Fluid Displacement Research Articles

Synthesis and Characterization of Self-Dispersion Monodisperse Silica-Based Functional Nanoparticles for Enhanced Oil Recovery (EOR) in Low-Permeability Reservoirs

A controllable particle size mono-dispersing nanofluid system has been developed to address the challenges of low porosity and low-permeability in low to ultra-low-permeability reservoirs. This system combines high dispersion stability with enhanced oil recovery performance, and its effectiveness in improving recovery rates in low-permeability reservoirs, where conventional chemical flooding is ineffective, has been well demonstrated. Using the in situ method to prepare monodispersed nano-silica particles, the effects of the water concentration, ammonia concentration, and silica precursor concentration on the morphology, particle size, and formation time of the silica spherical particles were analyzed. Building on this foundation, a partially hydrophobic modified nano-silica oil displacement fluid was synthesized in situ. The system’s dispersion stability, ability to reduce oil-water interfacial tension, and capacity to alter rock wettability were evaluated. Core physical models were used to evaluate the oil displacement efficiency and the permeability applicability limits of the self-dispersing nano-silica oil displacement system. The experiments confirmed that the particle size distribution of the self-dispersing nano-silica oil displacement system can be controlled within a range of 10 nm to 300 nm. The nanofluids exhibited excellent stability, effectively altering the rock wettability from oil-wet to water-wet and reducing the oil-water interfacial tension to approximately 10−1 mN/m. The nano-displacement system increased the recovery rate of the low permeability reservoirs by more than 17%. The in situ modification method used to prepare these self-dispersing nanoparticles provides valuable insights for synergistic enhancement of recovery when combined with other systems, such as surfactants and CO2. This approach also opens up new possibilities and drives further development in the field of nano-enhanced oil recovery chemistry.

Improvement and effectiveness analysis of dynamic/static imbibition experiments.

In low-permeability fractured reservoirs, there is a generalized fluid displacement between the replacement fluid in the fracture and the matrix crude oil. This imbibition behavior plays a crucial role in the development of this type of reservoir. The experimental devices for studying static imbibition behavior are generally susceptible to air pollution on the surface of the test core and a long testing period; the experimental devices for studying dynamic imbibition behavior are generally unable to eliminate the driving action. A dual-purpose experimental setup and an experimental method for dynamic or static imbibition that can avoid the above defects were designed. A method of fracture fluid flow rate calculation and motor speed conversion is proposed, and the method is used to assist in setting the parameters of dynamic imbibition experiments. The device was applied to compare the experimental effects with the static imbibition bottle and the dynamic replacement imbibition, respectively, and the effect of fracture width on the dynamic imbibition of repellent oil was investigated. The results show that: the static imbibition recovery rate of the dynamic/static imbibition experimental device is 1.55 percentage points higher than that of the imbibition bottle; the dynamic imbibition recovery rate is 3-6 percentage points lower than that of the driving dynamic imbibition method, and it can reflect the influence of a single flow rate condition on the imbibition; imbibition in low-permeability fractured reservoirs is more likely to take place in the fracture in the interval of 50-100 μm in the width.

Discrepancy in oil displacement mechanisms at equivalent interfacial tensions: Differentiating contributions from surfactant and nanoparticles on interfacial activities

Discrepancies in oil displacement mechanisms at equivalent interfacial tensions were principally explored in the current study, with a novel emphasis on distinguishing the contributions of surfactants and nanoparticles in interfacial activities. The hypothesis was that if both chemicals exhibit similar interfacial activities, the oil displacement outcomes at the capillary scale should be consistent. Otherwise, differences would indicate distinct interfacial behaviors. Fluid displacement experiments were conducted using a two-dimensional micromodel, where nanofluids and surfactant solutions were tested at equivalent interfacial tensions. In the high interfacial tension pair (20 mN/m), the surfactant solution displaced oil more efficiently and rapidly than nanofluids, achieving greater ultimate oil recovery. This difference was attributed to the effective reinforcement of capillary forces in the surfactant system, which drove the displacement process. In contrast, the nanofluids did not achieve the same level of performance due to their limited ability to modify interfacial forces. This finding highlighted the two chemicals’ fundamentally different interfacial activities and oil displacement mechanisms. Furthermore, in the lowest interfacial tensions pair, where the surfactant achieved 6.5 mN/m and the nanofluids 15.6 mN/m, both systems unexpectedly displayed similar oil displacement efficiencies and fingering-like behaviors. This similarity, however, arose from distinct underlying mechanisms: capillary instability drove fingering in the surfactant system, while expansive layer flow induced fingering-like in the nanofluids. These findings challenge the assumption that reducing interfacial tension with nanoparticles is the primary mechanism in enhanced oil recovery (EOR). The study highlighted the need for a more refined understanding of the action of nanoparticle interfacial activities within EOR processes. To further validate these insights, future research should scale up fluid displacement studies to Darcy’s scale using core-flooding tests, enabling a more comprehensive examination of complex two-phase flow dynamics.

