Oil Flow Research Articles

Consideration of surface roughness during the design of internal structures for fluid transport produced by additive manufacturing of PEEK

Additive manufacturing offers new possibilities for the design of structural components used in fluid transport. Sections of hydraulic manifolds or hydraulic blocks, parts of fluid pumps or hydraulic motors can now be manufactured with details which were not achievable with conventional manufacturing technologies, e.g., optimization of internal bends to minimize pressure drops or decrease peaks in velocity fields of fluids. However, as geometric features influence operational conditions of structural elements, pressure drop and velocity field also depend on the wall roughness of internal bends. This feature thus also has to be taken into account when designing the internal structure for the given fluid and operating conditions. In this paper, a study on surface roughness produced with additive manufacturing of polyether ether ketone (PEEK) is presented. PEEK is known for its excellent thermal and mechanical properties, resistance to wear, chemicals, and temperature which makes it an exciting material choice for structural elements with exceptional performance characteristics. First, flow of water and oil through a round pipe produced with additive manufacturing has been simulated. Two models have been used in simulations, a simplified pipe with a prescribed wall roughness and a detailed pipe with modeled surface roughness. Pressure losses and velocity fields in the pipe were then calculated. Finally, an experiment has been set to measure the pressure losses which are compared to the simulated values.

An experimental study on air-oil flow patterns in horizontal pipes using two synthetic oils

Investigations on the gas-oil mixture flow of highly viscous oils have become increasingly significant in various industries for the past couple of years. This study examines the characteristics of air-oil flow patterns to understand the effect of the oil phase's thermophysical properties and flow rates on flow patterns. An experimental study was conducted to visualize the air-oil mixture flow in horizontal pipes. The diameters of the horizontal pipes were selected as 20 and 40 mm, respectively. Two different oils having substantially different viscosities were employed as the liquid phase. Based on the visualization results, air-oil mixture flow is categorized into seven flow patterns: stratified smooth, stratified wavy, annular, plug, slug, bubbly, and dispersed bubble flows. Along with representative images, this study demonstrates the essential characteristics of individual flow patterns. Furthermore, it discusses the influence of each phase's flow rate, oil viscosity, and surface tension on flow patterns. The processes of liquid entrainment in stratified wavy flow, bubble tip breakup in plug flow, and liquid slug aeration in slug flow are also illustrated, respectively, with the corresponding sequential representative images and schematic diagrams.

Food vs packaging: Dynamics of oil migration from particle systems into fibrous material

Paper packaging for compacted or tabletted foods is seen as a key sustainable packaging of the future. Yet its fibrous structure is susceptible to absorb oils, fats, greases and other small molecules from the contacting food. Underlying phenomena associated with oil release from compacted food on fibre-based packaging, such as viscous liquid flow, capillarity, and gravity from compacted particle systems into fibre networks are not fully understood yet. As such, oil stain mitigation on packaging remains a challenge. Using model food tablets of 95% 500 and 50 μm particle size with 5% sunflower oil as the liquid phase, this work employed for the first-time quantitative Raman spectroscopic chemical imaging (RCI) coupled with automated image quantification for comparison of oil flow dynamics between food compacts and contacting paper packaging. The extent of de-oiling from the compact and imbibed into paper showed similar exponential decay with time for both porous systems. For the first time, oil migration dynamics on the food compact surface was 2D visualised via Raman spectroscopy and showed markedly different trends with varying environment climatic conditions and compact microstructure. The larger particle system leaked up to 50% of oil into paper, whereas the 50 μm system retained 100% of its oil, creating an effective internal oil barrier. This novel technique opens the way for further understanding liquid transfer between porous food media and harnessing microstructure engineering to increase food and packaging performance.

