Displacement Efficiency Research Articles

Study on increasing polymer gel strength with Janus nanoparticles and its feasibility in profile control and water plugging

In formations subjected to prolonged flooding, dominant channels are formed in high permeability layers, thereby reducing the displacement efficiency in medium- and low-permeability layers. In this study, the Janus synthesis method was employed to produce Janus Nano-TiO2 with a particle size range of 60–120 nm and superior dispersion properties. These nanoparticles were subsequently combined with polyacrylamide to formulate a high-strength polymer nano-gel for water plugging applications. The successful synthesis of the material was confirmed through FTIR and TGA. Gelation experiments indicated that the gelation strength and time augmented significantly with the increased addition of Janus-T6. Conversely, an increase in temperature or salinity resulted in a reduction of both gelation strength and time. Rheological experiments demonstrated a decrease in polymer viscosity with rising shear rates or temperatures, revealing significant shear thinning behavior in the water-plugging agent solution. System viscosity increased with more Janus-T6. Flow experiments revealed decreasing resistance coefficients at higher permeabilities, while all cores exhibited plugging rates above 85%. Additionally, the breakthrough pressure continuously rose with the increased addition of Janus-T6. Ultimately, displacement experiments indicated a 22.83% increase in the recovery rate after employing PNG plugging followed by secondary water flooding, compared to primary water flooding alone.

Implementing PSO-LSTM-GRU Hybrid Neural Networks for Enhanced Control and Energy Efficiency of Excavator Cylinder Displacement

In recent years, increasing attention has been given to reducing energy consumption in hydraulic excavators, resulting in extensive research in this field. One promising solution has been the integration of hydrostatic transmission (HST) and hydraulic pump/motor (HPM) configurations in parallel systems. However, these systems face challenges such as noise, throttling losses, and leakage, which can negatively impact both tracking accuracy and energy efficiency. To address these issues, this paper introduces an intelligent real-time prediction framework for system positioning, incorporating particle swarm optimization (PSO), long short-term memory (LSTM), a gated recurrent unit (GRU), and proportional–integral–derivative (PID) control. The process begins by analyzing real-time system data using Pearson correlation to identify hyperparameters with medium to strong correlations to the positioning parameters. These selected hyperparameters are then used as inputs for forecasting models. Independent LSTM and GRU models are subsequently developed to predict the system’s position, with PSO optimizing four key hyperparameters of these models. In the final stage, the PSO-optimized LSTM-GRU models are employed to perform real-time intelligent predictions of motion trajectories within the system. Simulation and experimental results show that the model achieves a prediction deviation of less than 3 mm, ensuring precise real-time predictions and providing reliable data for system operators. Compared to traditional PID and LSTM-GRU-PID controllers, the proposed controller demonstrated superior tracking accuracy while also reducing energy consumption, achieving energy savings of up to 10.89% and 2.82% in experimental tests, respectively.

A study on the microscopic mechanism of oil displacement in an adaptive profile control and plugging composite displacement system

This study employed a self-designed microfluidic chip with visualized oil displacement technology and indoor core flooding experiments to reveal the microscopic plugging and adjustment mechanisms. Additionally, it involved the microscopic oil displacement mechanism of an adaptive plugging and flooding composite system containing PPG (preformed particle gel) particles and two blended surfactants. The results indicated that microfluidic imaging captured the dynamic seepage characteristics of PPG particles after swelling, which involved plugging, deformation, and passage through a 0.3 mm throat in a series of pores, achieving adaptive plugging between the size of PPG particles and the pore size. The plugging mechanism of PPG particles involves blocking larger parallel pores, increasing the displacement velocity in smaller pores, and dynamically adjusting the plugging to achieve simultaneous displacement in the high- and low-permeability layers. The displacement mechanism of PPG particles in the simulated pores includes reducing seepage radius, expanding sweep area, and repeatedly overcoming capillary forces. The pressure variation data along the length of different permeability long cores demonstrated that the pressure drop within the first third of the injection end increases with an increase in permeability. The pressure change curve illustrates the migration characteristics of PPG particles in the pore throats, characterized by “accumulation and plugging–pressure increase–deformation and migration.” After injecting the adaptive plugging and flooding composite system following polymer flooding, the flow fraction in the high-permeability layers decreased to 25.65 %, whereas that in the low-permeability layers increased to 74.56 %. The difference in the water flooding pressure before and after implementing the adaptive plugging and flooding system reached a factor of 29, and the oil recovery rate improved by 5.55 % compared to a weak alkaline ternary composite system. The adaptive plugging and flooding composite system demonstrated a synergistic effect in expanding swept volume, blocking preferential flow channels, and enhancing oil displacement efficiency. It achieved the effects of simultaneous plugging and flooding, dynamic plugging adjustment, and synchronized displacement in the high- and low-permeability layers, thereby significantly improving the mobilization of residual oil after polymer flooding.

