becomes possible.
查看更多>>摘要：Spontaneous imbibition has been proved to be a promising enhanced oil recovery method for tight reservoirs, but the mechanisms of spontaneous imbibition oil recovery (SIOR) are still unclear. Here, we use the self-prepared novel lower-phase nano-emulsion (LWPNE) to reveal the mechanisms. In LWPNE solution, nano-scale oil drops (NODPs) in 6 nm diameter are formed and dispersed with co-presence of micelle solubilizing N-hexane. The effects of LWPNE on both interfacial tension (IFT) and contact angle were studied at 0-10,000 mg/L salinity condition, and spontaneous imbibition efficiency was determined from imbibition experiments in Amott cells at 60 degrees C. Electron Microscope and Transmission Electron Microscope were used to analyze the emulsification and solubilization mechanisms of LWPNE. Experimental results show that the original 135 degrees (oil-wet) contact angle can be reduced to 32.7 degrees (water-wet); the IFT is decreased to 0.0038 mN/m, and electrolyte has no contribution to either IFT reduction or wettability alteration. The average oil recovery from spontaneous imbibition testing using 0.3 wt% LWPNE is 44.1%, which is 20.5% higher than that from systems at similar conditions but using brine only. The LWPNE can solubilize oil by increasing NODPs' sizes to average 36 nm in diameter, which is the dominant mechanism to improve SIOR for LWPNE. The solubility of LWPNE is evaluated by the diameter growth rate of NODPs, and once it reaches 350%, a self-driving force drives oil drops to move forward. Moreover, the transformation mechanisms of spontaneous imbibition modes from imbibition to drainage are revealed by using the imbibition discriminant parameter (Nxe213; 1
查看更多>>摘要：There is a wealth of experimental evidence that fracture initiation and breakdown pressures differ depending on in-situ stress status, rock properties, and injection conditions. However, the mechanism is not fully understood from a theoretical modeling perspective. In this study, a fully coupled plain-strain fracture model is proposed to interpret the mechanism of fracture initiation and breakdown pressures. The fracture model consists of fracture initiation and propagation governed by linear elastic fracture mechanics. The effects of wellbore compliance (or compressibility), solid-fluid coupling, and fracture multiscale propagation behavior are fully considered. The solid-fluid coupling equations are solved using the Newton-Raphson iterative method. The explicit time marching method is used to capture the fracture initiation process. An implicit time-stepping with the fracture tip asymptotic solution is used to capture fracture propagation fronts. The model is validated against the analytical solutions of the plane-strain model. Sensitivity analysis demonstrates that the initiation pressure mainly depends on rock properties, especially the fracture toughness. The peak pressure (breakdown pressure) is related to rock properties and injection conditions and usually occurs before the peak of the pressurization rate is reached. It increases with the injection rate, fluid viscosity, Young's modulus, and fracture toughness. The dimensionless inlet flux into the fracture can be used to determine the fracture initiation pressure. The pressurization rate during the fracture initiation stage is constant and can be used to assess wellbore compliance. Using a low injection rate and a low-viscosity fluid is beneficial to capturing the fracture initiation pressure. This study can help understand fracture initiation and propagation and interpret hydraulic fracture initiation and breakdown pressures.
查看更多>>摘要：Deep fractured vuggy reservoirs are characterized by complex structures, harsh formation conditions and strong heterogeneity. Accordingly, foam stability was first assessed under high-temperature, high-pressure conditions. A microetched physical model mimicking the fractured vuggy reservoir was constructed. Then, the static features of the foam in the model was inspected. The flow characteristics and EOR mechanism of foam flooding in the microetched model were analyzed. Foam stability results show that at low pressures, the foam volume first increases and then decreases with increasing temperature. With increasing pressure, the influence of temperature on foam stability gradually declines. Within the microetched model, the foam displayed better fluidity in karst caverns, whereas better static stability is attained in the fractures. Gravity impacted oil recovery during water and foam flooding. Bottom water flooding induced uniform rise of the oil-water interface, hence achieving highest oil recovery of 49%. Foam flooding following helped recovering residual oil near the top of the caverns. Employing high-velocity foam flooding following low-velocity foam flooding increased the sweep efficiency of oil entrapped in the dead-end pores. Coupling bottom water flooding with foam flooding is the most promising technique.