Experimental Study on Flow Characteristics of Oil-Water Two-Phase Flow in Single-Node Cross Fracture

Single-node cross fracture is the basic unit of discrete fracture network. In this paper, the flow characteristics of oil-water two-phase flow in single-node cross fracture model are investigated by experimental method. The model was divided into sixteen groups according to different angles, the oil and water phase flow rates were changed sequentially in each group and the velocity of oil and water phase were controlled to be in the low velocity flow rate range all the time during the experiment. The fluid flow process was recorded during the experiment by using the high-speed camera and the results were analyzed in detail. Under the condition of low velocity flow, oil-water two phases were slug flow in fracture. Effects of fracture crossing angle and oil-water phase velocity on the length of water section and the ratio of water-oil section length were also considered. The peristaltic pump speed is used instead of flow rate for the discussion, and the results show that for the same cross-fracture angle model, when the water pump speed is unchanged, the length of the water section gradually decreases in the form. of a power function with the increase of the speed of the oil pump. When the oil pump speed is unchanged, as the water pump speed increases, the length of water section increases in the form. of a linear function and the length ratio of wateroil section increases in the form. of the power function. Under different speeds of oil pump and water pump, the influence of fracture crossing angle on the length of water section and the length ratio of water-oil section is different.

Transient Flow Characteristics of a Pressure Differential Valve with Different Valve Spool Damping Orifice Structures

Lubrication system failure is a significant cause of in-flight shutdown incidents in aviation engines. The pressure differential valve, an essential component of a certain type of aviation engine lubrication system, is responsible for controlling the flow rate and pressure of the lubricating oil. Comprehending the transient flow characteristics of the pressure differential valve is of paramount importance for the secure operation of lubrication systems. This paper establishes a transient flow model of a pressure differential valve based on a transient computational fluid dynamics (CFD) method, and the experimental validation demonstrates the effectiveness of the computational model. The internal flow characteristics of the differential pressure valve at different stages during the opening process were studied. Additionally, four transient lubricating oil flow models with different valve spool damping orifice were established to analyse the impact of damping orifice structure on valve spool movement characteristics, pressure control characteristics, and flow field distribution. The results indicate that when the diameter of the valve spool damping orifice increases from 0.3 mm to 1.0 mm, the valve spool displacement and fluid force increase by 88 % and 20 %, respectively. Meanwhile, the peak valve spool velocity, peak oil supply pressure, and steady-state value decreased by 15 %, 29 %, and 34 %, respectively. As the length of the valve spool damping orifice increases from 0.894 mm to 4.0 mm, the growth rate of valve spool displacement and fluid force gradually decreases, with the peak valve spool velocity decreasing by 7 %. This study has potential significance for the structural optimization and application of pressure differential valve in lubrication systems.

Removal mechanism of adhering heavy oil from pipeline wall in low-temperature flow

With the global emphasis on heavy oil development and increasing water content in Chinese oilfields, the low-temperature flow of heavy oil has been widely concerned. Integrating experiments and theoretical modeling, a hydrodynamic balance model for removing adhering heavy oil from pipeline wall was proposed to determine the temperature threshold for heavy oil transportation (adhesion temperature, AT). Two forms of heavy oil removal from pipeline wall were identified in the study: slide and lift-off. At low temperatures, the abrupt increase in wall-adhesion mass is primarily due to the inability of oil droplets to be removed through lift-off, but rather only through slide. Therefore, the temperature marking the transition from lift-off to slide is suggested as the AT criterion. Predicted AT values were in effective concordance with experimental values, with a maximum deviation of 3.78 °C. ATs for oilfields were predicted, and field cooling transportation tests showed no significant pressure drop increase, indicating the model's practical applicability. Additionally, the influence factors of the model were analyzed based on considerations of adhesion force and hydrodynamic removal force. This study aims to reduce heating energy consumption and carbon emissions during transportation under the premise of ensuring safe flow of high water-content heavy oil.