Experimental Study on Improving the Recovery Rate of Low-Pressure Tight Oil Reservoirs Using Molecular Deposition Film Technology

The intricate geological characteristics of tight oil reservoirs, characterized by extremely low porosity and permeability as well as pronounced heterogeneity, have led to a decline in reservoir pressure, substantial gas expulsion, an accelerated decrease in oil production rates, and the inadequacy of traditional water injection methods for enhancing oil recovery. As a result, operators encounter heightened operational costs and prolonged timelines necessary to achieve optimal production levels. This situation underscores the increasing demand for advanced techniques specifically designed for tight oil reservoirs. An internal evaluation is presented, focusing on the application of molecular deposition film techniques for enhanced oil recovery from tight oil reservoirs, with the aim of elucidating the underlying mechanisms of this approach. The research addresses fluid flow resistance by employing aqueous solutions as transmission media and leverages electrostatic interactions to generate nanometer-thin films that enhance the surface properties of the reservoir while modifying the interaction dynamics between oil and rock. This facilitates the more efficient displacement of injected fluids to replace oil during pore flushing processes, thereby achieving enhanced oil recovery objectives. The experimental results indicate that an improvement in oil displacement efficiency is attained by increasing the concentration of the molecular deposition film agent, with 400 mg/L identified as the optimal concentration from an economic perspective. It is advisable to commence with a concentration of 500 mg/L before transitioning to 400 mg/L, considering the adsorption effects near the well zone and dilution phenomena within the reservoir. Molecular deposition films can effectively reduce injection pressure, enhance injection capacity, and lower initiation pressure. These improvements significantly optimize flow conditions within the reservoir and increase core permeability, resulting in a 7.82% enhancement in oil recovery. This molecular deposition film oil recovery technology presents a promising innovative approach for enhanced oil recovery, serving as a viable alternative to conventional water flooding methods.

Activated single nucleotide mismatch determination through toehold-embedded hairpin-mediated strand displacement reaction alongside CRISPR-Cas12a for detection of TP53 point mutation

The CRISPR-Cas12a-based diagnostic platform is renowned for its high sensitivity and, when coupled with the toehold-mediated strand displacement (TMSD) reaction, enables the detection of single nucleotide mismatch (SNM). However, conventional TMSD with the CRISPR-Cas12a system suffers from signal leakage due to overlapping activator sequences and low displacement efficiency. Here, we propose a toehold-embedded hairpin-mediated strand displacement (THMSD) method and leverage the magnesium attenuation effect of CRISPR-Cas12a for selective single-point mutation detection in the TP53 gene. This approach effectively mitigates signal leakage as the hairpin DNA retains partial crRNA targeting sequences within its loop, preventing sequence overlap with the trigger and direct Cas12a activation. Additionally, the magnesium attenuation effect reduces background signal and enhances selectivity. We investigated toehold length and mismatch position to detect SNM with a high discrimination factor (DF). This high DF allows the THMSD/CRISPR-Cas12a system to differentiate between TP53 R273H mutant and TP53 wildtype genes for cancer screening at low abundances, down to 0.1 % with a concentration of 20 pM. When used for screening between H1975 and WI38 cells, the statistically significant difference was attainable with polymerase chain reaction (PCR) template loading as low as 4 ng. These results pave the way for developing CRISPR-Cas12a-based methods to effectively detect TP53 mutations as lung cancer biomarkers.