Lattice Boltzmann modeling of forced imbibition dynamics in dual-wetted porous media

Forced imbibition dynamics are critical for enhancing recovery rates in reservoirs, as efficient fluid displacement directly impacts resource extraction. This study employs the Zou-He velocity boundary condition and a modified convective boundary condition (mCBC) within the multi-component Shan-Chen lattice Boltzmann method (LBM), thus facilitating unobstructed flow of multi-component fluids at the outlet while maintaining constant outlet pressure. The model's validity was established through outflow tests of immiscible droplets in channels. Its accuracy was further confirmed by comparing results from forced imbibition dynamics tests in dual-wetted pores with theoretical predictions. A symmetrical porous medium was constructed using the stacking method, achieving dual wettability by fixing the contact angle in the upper region and varying it in the lower region. We performed 20 simulation sets under unfavorable viscosity ratios and varying capillary numbers, focusing on overall displacement efficiency before and after breakthrough, and employing energy balance equations to evaluate the dominant forces. Results reveal that capillary forces predominantly dictate forced imbibition dynamics in low capillary number scenarios. In strongly wetted regions, the invading fluid fully occupies pore spaces; however, in weakly wetted regions, displacement efficiency significantly declines as wettability approaches neutrality, even nearing zero. As capillary numbers increase, viscous forces become more prominent, controlling dynamics and leading to fingering and trapping of defending fluids. In weakly wetted areas, the increasing influence of viscous forces enhances fluid displacement, resulting in significant improvements in overall displacement efficiency compared to conditions dominated by capillary forces.

Strong effect of often-overlooked initial spilled oil distribution on subsequent soil remediation: A pore-scale perspective

The removal of spilled oil within soil by water injection is essentially an immiscible fluid displacement process. Numerous studies have been conducted to investigate the way to achieve a higher displacement efficiency. However, these studies often assumed that the pore space was initially saturated by oil only, ignoring the effect of initial oil distribution on the remediation, which led to incorrectly computed flow field and biased analysis. This work aimed to reveal the effect of initial oil distribution on flow physics during the remediation. Based on a pore-scale model and the phase-field method, the spilled oil invasion and remediation in a heterogeneous porous media were investigated, and the dynamic evolution of the phase interface was examined in particular. Four different distribution patterns of spilled oil were obtained through various velocities during the oil invasion stage, which were considered as initial states for the subsequent remediation stage. The results showed that ignoring the oil invasion process led to a more than 10% reduction in the ultimate remediation efficiency. However, the maximum interfacial area of fluids was larger and the obtained relative permeability curve was much smoother for the scenario considering the oil invasion. Besides, a higher initial water saturation led to a lower starting pressure. This work provided new pore-scale insights into the often-overlooked roles of initial phase distribution in fluid dynamics behind the remediation of oil-contaminated soil by water injection, which was of fundamental importance to the development of effective response strategy for soil contamination.