Prediction of Production-Inflow Profile of a Well Producing Single-Phase Flow of Slightly Compressible Fluid from Multilayer Systems by Temperature and/or Pressure Transient Data

Summary This study focuses on the prediction of the production-inflow profile of a well producing a single-phase flow of slightly compressible fluid (water or oil flow) in a multilayered system using the layer permeability and skin values estimated by history matching spatial and temporal temperature and/or pressure data sets along the completion interval. Such data may be acquired by wireline formation testing, production-logging-tool (PLT), or distributed temperature sensing (DTS) fiber-optic cables. We use an in-house thermal, transient coupled reservoir/wellbore simulator developed during this study. It solves transient mass, momentum, and energy conservation equations simultaneously for both reservoir and wellbore. The effects of the Joule-Thomson (J-T), adiabatic expansion, conduction, and convection are all included for predicting the flow profiles across the wellbore. The results from our in-house simulator are verified with the results from a commercial simulator for the single-phase fluid flow of a vertical well producing geothermal brine and oil in a two-zone multilayer system. We also compare the results from our rigorous transient coupled wellbore/reservoir model with the results from a model assuming steady-state thermal wellbore model used in the previous studies. We find that the steady-state thermal wellbore model used in the previous studies that ignore accumulation terms in mass, momentum, and thermal energy balances is a reasonably accurate model for predicting wellbore pressures and temperatures when it is coupled with a nonisothermal reservoir model for slightly compressible fluid because the transient effect in the wellbore is less important with the slightly compressible fluid. We investigate the nonlinear parameter estimation problem based on the use of single or multiple observed temperature and/or pressure (if available) profiles recorded spatially inside the wellbore and at the sandface. The purpose is to identify if the wellbore or sandface data profiles are more useful to accurately estimate the permeability and skin information and predict a production-inflow profile of the well depending on the representation of an actual multilayer system by a reduced-layered or fine-layered model. We show that using an upscaled-layered model (e.g., representing each heterogeneous layer with a lumped single layer with uniform permeability and skin) provides estimates that are more toward the thickness-average permeability and skin factors of the layers and may not provide a good prediction of the well’s production-inflow profile. We show that including the sandface temperature data in regression worsens, while the use of wellbore temperature data sets improves the quality of parameter estimation if an upscaled multilayered model is used. We also show that regressing on multiple temperature profiles, preferably at the sandface, alone could be used to predict the production-inflow profile accurately if a “fine” multilayered heterogeneous model is used. We also investigate if including or excluding the temperature and/or pressure measurements at the nonperforated sections along the completion interval could help enhance the parameter estimation problem. The results show that when multiple profiles of temperatures including the data at nonperforated zones at different production rates are regressed, reliable estimates of the individual layer properties that predict the production-inflow profile accurately can be obtained, though layer permeability and skin factors may often exhibit wide 95% confidence intervals and high correlations among them. Adding sandface or wellbore pressure data, if available, into observed data sets in history matching always improves the quality of parameter estimation.

Hydrodynamic resistance of pore–throat structures and its effect on shale oil apparent permeability

Oil transport is greatly affected by heterogeneous pore–throat structures present in shale. It is therefore very important to accurately characterize pore–throat structures. Additionally, it remains unclear how pore–throat structures affect oil transport capacity. In this paper, using finite element (FE) simulation and mathematical modeling, we calculated the hydrodynamic resistance for four pore–throat structure. In addition, the influence of pore throat structure on shale oil permeability is analyzed. According to the results, the hydrodynamic resistance of different pore throat structures can vary by 300%. The contribution of additional resistance caused by streamline bending is also in excess of 40%, even without slip length. Furthermore, Pore–throat structures can affect apparent permeability by more than 60% on the REV scale, and this influence increases with heterogeneity of pore size distribution, organic matter content, and organic matter number. Clearly, modeling shale oil flow requires consideration of porous–throat structure and additional resistance, otherwise oil recovery and flow capacity may be overestimated.