Microscopic Experiments to Assess the Macroscopic Sweep Characteristics of Carbon Dioxide Flooding

The Lunnan oilfield in the Tarim Basin, one of China’s major onshore oilfields with substantial geological reserves, faces particular challenges due to the complexity of its reservoir environment and the dispersion of remaining oil. Carbon dioxide, a greenhouse gas, presents an opportunity for enhanced oil recovery (EOR) and geological storage. In this context, the use of carbon dioxide for EOR can simultaneously address environmental concerns and improve oil recovery rates. This study focuses on the TI reservoir in the No. 2 well area of the Lunnan oilfield, employing advanced techniques to analyze the micro- and macro-characteristics of carbon dioxide flooding. Results: From the microscopic point of view, carbon dioxide flooding is mainly miscible with crude oil, which has a strong component exchange effect and can be displaced in the form of full pores, and the microscopic displacement efficiency is close to 100%. Macroscopically, under the combined injection and production of different injected hydrocarbon pore volume multiples (HCPVs), it is injected at the upper and lower layers of the interlayer and produced far away from the lower layer of the interlayer, with a total recovery rate of 52.83%. With the increase in the HCPV, the recovery increased rapidly at first and then slowly, and the HCPV at the demarcation point was 0.5, while the oil production rate increased in a wave-like manner and then decreased rapidly, and the HCPV at the breakthrough point of TI gas was 0.5. However, when the upper and lower layers far away from the interlayer are injected at the same time, the upper and lower layers of the interlayer are produced at the same time, and the total recovery rate can reach 83.02%. With the increase in the HCPV, the recovery rate increases rapidly at first and then slowly, and the HCPV at the turning point is 6.52. The oil production rate increases in a wave-like manner, then decreases rapidly, rises rapidly, and then decreases slowly in a wave-like manner. The HCPV at the breakthrough point of TI gas is 0.63, and the HCPV at the injection–production transition point is 0.63. The total recovery rate of carbon dioxide miscible displacement can reach 88.68% under the condition of separate injection and combined production with different injected hydrocarbon pore volume multiples. With the increase in the HCPV, the recovery increased rapidly at first and then slowly. The HCPV at the demarcation point was 6.5, the oil production rate increased in a wave-like manner, then decreased rapidly, increased rapidly, and then decreased slowly in a wave-like manner. The HCPV at the breakthrough point of TI gas was 0.63, and the HCPV at the injection–production transition point was 6.5. The research results provide data support for the physical reality of the microscopic and macroscopic sweep characteristics of carbon dioxide flooding in the Lunnan oilfield, Tarim Basin.

Fluorescence visualization dynamics of carbonated water injection processes in homogeneous glass micromodels

Understanding the flow behavior of oil–water phases in porous media is crucial for revealing the kinetic mechanisms underlying oil–water movement. In this study, we designed and constructed a fluorescence visualization experimental platform for carbonated water injection (CWI). We evaluated the effects of nine distinct injection rates on oil production and CO2 sequestration capabilities using three types of homogeneous porous structure micromodels. The microscale oil–water seepage behavior at the pore scale was also explored. The experimental results indicate that optimally increasing the injection rate can improve displacement efficiency, whereas excessively high rates may lead to viscous and capillary fingering. The geometry of the micromodels, particularly the hexagonal matrix, demonstrates potential advantages in enhancing oil displacement due to its uniform flow paths. The capillary number (Ca) significantly influences oil droplet capture behavior within micromodels. For instance, micromodel A captures the largest ganglion area at low Ca values, with a noticeable reduction in average ganglion area as Ca increases. Conversely, micromodels B and C exhibit similar trends in ganglion size variation at high Ca values, suggesting a more uniform impact of pore structure on oil droplet capture behavior. At elevated Ca values, capillary forces exert a more uniform and controlled effect on oil droplet capture and release, minimizing size variability. Additionally, the injection rate plays a critical role in CO2 sequestration, with higher rates promoting convective mixing between CO2 and reservoir fluids, thereby enhancing dissolution and storage efficiency. The complexity of the pore structure, characterized by the presence of micropores and macropores, affects the dissolution kinetics and mobility of CO2, influencing sequestration efficiency. These experimental findings provide valuable insights into the dynamics of oil–water motion and the potential for enhanced oil recovery (EOR) and CO2 storage, offering essential guidance for optimizing CWI strategies in the petroleum industry.