Predictive modeling for coiled tubing fatigue using advanced machine learning techniques

Coiled tubing CT plays Pivotal role in oil and gas well intervention operations due to its advantages such as flexibility, fast mobilization, safe, low cost and wide range of applications, including: well intervention, cleaning, stimulation, fluid displacement, cementing, and drilling. However, CT is subject of fatigue and mechanical damage caused by repeated bending cycles, internal pressure and environmental factors which can lead to a premature failure, high operational cost and production downtime. With the development of CT proprieties and application traditional fatigue life prediction methods based on analytical models integrated in tracking process showed in some cases an underestimate or overestimate of the actual fatigue life of CT particularly when complex factor like welding type, corrosive environment, and high-pressure variation are involved. This study addresses this limitation by introducing a comprehensive machine learning-based approach to improve the accuracy of CT fatigue life prediction, using a data set derived from over 350 tests both lab scale and full-scale fatigue test. The study has incorporated the impact of different parameters such as CT, grades, wall, thickness, CT diameter, internal pressure and welding types. By using advanced machine learning techniques such as artificial network (ANN), Gradient boosting regressor we got a more precise estimation of the number of cycles to failure than traditional models. The results of this study shown the importance of integration of machine learning for CT fatigue life analysis and demonstrating its capacity to enhance the prediction accuracy and reduce the uncertainty. A detailed machine Learning models is presented, emphasizing their capability to handle complex data and improve prediction under diverse operational conditions. This study contributes to more reliable, CT management and safer more cost-efficient well intervention operations.

Temperature prediction of geothermal drilling considering the drilling fluid thermophysical parameters

An increasing number of geothermal wells are being drilled to meet the growing demand for geothermal energy. Given that the harsh environment of geothermal wells exposes drill-following tools to the risk of high-temperature failure, scholars have developed thermo-mathematical models to predict the temperature field distribution in wellbore. To the best of authors' knowledge, most models ignore the interaction between the fluid thermophysical parameters and its temperature. They also overlook the fact that the actual structure of the drilling column causes changes in the convective heat transfer coefficients between the fluid and the well wall, which subsequently affects heat transfer from the wellbore. In this study, we tested the changes of thermal property parameters of drilling fluid with density and temperature. Based on the actual drill string structure and considering the variation in thermophysical parameters during drilling fluids’ circulation, we innovatively established a transient heat transfer model for geothermal horizontal wells with heat–fluid–solid coupling. Subsequently, a drilled geothermal well was used to simulate the temperature during drilling. The effects of the drilling fluid system, density, and displacement, rotary speed, and WOB during drilling on the wellbore temperature distribution were analyzed. Furthermore, suggestions for the selection of drilling fluid and parameters during the drilling process were given. The results of this study can help accurately predict the wellbore temperature of geothermal wells and high-temperature wells, which provides guidance for the rational selection of drilling tools for drilling operations.

Investigation of Backpressure Wave Propagation Properties during Gas Kicks in Managed Pressure Drilling

Summary It is often essential to provide backpressure to the wellbore by changing the opening size of the choke valve when a gas kick is detected during managed pressure drilling (MPD), which maintains the pressure in the bottom of the hole. In this study, a mathematical model was developed to explain how backpressure waves spread and weaken in a wellbore during MPD when there is a gas-liquid two-phase flow. The model is founded on a two-phase flow model, which thoroughly accounts for the gravity, shear force, and interphase interactions between the gas and liquid phases. The small perturbation theory was used to compute the backpressure wave’s propagation speed and attenuation coefficient. The outcome showed satisfactory agreement with other scholars’ experimental results. The model was used to study the impacts of the following variables on the backpressure wave propagation properties: void fraction, temperature, pressure, interphase resistance, shear force, density, invading gas composition, displacement of the drilling fluid, rate of intrusion of gas, gas-liquid surface tension, and drilling fluid viscosity. By using an example well, the laws of pressure wave propagation speed, attenuation coefficient, and propagation time with well depth were analyzed. Through evaluative methods in the field of economic management, the principal control variables governing the propagation of backpressure waves were determined. The conclusion is that, in terms of operational feasibility, lower drilling fluid density and reduced drilling fluid displacement are advantageous for a faster propagation of backpressure waves to the bottom of the well.