Validation of a RANS Turbulence Model for a S833 Wind Turbine Airfoil With a Trailing Edge Flap Using Oil Visualization and Pressure Taps

Abstract The aerodynamics of a small wind turbine blade was captured using a γ–Reθ k–ω shear stress transport transitional turbulence model tuned with production limiter coefficients at a Reynolds number of 1.70×105. The computational fluid dynamics simulations were validated against wind tunnel experiments that included airfoil pressure tap measurements and surface oil flow visualization (SOFV) to capture the flow field. The uniqueness of this blade included a trailing edge flap that was 20% of the chord controlled using a servomotor. The test matrix included angles of attack (AOA) between 1 deg and 7 deg with flap angles of 10 deg in the upward and downward position. Two locations were always observed on the airfoil: a leading edge region of high shear and a midsection of flow separation. Within the flow separation section, two distinct regions existed: a complete detachment of flow from the airfoil surface creating a stagnation region which was followed by a reverse flow region. A third location of flow reattachment near the trailing edge was observed for all cases excluding a downward angled trailing edge flap. The utilization of the flap resulted in changes to the size of the separation zone and the movement of the separation zone along the chord. The numerical skin friction coefficient, oil residue profiles from the SOFV, and pressure tap measurements all showed onset of separation locations on the chord within 10%. The computational fluid dynamics model also predicted the coefficient of pressure across the chord of the airfoil within 10% in comparison to the experimental measurements.

Study on the efficiency characteristics of a stacked cone two-dimensional piston pump

This paper proposes a two-dimensional piston pump with a stacked cone-roll structure. The pump rotates continuously while also moving back and forth in the axial direction. It utilizes the suction and discharge ports to alternate the flow of oil, ensuring proper distribution and completing the suction and discharge process. The operating mechanism of the piston pump was analyzed, and subsequently, a mathematical model was developed to determine its mechanical efficiency and volumetric efficiency was established. Furthermore, the AMESim simulation model was built to obtain the variation curves of the input torque and leakage flow of the drive unit under different load pressures and rotational speeds. Ultimately, a prototype was fabricated and a test apparatus was assembled to evaluate the volumetric efficiency and mechanical efficiency under varying speeds and load pressures. The empirical findings were largely congruent with the modeling findings, indicating that the volumetric efficiency rose from 86.3% to 92.2% as the speed increased, whereas the mechanical efficiency declined from 93.8% to 89.1% under a constant load pressure. Under constant speed conditions, the volumetric efficiency of the stacked tapered roller-type two-dimensional piston pump fell from 94.1% to 91.3% as the load pressure increased. However, the mechanical efficiency grew from 87% to 90.2%. These findings confirm the practicality of the pump design.

Transforming Industry Through Hydraulic Solutions, Enhancing Productivity

This study investigates the workings of such systems in Indonesia, focusing on the flow and pressurization of oil from reservoirs through pumps to working cylinders. Hydraulic systems are crucial in transforming oil fluid pressure into mechanical work, particularly in injection molding machines. Findings indicate that the pump's ability to convert and transmit mechanical energy effectively is pivotal in enhancing machine efficiency. These insights highlight potential areas for improvement in system design and operation, suggesting that optimizing filtration and pressurization could significantly boost industrial productivity and sustainability. Highlights: Hydraulic systems in Indonesia studied for oil flow and pressurization. Pump efficiency crucial for enhancing machine productivity. Optimization of filtration and pressurization can boost industrial sustainability. Keywords: Hydraulic System, Injection Molding Machine, System Works

Enhancing energy efficiency and heat transfer performance of engine oil flow through hybrid nanoparticles in convergent/divergent channel

Engine oil (EO) is employed as a lubricant in various machinery engines. Efficient heat transfers are a fundamental requirement for all processes. To improve heat transfer rates and reduce the energy loss caused by high temperatures, this study focuses on incorporating Iron Oxide (Fe3O4) and Cupper Oxide (CuO) into the engine oil as suspended particles. However, the focus of this research paper is to analyze entropy generation in a convergent/divergent channel that contains a hybrid nanofluid. Mathematical modeling is utilized to present the continuity, momentum, and energy equations. Using the resemblance transformation variables, the governing dimensional partial differential equations (PDEs) are transformed into a system of non-dimensional ordinary differential equations (ODEs), which are then resolved in ascending order through the BVP4c scheme. The graphical results illustrate the effects of various parameters on fluid velocity, temperature, entropy generation, and Bejan number. The study explores changes in velocity profiles under different Hartmann numbers, revealing opposing variations in divergent and convergent channels. Velocity profiles exhibit similar patterns when varying the porosity parameter. In the convergent passage, a higher porosity parameter results in a higher temperature field. Entropy rises against Eckert and Hartmann numbers in both Convergent and Divergent cases. These insights aid in designing and optimizing machinery engines.