Research and Practice of Development Model during the Continental Heavy Oil Field’s Extra-high Water Cut Stage in the Bohai Sea

Abstract The formation mechanism, production limits and injection-production pattern of residual oil were studied by laboratory experiment, micropore simulation and reservoir engineering. The findings indicate that when injection times increase, the displacement efficiency rises as well. The residual oil mostly remains in the pore throat, which has a radius of 10 to 50 μ m, with a mean pore throat radius of 35 μ m.. As the displacement pressure gradient increases from 0.004MPa/m to 0.012MPa/m, When the displacement ratio of piston type increases and the displacement ratio of water film flow drops, the displacement efficiency grows. The horizontal well pattern’s gradient of displacement pressure is increased by 1.5 ~ 1.7 times compared with the oriented well pattern, and the displacement efficiency is increased by 12% ~ 15%. The development of the Bohai oilfield during the ultra-high water cut stage has been informed by the aforementioned findings, forming a horizontal well joint directional well three-dimensional pattern development model, oil production rate increased from 1.3% to 2.3%, and water drive recovery rate increased from 24.5% to 38.6%, realizing efficient development in the ultra-high water cut stage, and providing reference for the development of similar oil fields.

Pore-scale study of three-dimensional three-phase dynamic behaviors and displacement processes in porous media

Carbon dioxide geological sequestration is a key method to alleviate global warming and enhance oil recovery, where the three-phase displacement processes of oil, water, and carbon dioxide gas in porous media are frequently encountered. In this study, a three-phase three-dimensional lattice Boltzmann method coupled with special wettability and outlet boundary schemes is adopted to simulate the three-phase displacement processes in porous media. The method is validated by the contact angles on a curved surface and droplet flowing through the outlet boundary. With this method, the influences of capillary number, wettability, and local large pores on three-phase flow are investigated. In particular, different dynamic behaviors of fluids are observed at the pore scale, such as bypass-double displacement, stop-wait displacement, burst displacement, snap-off trapping, and corner flow. Further, Euler number and oil saturation are calculated to quantitatively characterize the fluidic morphology and displacement efficiency under different conditions. For all three phases, the Euler number of low capillary number, strong water-wet, and structures with large and medium pores is relatively low, indicating that the morphology of fluids is more connective. For enhancing oil recovery efficiency, high capillary number and strong water-wet structures are beneficial.

Non-thermal recovery of a viscous oil with a surfactant-polymer process

The goal of this work is to improve recovery of a viscous oil reservoir at 70 °C using a non-thermal process. Polymer floods can improve sweep efficiency, but leave behind a residual oil saturation. A surfactant-polymer flood has the potential to improve both the sweep as well as the displacement efficiency. Phase behavior experiments with the viscous oil, water and surfactants were conducted to identify surfactants. 1D and 2D sandpack displacements were conducted to evaluate the efficacy of the process. Phase behavior experiments showed Winsor type I behavior with a low interfacial tension using a single surfactant, but not ultralow tension. Water flood recovered about 50% OOIP and reduced the oil saturation to about 45% in 1D floods. The subsequent SP flood increased the cumulative oil recovery to 99% in sandpacks when the viscosity of chemical slugs exceeded the oil viscosity. When the permeability decreased (as in a Bentheimer core), the oil recovery decreased to about 86%. Secondary SP floods also recovered most of the oil and faster than tertiary floods. Reduction of polymer concentration (and viscosity to about 1/4th of the oil viscosity) reduced the oil recovery, especially in 2D sandpack floods. Decrease in interfacial tension increased the requirement of polymer concentration to maintain flood front stability. This flood demonstrates the effectiveness of Winsor type I SP formulation for viscous oil, high permeability reservoirs. Such a SP process would reduce the carbon footprint of viscous oil recovery compared to that of thermal processes.