查看更多>>摘要：The flow dynamics of foam in porous media during enhanced oil recovery (EOR) and aquifer remediation is an area of active research. Foam performance therein is dependent on the strength and stability of the foam. Limiting capillary pressure, apparent viscosity, texture, mobility reduction factor, resistant factor, and trapped gas saturation are often used as indicators of foam strength and stability. However, there are contradictory reports on the direction of the correlation between foam strength and the absolute permeability of porous media. Some literature reported that foam strength increases with decrease in permeability and vice versa, while some others reported an opposite trend. Since foam transport in porous media is a vast field of research, this paper focuses only on the review of the parameters often used in the literature to characterize strength and stability of foam, and the correlations between these parameters and the absolute permeability of reservoir rocks. We highlighted sources of contradictions, mainly the interchangeable use of the mentioned performance indices to describe foam strength and stability, and sometimes the failure to differentiate between strength and stability of foam. Appropriate clarifications are made based on published data and we highlighted areas that require further research.
查看更多>>摘要：An appropriate shut-in after fracturing can dramatically enhance performance of wells in shale gas reservoirs. In this study, a novel wettability index and mineral content curve based shut-in time optimization approach was proposed. First, a new experimental device for spontaneous imbibition of fracturing fluid under the conditions of formation temperature and confining pressure was designed. Then, we conduct a set of experiments on shale samples from the Longmaxi Formation (LF) in the Sichuan Basin to measure the water-wet index and determine the critical value of clay content. Finally, the low-field nuclear magnetic resonance (NMR) equipment was used to monitor the water flow in shale micro-pores, based on this, the shut-in time for different shale reservoirs was optimized. The experimental results show that LF shale hydration can induce new micro-fractures, and the fractures shape is mainly shale bedding fractures, with obvious directionality. The clay content is the key factor affecting water wettability of shale and the critical clay content value of type I and type II shale reservoirs was about 39.5%. The optimal shut-in time of type I and type II shale reservoirs are about 20 days and 15 days respectively. Field application of three wells showed that the average daily gas production was increased by 2-3 times. The research results can guide the development of shale gas reservoirs effectively.
查看更多>>摘要：Thermal Enhanced Oil Recovery (TEOR) for heavy oil reservoirs involves the simultaneous flow of oil and steam, mimicking the gaseous phase with an elevation in the temperature. While implementing the TEOR process, reservoir performance prediction tools require the water/oil and gas/oil relative permeability data. Many studies reported the temperature effect on two-phase water/oil relative permeability despite knowing that steam or vapor is conventionally injected, mimicking the gaseous phase during heavy oil recovery. Thus, this requires the knowledge of temperature effect on two-phase gas/liquid relative permeability as well. However, limited studies are reported in the literature regarding the temperature dependency of relative permeability in gas/liquid systems; offer no census about its effects. The scarcity of such studies in the literature is due to the lack of systematic experimental studies and complications observed while conducting the higher temperature tests to mimic the thermal EOR. Hence, the objective of this study was to examine the temperature effect on two-phase gas/liquid relative permeability at varying temperatures from 64 to 132 degrees C using a systematic and reliable experimental process. In this study, Poly Alpha Olefin (PAO-100) was used as the oleic phase, deionized water as the immobile phase, and nitrogen gas as the displacing phase in a clean unconsolidated sandpack under the confining pressure around 1000 psi. Furthermore, Johnson-Neumann-Bossler (JBN) method was opted to interpret the two-phase gas/liquid relative permeability curves from the displacement data, i.e., cumulative oil production and pressure drop measured across the sandpack. The experimental observation suggests that irreducible water saturation and endpoint oil relative permeability are temperature independent. The residual oil saturation decreased with the increase in temperature and led to a higher endpoint relative permeability to gas. On the other hand, the oil relative permeability at equal saturation uplifted, suggesting the enhanced mobility of oil through pores with increasing temperature. On the other side, the gas relative permeability at equal saturation was temperature insensitive other than at residual oil saturation. Also, the two-phase flow region increased with the rise in temperature as both the relative permeability curves shifted upwards, and the broader curve was observed. Hence, this study strongly suggests that the reservoir engineers or commercial reservoir simulators should account for the temperature effects on two-phase gas/oil relative permeability to efficiently predict heavy oil reservoir performance and management during the thermal enhanced oil recovery process (TEOR).