Influence of non-intersecting cemented natural fractures on hydraulic fracture propagation behavior

Fractures in deeply buried or formerly deeply buried rocks commonly contain mineral deposits having varying degrees of strength. Understanding how cement deposits in fractures interact with hydraulic fractures (HFs) is important for hydraulic fracture design for practical engineering applications such as enhanced geothermal fluid circulation or oil and gas production. Using discrete element methods, we describe a fully fluid-solid coupling numerical model simulating hydraulic fracture propagation to investigate the influence of cemented natural fractures (CNFs) that do not intersect the predicted path of hydraulic fractures on HF propagation morphology. The fracture morphology depicted by the numerical model aligns well with analytical solutions, indicating the reliability of the simulation results. Using this model, we delved into the effects of fracture cement strength and position, fracturing fluid viscosity, and induced stress field on the interactive propagation patterns of fractures. The simulation results indicate that the HF is captured by weakly non-intersecting CNF, causing the activation of the CNF and the development of cracks primarily caused by tensile failure. As the HF approaches the CNF, the induced tensile stress region at the fracture tip offsets toward the CNF, resulting in fracture reorientation. When the cementing strength ratio between pre-existing natural fracture and reservoir matrix is less than 0.5, it is beneficial to activate CNF and enhance reservoir permeability. The seepage of low-viscosity fracturing fluid into the reservoir significantly enhances the ability of the HF and non-intersecting CNF to communicate with each other, thereby providing favorable pathways for oil and gas flow. The research findings offer valuable insights into fracture network connectivity and permeability enhancement, contributing to enhanced reservoir stimulation strategies.

Modelling and simulation of a novel liquid air energy storage system with a liquid piston, NH[formula omitted] and CO[formula omitted] cycles for enhanced heat and cold utilisation

A liquid piston system (LP) is proposed to recover energy during the discharge of a liquid air energy storage (LAES) plant. The traditionally used air turbine is replaced with an LP system which will expand the evaporated air to generate power. Moreover, an NH3 and transcritical CO2 cycle are integrated to enhance heat and cold utilisation. The integrated LAES system was modelled using gPROMS. The numerical results have a maximum discrepancy of less than 6.4% from experimental data previously reported in the literature. The round-trip efficiency (RTE) was studied for various scenarios, including the sensitivity to thermal oil flow rate and heat exchanger efficiencies. Additionally, the study examined the influence of several LP configurations and concluded with a comparison to a conventional LAES system. With a liquefaction pressure of 40 bar, the highest RTE reached was 37%, surpassing the conventional LAES system’s 25% RTE at a discharge pressure of 25 bar. The heat utilisation was 96%, which doubles that of the conventional LAES system, while the cold utilisation was enhanced by 10%. Furthermore, the LP, NH3, and CO2 cycles thermal efficiencies were 88%, 19%, and 30%, respectively. A detailed energy assessment for heat and cold utilisation is presented.