Immiscible non-Newtonian displacement flows in stationary and axially rotating pipes

We examine immiscible displacement flows in stationary and rotating pipes, at a fixed inclination angle in a density-unstable configuration, using a viscoplastic fluid to displace a less viscous Newtonian fluid. We employ non-intrusive experimental methods, such as camera imaging, planar laser-induced fluorescence (PLIF), and ultrasound Doppler velocimetry (UDV). We analyze the impact of key dimensionless numbers, including the imposed Reynolds numbers (Re, Re*), rotational Reynolds number (Rer), capillary number (Ca), and viscosity ratio (M), on flow patterns, regime classifications, regime transition boundaries, interfacial instabilities, and displacement efficiency. Our experiments demonstrate distinct immiscible displacement flow patterns in stationary and rotating pipes. In stationary pipes, heavier fluids slump underneath lighter ones, resulting in lift-head and wavy interface stratified flows, driven by gravity. Decreasing M slows the interface evolution and reduces its front velocity, while increasing Re* shortens the thin layer of the interface tail. In rotating pipes, the interplay between viscous, rotational, and capillary forces generates swirling slug flows with stable, elongated, and chaotic sub-regimes. Progressively, decreasing M leads to swirling dispersed droplet flow, swirling fragmented flow, and, eventually, swirling bulk flow. The interface dynamics, such as wave formations and velocity profiles, is influenced by rotational forces and inertial effects, with Fourier analysis showing the dependence of the interfacial front velocity's dominant frequency on Re and Rer. Finally, UDV measurements reveal the existence/absence of countercurrent flows in stationary/rotating pipes, while PLIF results provide further insight into droplet formation and concentration field behavior at the pipe center plane.

Research on the Mechanism of Nanoparticle materials in Oil Displacement and its Application

Abstract The application of nanoparticles in the field for enhanced oil recovery (EOR) is a new technology, which has attracted widespread concern. However, there is a lack of systematic research on the types and mechanisms. In order to clarify the types and characteristics of the material, oil displacement mechanism and its effect on oil and water flow, this paper systematically sorted out the classification of nanoparticle materials used in the field of petroleum development, and analysed its percolation and oil displacement mechanism. Numerical simulation and field data analysis were carried out to study the applications of two types of nanomaterials in improving reservoir water injection and oil displacement efficiency quantitatively. The results show that the main mechanism of nanoparticle flooding is to change reservoir wettability, reduce oil-water interfacial tension, modify the mobility ratio between water and oil phases, and reduce asphaltene precipitation. Lipophilic and hydrophobic nanoparticle may reduce injection pressure, and increases significantly injection in low permeability reservoirs, and the average water injectability of 6 wells is increased by 177.76%. The displacement efficiency of hydrophilic and oleophobic nanoparticles can be increased by 14.78%. This paper reveals the oil displacement mechanism of nanoparticle materials and establishes a new method to quantitatively predict the oil displacement effect of nanoparticle materials, which provides a basis and reference for the application of oilfield.

تصميم نظام غمر المياه لحقل الدفا النفطي

Currently, water-flooding is responsible for a big portion of world oil production. The vertical sweep efficiency and the areal coverage each of these requires careful sampling to get represented reservoir rock and fluid properties measures of reservoir heterogeneity, Economically, a pilot is a desirable tool for studying oil recovery performance on reservoir sample and then scaled up to yield the performance to be expected from field performance. Defa field was produced since 1968 with good oil flow rate reaching 200,000 BOPD but during the life of the field, the production decreased to 50,000 BOPD in 2001. So, this study was conducted to increase oil production by add some energy to the reservoir to increase average reservoir pressure and try to maintain it to initial pressure and to increase displacement and sweep efficiency. The water flooding design was implemented in sector model in the Defa field using five spots pattern. The study was performed by using Excel and Water Drive software to achieve a good water flooding design. When comparing the results obtained from two calculation methods, the minimum error was equal 0.03 percent and the maximum error was around 12 percent. So, the results were acceptable and the process was recommended to the Defa-field. Keywords: Water flooding; Software; Fractional Flow, Break through.