查看更多>>摘要：Fracture is the primary channel of gas seepage in coal seams and controls the drainage efficiency of coal bed methane (CBM). However, the seepage characteristics and dynamic evolution law in the fractures of gas-bearing coal under external loads are yet to be clearly revealed. In this study, an industrial computer tomography (CT) scanner equipped with a triaxial loading system was used to conduct gas-seepage and CT scanning experiments under triaxial compression conditions. The results showed that the fracture volume and permeability decreased first and then increased during the complete stress-strain process of gas-bearing coal, displaying an approximate U-shaped variation trend involving a decrease stage, an increase stage, and a jump-increase stage. The lattice Boltzmann method (LBM) was applied to make the seepage processes of gas-bearing coal reappear, and a modified nonlinear permeability model was developed to represent non-Darcy seepage inside fractured coal. The LBM simulation results mirrored the dynamic evolution of the gas seepage field and gas permeability controlled by fracture propagation. The proposed modified nonlinear permeability model effectively reflected the nonlinear variation behaviour of gas permeability and was superior to the traditional Darcy's model in describing nonlinear seepage of gas-bearing coal.
查看更多>>摘要：Removal of ions from produced crude oil necessitates desalting with water. During desalting it is essential to remove aqueous impurities from oil to avoid corrosion and fouling in upstream oil industry as well as catalyst deactivation in downstream processing. It is also important to simultaneously minimize the environmental impact of produced wastewater by cost-effective industrially feasible techniques. Since the ion content of wastewater discharge of oil desalter unit is far from saturation, its reuse for further desalting of crude oil is proposed in this study. Biocompatible carboxymethyl cellulose (Walocel), two methyl cellulose with different methyl and 2-hydroxypropyl derivative contents (Methocel K3 and Methocel E5), and cellulose acetate, are used to promote demulsification of well water-and lagoon wastewater-in-crude oil emulsion. Screening bottle tests revealed that Walocel and Methocel E5 are more suitable. Walocel and Methocel E5 at 3000 ppm could remove 97.6% and 91.7% of well water from oil at 80 degrees C. It was observed that presence of hydrocarbon impurities and previously added demulsifier in lagoon wastewater greatly enhances initial demulsification rate for Walocel and Methocel E5 up to 5.5 and 19.6 times, respectively. Walocel and Methocel E5 at a final concentration of 3000 ppm could remove 93.5 +/- 3.6% and 95.8 +/- 4.2% of lagoon wastewater within 60 min at 80 degrees C and finally remove all oil content of the emulsion. Superior performance of Methocel E5 in complete demulsification of lagoon wastewater-in-oil is attributed to abundance of hydrogen bond forming oxygen atoms in its cellulosic backbone as well as amphiphilic 2-hydroxypropyl and hydrophobic methyl side chains which constructively interact with water molecules and hydrocarbon impurities in the lagoon wastewater. The results of this study revealed that reuse of oily wastewater in crude oil desalting may be practical and such demulsification could be fast.
查看更多>>摘要：Capital and operating expenses of polymer injection projects are sometimes borderline to ensure profitability. Therefore, it is of interest to significantly improve the oil recovery potential with a low enough marginal cost. The addition of surfactant is very effective to enhance oil recovery, but, with traditional formulation guidelines, the high cost of chemicals and the difficulties in preparing the SP solution is major obstacles. The objective of this study is to try to adapt the concept of optimal surfactant formulation, without trying to achieve ultra-low interfacial tensions, to improve the overall efficiency of polymer injection. Phase behaviors of conventional surfactants/crude oil/water systems have been studied to find the optimal formulation conditions at high surfactants concentration. This ultra-low tension formulation was then diluted by more than one order of magnitude compared to "traditional" surfactant designs and was successfully tested in core floods at different injected volumes in order to optimize the design and minimize the cost. Contrary to expectations, it was found that the optimal formulation used at ultra-low concentrations can sufficiently modify the flow propagation to significantly improve polymer flood. The volume of surfactant injected was optimized to be "good enough" just to upgrade polymer flood without seeking complete desaturation. The low formulation concentration level makes it easy to handle and can considerably extend the application limits of polymer injection.
NSTL
Elsevier