Investigation of smoothed particle hydrodynamics (SPH) method for modeling of two-phase flow through porous medium: application for drainage and imbibition processes

The drainage and imbibition processes are critical mechanisms in petroleum engineering. These processes in a porous medium are controlled by surface forces and pressure gradients. The study of these processes in the pore scale by common simulators always has limitations in multiphase flow modeling. Also, obtaining relative permeability curves through laboratory analysis requires expensive equipment. Additionally, these laboratory experiments are quite expensive and may introduce significant uncertainties. For this purpose, this study investigated the creation of relative permeability curves and their effect on oil production. Initially, single-phase fluid and two-phase droplet flow within a fracture with both soft and rough surfaces were utilized to validate the formulation of the Smoothed Particle Hydrodynamics (SPH) method. Then, by using three randomly constructed porous medium models, the imbibition and drainage processes have been studied. Finally, sensitivity study has been carried out on critical parameters related to fluid flow dynamics in the porous environment, including pressure changes, wettability, and heterogeneity in drainage and imbibition processes. The simulation results were consistent with current theories; therefore, it is reasonable to consider SPH to characterize the fluid flow dynamic during the drainage and imbibition processes. According to sensitivity studies, pressure gradient (residual saturation of displaced fluid is about 5.65% and 8.44%) and heterogeneity (the residual saturation of the displaced fluid was 4.04% and 2.98%) have the largest impact on flow modeling in both drainage and imbibition processes and wettability (the residual saturation became 36.62% and 5.12%) has significant effect on the drainage process through porous medium. In general, fluid flow dynamic studies can be performed using the SPH method to model fluid flow in simple and complex porous medium under various flow conditions. The SPH method can also be used as an applicable tool to investigate the hydrocarbon fluids flow within larger geometries in the future.

Study on the Equivalent Density Tool and Depressurisation Mechanism of Suction-Type Depressurisation Cycle

In order to further regulate equivalent circulating density (ECD), a novel downhole apparatus for reducing circulating pressure in high-temperature and high-pressure wells, the suction-type ECD reduction tool, was devised. The utilisation of this tool enables the bottomhole pressure of the equivalent circulating density to be attained in close proximity to its hydrostatic pressure, thereby facilitating the attainment of deeper drilling depths. The tool is composed primarily of a screw motor, scroll blades, annular seals, universal joints, and drilling columns. The tool operates by utilising the suction effect and hydraulic energy extracted from the circulating fluid by the screw motor, which is then converted into mechanical energy to create suction and enhance the flow energy of the drilling fluid within the annulus at the bottom of the well, thereby reducing the equivalent circulating density. Furthermore, based on ANSYS-FLUENT analysis simulations, the alteration of pressure drop characteristics in response to varying drilling fluid densities, displacements, and tool sizes was modelled. The simulation results demonstrate that the pressure drop effect is 1.0 MPa when the drilling fluid density is 1.2 g/cm3, 1.7 MPa when the drilling fluid density is 1.5 g/cm3, and 1.9 MPa when the drilling fluid density is 1.8 g/cm3. A pressure drop of approximately 2.3 MPa was observed when the drilling fluid density was 2.0 g/cm3. The maximum pressure drop is achievable with a flow rate ranging from 1500 to 2500 L/min. A maximum pressure drop of 2.3 MPa is observed when the flow rate is within the range of 1500 to 2500 L/min. Two distinct viscosity values (0.02 and 0.06 kg/(m·s)) were employed to assess the impact of viscosity on pressure drop characteristics in a suction-type ECD tool. The results demonstrated that the pressure drop remained largely unaltered, indicating that viscosity had minimal influence on this parameter. The flow rate emerged as the primary factor affecting pressure drop, with viscosity exerting a relatively minor effect.

Research on the impact of overflow well shut-in on wellbore integrity and safety

If an overflow occurs, the well must be closed immediately. To ensure the safety of the drilling wellbore in ultra-deep wells, it is critical to analyze the transient flow process and pressure fluctuations of the fluid in the annular space of the overflow well shut-in. This paper investigates the pressure fluctuation model of multi-phase fluid in the annular space after overflow occurs during gas well drilling, analyzes the influence factors of multi-phase fluid's pressure wave velocity, and simulates and analyses pressure fluctuation changes in the annular space in light of the impact of overflow well shut-in on wellbore safety. The model's correctness is verified by comparing it to experimental data published in the literature. The model is developed and examined using the example of a genuine gas well in western China. According to the study, as soon as the BOP closes, pressure rapidly increases to a high of 6.09 MPa at 5.89 s before falling to a valley of 4.68 MPa at 35.36 s. When the mild shut-in time lasts 20 s, the wellhead annular pressure reaches a maximum of 5.8 MPa. If the wellhead equipment can withstand the annular space's first pressure wave, a hard shut-in is recommended. To optimize the overflow well shut-in system and ensure wellbore safety, the change in pressure in the wellhead annular space as a result of varied shut-in timings and drilling fluid displacement is studied.