Investigation the Impact of Different Injection Agents on Tight Oil Reservoirs of Recovery Performance

Abstract Objectives/Scope: Due to strong water sensitivity and extremely low permeability, conventional water flooding method is not suitable for the Mahu Conglomerate reservoir. In response to the complex reservoir physical properties, different injection agents such as CO2, N2, water and air huff and puff injection were carried out in order to optimize injection parameters for enhanced oil recovery in tight conglomerate reservoirs. Methods, Procedures, Process: By means of NMR, scanning electron microscopy, energy spectrum, pore fluids state in different media after different agents displacement were studied. Displacement and CT testing on different media and post fracturing state were conducted. Through experiments on on-site cores from two different layers, three different injection media (H2O, N2, CO2 and air with different O2 concentration) were tested for enhanced oil recovery. Then, the injection process was performed under different injection pressures. Finally, multiple cycles of enhanced oil recovery tests were conducted corresponding optimal injection pressures. Results, Observations, Conclusions: The remaining oil in the pores is mainly in free and bound states, with a free state of approximately 58% and a bound state of approximately 42%. Four pressures were selected for this test based on the minimum miscibility pressure of CO2 with crude oil: 15MPa, 20MPa, 23MPa, and 25MPa. The recovery factor under different pressures is 6.44%, 8.14%, 10.31%, and 10.38%, respectively. As the huff and puff pressure increases, the recovery of CO2 huff and puff gradually increases, and the increase of recovery is insignificant when the mixture pressure is reached. The gas flooding process involves oil production from large and submicron pores first. As the displacement pressure difference increases, oil production from large pores decreases, with medium pores becoming the main force of oil production, while oil production from nanoscale micropores shows an increasing trend. The increase in oxygen content results in significant development of sub-micron micron scale pores. The gas breakthrough time is long, the capillary force decreases, and air can undergo low-temperature oxidation with crude oil, resulting in an overall oil displacement efficiency of 65.81%. Novel/Additive Information: At present, there is few research on the pore fluid flow and status of oil displacement in tight conglomerate reservoirs with different injection media. This study provides a good understanding of the submicron to nanoscale pore throat structure characteristics of tight oil reservoirs, revealing the state of pore fluids in gravel after displacement by different injection media, and providing support for on-site application of CO2 enhanced oil recovery in tight conglomerate oil reservoirs.

Three dimensional time-variation simulator for water flooding reservoir based on “effective water flux”

Long-term water flooding leads to changes in pore throat structure, resulting in alterations in macroscopic reservoir petrophysical parameters. However, commercial numerical simulation software does not have this capability. Ignoring variations in physical parameters during the formulation of development plans and numerical simulations can lead to significant prediction errors, which severely impacts oil field recovery. This paper, based on an analysis of effective flow rate and waterflood intensity, proposes a new erosion degree characterization parameter: Effective water flux, to represent the time-varying patterns of physical parameters. It is embedded into a black oil model to develop a time-variation simulator, whose accuracy and stability in both black oil and time-variation models are validated through comparison with the commercial numerical simulation software CMG. The study further explores the effects of different parameter variations on the development process. It was found that increases in permeability and oil viscosity exacerbate heterogeneity and reduce displacement efficiency, while decreases in residual oil saturation and water phase permeability under residual oil saturation enhance water flooding efficiency. In complex models, the effects of variations in different parameters intertwine, collectively influencing development outcomes. This paper advances the development of time-variation numerical simulation technology.