A novel approach of composite turning for compacted graphite iron using minimum quantity lubrication and liquid nitrogen jetting by a developed setup

Compacted graphite iron (CGI) has high mechanical strength, and low thermal conductivity and content of sulfur, becoming a difficult-to-machine material. The tool life for machining grey cast iron (GCI) is 10–20 times of that of CGI, which greatly affecting the mass production in engine industry. To overcome this challenge, the influence of different spray positions on cooling and lubrication efficiency is analyzed based on the boundary layer theory, and a novel approach of composite turning with MQL lubricating flank face and liquid nitrogen (LN2) jetting cooling rake face is proposed. In virtue of boundary layer theory, negative graded pressure forms during the movement between the workpiece and cutter, resulting in that the MQL oil flows quickly to the contact area on flank face, which improves the lubrication effect. LN2 jetting is employed to cool rake face, effectively avoiding the accumulation of cutting heat on the tool and workpiece. The effects of four different cooling methods, including cutting fluid, MQL, LN2, and MQL + LN2, on the surface roughness, tool wear, and cutting force of cutting CGI and grey cast iron (GCI) were studied. According to the failure criterion of a cutting tool for the wear length of 200 μm on a flank face, the cutter life of cutting length is 2886 and 3884 m, correspondingly by cutting fluid and MQL + LN2, and the cutter life is increased by 34.6 %. In addition, the cutting force during turning CGI is 75.1 and 61.8 N by cutting fluid and MQL + LN2, respectively, and the cutting force is decreased by 17.7 %. The developed setup and findings provide a new turning method to cut a difficult-to-machine material for the use in mass production of the engine industry.

Mechanism of action of Geobacillus stearothermophilus on different shapes of residual oil

Feeding on crude oil and activator in porous medium, microbes remain active on the Oil-water interface under simulated reservoir conditions. At the same time, microbes degrade the residual oil and change the wettability of pore wall. Consequently, the displacement exhibits a decrease of 51.86% in membrane residual oil and an increase of 17.44% in recovery compared with water flooding. The Geobacillus stearothermophilus producing bio-emulsifier and its metabolic products can effectively emulsify reservoir crude oil and reduce the oil-water interfacial tension. In the end and the formed emulsion featured high viscosity can improve the oil flow rate and expanded wave volume of injected fluid. Correspondingly, the cluster-like, columnar residual oil were reduced by 64%, 68% respectively. In the micro porous test cell, the in-situ cultured microbes rely on specific life activities (interfacial tropism and in situ metabolism, etc.) to strip the residual oil off the wall of orifice deep inside the blind-ends, which cannot be achieved by the exogenous injection method. After the in-situ microbial culture process, the residual oil in deep blind-ends was reduced by about 47%, and the recovered oil was increased about 15% compared with exogenous injection method.

The economics of waste oil recycling in the EU

ABSTRACT In 2018, 1.6 million tonnes of waste oil were collected in the European Union. About 61% of the waste oil was regenerated – i.e. it was turned into base oil again – and 39% followed energy recovery pathways either in the form of conversion to fuel or via direct incineration. Although the life-cycle literature largely agrees that regeneration outperforms energy recovery in the EU in terms of greenhouse gas emissions and societal costs, policies to boost regeneration and their socio-economic impacts remain underexplored. We fill this gap by discussing policies for managing waste oil flows and by systematically assessing their socio-economic impacts. We analyse different policies that would induce an increase in the regeneration rate of waste oil from the current 61% to either 70% or 85% and assess how the type and magnitude of impacts as well as their distribution across different actors varies, depending on the policy design. The policies lead to a net saving in terms of avoided societal costs and to moderate gains in employment. However, when accounting for estimated administrative costs, these benefits are likely insufficient to justify regulatory intervention.

Experimental investigation of secondary flow losses in a variable geometry linear turbine cascade with winglet tip