Wetting and pressure gradient performance in a lattice Boltzmann color gradient model

An accurate implementation of wetting and pressure drop is crucial to correctly reproduce fluid displacement processes in porous media. Although several strategies have been proposed in the literature, a systematic comparison of them is needed to determine the most suitable for practical applications. Here, we carried out numerical simulations to investigate the performance of two widely used wettability schemes in the lattice Boltzmann color gradient model, namely, the geometrical wetting scheme by Leclaire et al. [Phys. Rev. E 95(3), 033306 (2017)](scheme-I) and the modified direction of the color gradient scheme by Akai et al. [Adv. Water Resour. 116, 56–66 (2018)] (scheme-II). We showed that scheme-II was more accurate in simulating static contact angles of a fluid droplet on a solid surface. However, scheme-I was more accurate in simulating a dynamic case of a binary fluid flow in a horizontal capillary tube described by the Washburn equation. Moreover, we investigated the performance of two popular pressure gradient implementation types. Type-I used the so-called Zou–He pressure boundary conditions at the inlet and the outlet of the domain, while type-II used an external body force as a pressure gradient. We showed that the type-I implementation was slightly more accurate in simulating a neutrally wetting fluid in a horizontal capillary tube described by the Washburn equation. We also investigated the differences between the two types of pressure gradient implementation in simulating two fluid displacement processes in a Bentheimer sandstone rock sample: the primary drainage and the imbibition displacement processes.

Compound cavity formation and splash crown suppression by water entry through proximally adjacent polystyrene beads

We move forward the important topic of water entry by documenting splash dynamics arising from the impact of hydrophilic spheres with buoyant millimetric microplastics, mimicked in our study by polystyrene beads. Collision with small, buoyant beads is yet another means to manipulate splash dynamics. In this experimental study, we investigate the fluid–structure interactions between beads and hydrophilic spheres for Froude numbers in the range of 20−100. Generally, hydrophilic spheres entering a liquid bath below the critical velocity of 8 m/s produce minimal fluid displacement and no cavity formation. The presence of proximally adjacent beads atop the fluid with respect to impacting spheres promote flow separation and compound cavities for sufficiently large Froude numbers, while suppressing the growth of splash crowns. Compound cavities consist of a shallow, quasi-static first cavity that seals near the water line, and a second, deeper cavity produced in the wake of descending spheres. A vertically protruding Worthington jet follows cavity collapse. The resulting splash metrics differ from those of hydrophobic spheres with respect to the properties of impacted beads. We find impactors traversing a deep liquid pool layered with beads experience drag reduction when compared to entry into a clean pool due to the drag-reducing benefits of flow separation while not offering a high inertial penalty. Our study unravels the physics behind the widely encountered interaction of solid projectiles impacting passively floating particles, and our results translate to the entry dynamics of water-diving creatures and projectiles into water bodies polluted by floating millimetric microplastics.

Chemical-Assisted CO2 Water-Alternating-Gas Injection for Enhanced Sweep Efficiency in CO2-EOR.

CO2-enhanced oil recovery (CO2-EOR) is a crucial method for CO2 utilization and sequestration, representing an important zero-carbon or even negative-carbon emission reduction technology. However, the low viscosity of CO2 and reservoir heterogeneity often result in early gas breakthrough, significantly reducing CO2 utilization and sequestration efficiency. A water-alternating-gas (WAG) injection is a technique for mitigating gas breakthrough and viscous fingering in CO2-EOR. However, it encounters challenges related to insufficient mobility control in highly heterogeneous and fractured reservoirs, resulting in gas channeling and low sweep efficiency. Despite the extensive application and research of a WAG injection in oil and gas reservoirs, the most recent comprehensive review dates back to 2018, which focuses on the mechanisms of EOR using conventional WAG. Herein, we give an updated and comprehensive review to incorporate the latest advancements in CO2-WAG flooding techniques for enhanced sweep efficiency, which includes the theory, applications, fluid displacement mechanisms, and control strategies of a CO2-WAG injection. It addresses common challenges, operational issues, and remedial measures in WAG projects by covering studies from experiments, simulations, and pore-scale modeling. This review aims to provide guidance and serve as a reference for the application and research advancement of CO2-EOR techniques in heterogeneous and fractured reservoirs.