Experimental Study on Factors Influencing the Efficiency of Hot Water Injection in Offshore Heavy Oil Reservoirs

Abstract In response to the problem of low final recovery rate in conventional water flooding development of offshore heavy oil, the Bohai LD5 heavy oil field was taken as the target area. Through one-dimensional oil displacement efficiency experiments, the influence of crucial injection and production parameters on oil displacement efficiency, such as temperature, injection rate, injection production ratio, timing of hot water flooding, and injection medium, was studied. The key injection and production parameters were optimized, and the main controlling factors affecting the efficiency of hot water flooding after water flooding were identified through data analysis. Propose an optimization approach for thermal injection media and quantitatively evaluate the oil recovery efficiency under different injection and production parameters. Research has shown that for the Bohai LD5 heavy oil field, the optimal combination of injection and production parameters is: an injection rate of 2mL/min, injection temperature of 110°C, and timing of conversion to flooding at a recovery rate of 20% to 30% (water content of 55% to 70%). The hot water composite flue gas has the best oil recovery effect, considering both oil recovery efficiency and on-site construction conditions. The degree of influence of various factors on the efficiency of hot water flooding is as follows: temperature>timing of hot water flooding (recovery degree)>injection rate. Under low temperature (within 110 °C) conditions, temperature is the main factor affecting the efficiency of hot water flooding. The overall recovery rate of different injection media shows a trend of hot water composite>hot water>cold recovery.

Why gravity improves waterflood recovery in oil-wet and mixed-wet reservoirs

Most past experimental and numerical research on water flooding has demonstrated a reduction in oil recovery in gravity dominated flow: gravity leads to the water slumping to the bottom of the reservoir with earlier water breakthrough and poor sweep efficiency. However, these studies were all performed on strongly water-wet systems: wherever the water has gone, the oil is at residual saturation so a reduction in sweep efficiency gives a reduction in recovery. In reality few if any reservoirs are strongly water-wet. If the rock is mixed or oil-wet, gravity improves the local displacement efficiency. Gravity reduces the mobility of injected water forcing downward water movement and better oil displacement laterally. When gravity dominates, once water reaches the bottom of the reservoir, it moves upwards in a gravity-stable displacement, with improved local displacement efficiency that can be quantified by linear Buckley-Leverett analysis. We show, using fine-grid simulations of water flooding in a two-dimensional homogeneous vertical cross-section with typical fluid and rock properties, that the overall recovery after ∼0.3 pore volumes of water injected is higher than without gravity for heavy oil-wet (unfavourable mobility) applications. This improvement is greater in light oil-wet (favourable mobility) applications and occurs even before water breakthrough counteracting the negative effect of poor sweep efficiency. Simulations on a heterogeneous reservoir model representing an oil field from the Middle East confirmed the significance of gravity on improving the displacement and overall oil recovery. The same considerations should pertain in reverse for gas storage: storage efficiency improves in gravity dominated flow.

Study on Variability Production Characteristics of Fracturing Fluid Imbibition Displacement for Typical Shale

Abstract CO2 injection is a prominent measurement to enhance the recovery of shale reservoirs. The imbibition of fracturing fluid + CO2 additive is considered important for promoting the enhancement and stabilization of shale oil production to ensure energy supply. The imbibition experiments of fracturing fluid + CO2 additive were carried out in shale reservoirs with a nuclear magnetic resonance (NMR) test. The imbibition displacement characteristics at different pore scales of shale were quantitatively evaluated. The variability of the imbibition effects in shale reservoirs was clarified in terms of shale type, fracturing fluid type, and CO2 additive (pressure). This finding indicates that the effectiveness of the fracturing fluid + CO2 additive imbibition on shale reservoirs is stronger, and the imbibition displacement efficiency ranges from 33.38 % to 41.56 %. The imbibition contribution rate is considerably higher for small pores than for large pores, and the difference between them is more than 10%. Therefore, the imbibition of fracturing fluid + CO2 additive mainly extracted crude oil from the small pores of shale reservoirs. CNI nano variable-viscous slippery water is more effective for imbibition displacement in laminar type shale. For laminated type shale, EM30+ + guanidine gum mixed water has a better imbibition effect than CNI nano variable-viscous slippery water. Under 16 MPa CO2 + fracturing fluid (miscible states), the imbibition displacement efficiency of the shale is significantly enhanced. The imbibition displacement degree at different pore scales is also increased. For different types of shale reservoirs, the imbibition displacement degree at different pore scales would be improved by methods, including the optimization of the fracturing fluid or the change of imbibition conditions. This study presents a theoretical underpinning for the high-efficiency exploitation in shale reservoirs.