Variable geometry turbines (VGT) hold a crucial role in gas turbines and variable cycle engines (VCE) by allowing adjustments to different operational conditions. In order to realize the adjustable function of the VGT stator blade, there will be partial gap structure at both ends of the stator blade, which will lead to partial leakage flow and serious secondary flow loss at the blade end that cannot be ignored, especially in a large angle adjustment range. At present, there are few researches on turbine cascades considering the real partial gap structure and winglet tip, and the numerical simulation calculation is mainly used, while the in-depth study using wind tunnel test is rarely seen. Therefore, this study attempts to analyze the internal flow characteristics of variable geometry turbine cascade by using five-hole pneumatic probe scanning and surface oil flow visualization, and discusses the mechanism of controlling partial clearance leakage flow and reducing secondary flow loss in the cascade by using winglet tip flow control technology. The winglet offset distance and the change of the relationship between the pivot and the clearance position on the flow field and flow loss is studied experimentally for the first time. The results show that the influence mechanism of winglet tip applied in VGT partial gap is quite different from that of typical blade tip clearance application, and more consideration should be given to the influence of pivot structure. Reasonable parameter selection can achieve a maximum loss reduction of 13.4 % and 20.2 % with and without pivot, respectively, while the unreasonable flow control scheme may lead to the loss or even increase with pivot. The interaction between the new secondary flow structure induced by pivot in the gap and other gap leakage flows is analyzed to explore the new mechanism of using winglet tip to reduce the loss of gap leakage flow.

A semi-analytical rate-transient analysis model for fractured horizontal well in tight reservoirs under multiphase flow conditions

Abstract Rate-transient analysis (RTA) has been widely applied to extract reservoir/fracture properties using analytical and semi-analytical methods with simplifying assumptions. However, current RTA models may lead to misdiagnosis of flow regimes and incorrect estimates of reservoir/fracture information when complex fracture network, multiphase flow, and pressure-dependent properties occur in tight reservoirs simultaneously. A semi-analytical model is developed to account for multiphase flow, complex fracture network, and pressure-dependent properties. The technique uses the black oil formulation and butterfly model to determine three nonlinear partial differential equations (PDEs) that describe the flow of oil, gas, and water in the reservoir with complex fracture network. A modified Boltzmann variable considering the heterogeneity of complex fracture network is proposed to convert the fluid flow PDEs to a set of ordinary differential equations (ODEs) that can be solved through the Runge-Kutta method. A new rate-transient analysis workflow is also developed to improve flow regime identification (ID) and the accuracy for tight oil reservoirs with complex fracture network. It is applied to a synthetic case with equivalently modeled complex fracture network and multiphase flow. The estimated fracture properties are in excellent agreement with model inputs.

Simultaneous adjustment on the CO2/oil and CO2/water interface tensions using hydrophilic, lipophilic and CO2-philic surfactants during CO2 flooding to enhance shale oil recovery after hydraulic fracturing

It is an urgent demand to further enhance shale oil recovery after large-scale hydraulic fracturing with a low oil recovery. CO2 flooding technology has been demonstrated to effectively develop shale oil, however, the residual water after hydraulic fracturing can influence the efficiency of CO2 flooding because of the high CO2-water interfacial tension. Here, the hydrophilic, lipophilic and CO2-philic surfactants were investigated to simultaneously adjust the CO2/oil and CO2/water interface tension to accelerate the oil and water flows to enhance shale oil recovery. The results show that the low-carbon alcohol polyoxyethylene polyoxypropylene ether has the hydrophilic, lipophilic and CO2-philic properties. The alkyl chain length and PO groups have great influence on the interfacial tension of CO2-oil, while the presence of EO groups can significantly reduce the interfacial tension of CO2-water. The surfactant of C4EO3PO6 can not only demonstrate the best performance in reducing the interfacial tensions of shale oil-CO2 and water-CO2, but also decrease the minimum miscibility pressure (MMP) of the shale oil-CO2 system to 18.89 MPa from 24.10 MPa. The interfacial tension between water and the CO2 + 1.0 wt% C4EO3PO6 system can be decreased to 6.62 mN/m at 28 MPa and the reduction rate is 56.10 %. The enhancement of surfactants on the extraction effect of CO2 and the mutual diffusion process between CO2 and shale oil or water interface is the major mechanism to decrease the interfacial tensions. Therefore, the addition of surfactant in CO2 can simultaneously decrease the interfacial tensions of CO2-oil and CO2-water and has a potential to enhance shale oil recovery by reducing the capillary resistance of residual water after hydraulic fracturing and increasing the miscibility between CO2 and oil.