Preparation of a novel MR fluid for squeeze-shear mode by compositing micron-scale and nano-scale particles

The magnetorheological (MR) fluid under the squeeze-shear mode has an enhanced structure by reducing the distance between particles, significantly increasing the yield stress compared to the single shear mode. The existing research on preparing MR fluid is all based on single shear mode. This work mixes micron-scale carbonyl iron powders and micron-scale soft magnetic particles to prepare the specialized MR fluid for the devices working under squeeze-shear mode. Several kinds of micron-scale carbonyl iron powders and micron-scale soft magnetic particles are selected, of which the magnetic properties are tested to obtain the suitable soft magnetic particles for MR fluid. Then, the optimal combination of micron-scale carbonyl iron powders and micron-scale soft magnetic particles is obtained when the orthogonal test is used to compare the yield stress of different combinations. At the same time, the appropriate surfactants and base carrier fluid were selected, according to the previous work. On this basis, the novel MR fluid is prepared by the base fluid displacement method, and its performances are tested. The results show that the sedimentation rate is 0.8 % after standing for 20 days, which can keep the MR device in a stable state. The viscosity of the novel MR fluid is 8.0 Pa·s at room temperature, exhibiting good liquidity, which allows it to be injected into MR devices. The shear yield stress of the novel MR fluid is 60.28 kPa at the squeeze pressure of 600 kPa, which is 1.5 times higher than that under single shear mode, significantly enhancing the mechanical performance of MR fluid. The novel MR fluid with good sedimentation stability, appropriate viscosity, and better mechanical performance can be applied to more MR devices, especially the MR devices under squeeze-shear mode.

An improvement in the method of correcting indirect radial strain measurements during triaxial strength tests in rocks

The present article provides an improvement in the method to correct indirect strain measurements in triaxial compressive strength tests through axial displacement and hydraulic fluid volume change measurements. The improvement focused on reducing the parameters of the formula proposed for indirect volumetric strain in the original method, thereby facilitating the development of a simpler formula in which the radial strain depends on only two parameters: the initial volume of the rock specimen and the volume changes of the hydraulic fluid for each instant. The comparison between the improvement proposed, and original method resulted in a mean absolute difference of 0.003.•This improvement does not depend on the axial strain, unlike the original method, which requires correcting the indirect axial strain measurements before correcting the indirect radial strain measurements.•This improvement can be useful for research on the stress-strain behavior of intact rock under laboratory conditions, such as in the study of the post-peak state.

Cardiovascular effects of long-duration space flight.

Early studies exploring the physiological effects of space travel have indicated the body's capacity for reversible adaptation. However, the impact of long-duration spaceflight, exceeding 6 months, presents more intricate challenges. Extended exposure to microgravity and radiation profoundly affects the CV system. Notable phenomena include fluid shifts toward the head and modified arterial pressure. These changes disrupt blood pressure regulation and elevate cardiac output. Additionally, the loss of venous compression leads to a reduction in central venous pressure. The displacement of fluid from the vascular system to the interstitium, driven by baroreceptor stimulation, results in a 10%-15% decline in plasma volume. Intriguingly, despite potential increases in cardiac workload, cardiac muscle atrophy and perplexing variations in hematocrit levels have been observed. The mechanism underlying atrophy appears to involve a shift in protein synthesis from the endoplasmic reticulum to the mitochondria via mortalin-mediated mechanisms. Instances of arrhythmias have been recurrently documented, although generally nonlethal, in both Russian and American space missions. Long-duration spaceflight has been associated with the prolongation of the QT interval, particularly in extended missions. Exposure of the heart to the proton and heavy ion radiation pervasive in deep space contributes to coronary artery degeneration, augmented aortic stiffness, and carotid intima thickening through collagen-mediated processes. Moreover, it accelerates the onset of atherosclerosis and triggers proinflammatory responses. Upon reentry, astronauts frequently experience orthostatic intolerance and altered sympathetic responses, which bear potential hazards in scenarios requiring rapid mobilization or evacuation. Consequently, careful monitoring of these cardiac risks is imperative for forthcoming missions. While early studies illuminate the adaptability of the body to space travel's challenges, the intricacies of long-duration missions and their effects on the CV system necessitate continued investigation and vigilance to ensure astronaut health and mission success.

Radial displacement patterns of shear-thinning fluids considering the effect of deformation

Radial injection of shear-thinning fluids into rock fractures is ubiquitous in subsurface engineering practices, including drilling, hydraulic fracturing, and rock grouting. Yet, the effect of injection-induced fracture deformation on radial displacement behavior of shear-thinning fluids remains unclear. Through radial injection experiments of shear-thinning fluids displacing an immiscible Newtonian fluid in a Hele–Shaw cell, we investigate the fracture deformation behavior during injection and the fluid–fluid displacement patterns under this impact. A mixed displacement pattern is observed where the invasion front gradually evolves from unstable (viscous fingering) to stable (compact displacement) as the injection proceeds. We demonstrate that the combined effect of shear-thinning property and radial flow geometry plays a controlling role in the evolution of the patterns. At high flow rates, the fracture dilation induced by high injection pressure tends to reduce the displacement efficiency in stages. Based on linear stability analysis, we propose a theoretical criterion for the transition of interfacial stability considering the viscosity of injected fluids and fracture deformation, which agrees well with the experimental observations. This research underscores the importance of rock deformation on two-phase flow dynamics in fractured media.

Computational study of Newtonian laminar annular horizontal displacement flows with rotating inner cylinder

We computationally study the effects of inner cylinder rotation on the laminar displacement flow of two Newtonian fluids along a horizontal eccentric annulus. This flow arises in primary cementing operations in the oil and gas industry, used to seal wells and prevent leakage. We investigate how the rotational motion of the inner cylinder influences the displacement, affecting the interplay of viscosity and density differences, as well as eccentricity. We first simulate a series of experiments recently performed, in order to validate the computational approach. We then study the effects of the rotating inner cylinder in more detail. The rotation shears the fluid in the narrow annular gap and also drags fluid around the annulus, typically resulting in helical streamlines and a spiral pattern of the concentration. Over short timescales, the rotation tends to increase dispersion, but the redistribution of the fluids around the annulus can then improve the overall displacement, i.e., reducing slumping effects due to buoyancy. We also observe a new patterning instability at the inner cylinder, which was not visible in the previous experiments. This instability arises from destabilization of the wall film of displaced fluid, which forms naturally on the walls of the annular gap. We have studied the dimensional parameter space where this instability occurs. Strong buoyancy can suppress the instability, and a threshold value of dimensionless rotation velocity is required for onset of the instability.

The role of nanoparticle–surfactant interactions in air-stabilized foams used for improving oil recovery

Foam flooding, an emerging tertiary oil recovery technique, demonstrates efficacy as a conformance control method in enhanced oil recovery. Conformance control mitigates injected displacement fluid channeling and bypassing, improving macroscopic sweep efficiency. Generated foamed films preferentially enter high permeability zones, diverting subsequent injection into unswept lower permeability regions. Nanoparticle-reinforced foams exhibit consistent bulk stability and effective residual oil mobilization. This work utilizes dynamic foam analysis to probe the synergistic effects of zinc oxide nanoparticles and anionic surfactant on foam generation and persistence. Bulk and local scale foam stability is evaluated under various potassium chloride concentrations. Optimal foam stability occurs near the critical micelle concentration of the surfactant at 2,500 ppm. Increasing electrolyte concentration within a fixed surfactant formulation decreases foam stability due to salt-induced micellar swelling. An optimized electrolyte and nanoparticles with a surfactant combination produce high-quality foam with increased bubble density per unit area. Micellar swelling by nanoparticle adsorption inhibits lamellae thinning and liquid drainage. Enhanced foam properties improve microscopic displacement efficiency and mobility control in foam-assisted oil recovery. Oil recovery is increased by approximately 22% compared to conventional waterflooding.