Two-Dimensional Physical Model Experimental Study on Sweep Efficiency of Offshore Heavy Oil Hot Water Flooding

Abstract The conventional water flooding approach for the development of ordinary heavy oil faces challenges such as high injection-production mobility, rapid increase in water cut, and low final recovery. By using the temperature-sensitive properties of heavy oil, the viscosity can be effectively reduced, and the flow capacity within porous media can be enhanced by increasing the temperature of injected water. Onshore hot water flooding is primarily used to exploit the remaining oil potential during the later stages of steam stimulation, while offshore is used to enhance efficiency during the mid to late stages of water flooding. The key to the success of hot water flooding technology lies in the improvement of the sweep coefficient. Firstly, a two-dimensional physical experiment model is designed in accordance with the geological and reservoir characteristics of the target oilfield, based on the principle of similarity. Secondly, parameters that quantitatively characterize the development law of the plane temperature field, such as the effective sweep coefficient, regular factor, and plane expansion speed of the high-temperature region, are studied. Then, through two-dimensional experiments, the effects of injection medium, formation rhythm, and timing of hot water injection on sweep efficiency and temperature field development were discussed. Finally, on the basis of two-dimensional experiments, the effects of heat injection temperature, timing of heat injection, hot water injection speed, and high permeability strip on the improvement of sweep efficiency were quantitatively analyzed by numerical simulation. The results show that compared with hot water flooding, hot water composite flooding can increase the effective sweep coefficient from 15.05 % to 28.71 %. The anti-rhythm is helpful to the upward expansion of the high temperature zone, which can increase the oil displacement efficiency by 1.5 %. Water channeling can be effectively controlled by injecting hot water with low water cut. The increase of heat injection temperature is helpful to increase the proportion of high temperature heating area. The higher the injection speed, the greater the expansion speed of the heating chamber. The research results provide a direction for the development of heavy oil conventional water flooding to improve oil recovery in offshore heavy oil.

Pore-Scale Mechanism Analysis of Enhanced Oil Recovery by Horizontal Well, Dissolver, Nitrogen, and Steam Combined Flooding in Reducer Systems with Different Viscosities for Heavy Oil Thermal Recovery

Horizontal well, dissolver, nitrogen, and steam (HDNS) combined flooding is mainly applied to shallow and thin heavy oil reservoirs to enhance oil recovery. Due to the lack of pore-scale mechanism studies, it is impossible to clarify the oil displacement mechanism of each slug in the process combination and the influence of their interaction on enhanced oil recovery (EOR). Therefore, in this study, HDNS combined flooding technology was simulated in a two-dimensional visualization microscopic model, and three viscosity reducer systems and multi-cycle combined flooding processes were considered. In combination with an emulsification and viscosity reduction experiment, two-dimensional microscopic multiphase seepage experiments were carried out to compare the dynamic seepage law and microscopic occurrence state of multiphase fluids in different systems. The results showed that the ability of three viscosity reducers to improve viscosity reduction efficiency in HDNS combined flooding was A > B > C, and their contributions to the recovery reached 65%, 41%, and 30%, respectively. In the system where a high viscosity reduction efficiency was shown by the viscosity reducer, the enhancements of both sweeping efficiency and displacement efficiency were primarily influenced by the viscosity reducer flooding. Steam flooding collaborated to improve displacement efficiency. The thermal insulation characteristics of N2 flooding may not provide a gain effect. In the system where a low viscosity reduction efficiency was shown by the viscosity reducer, the steam flooding was more important, contributing to 57% of the sweeping efficiency. Nitrogen was helpful for expanding the sweep area of the subsequent steam and viscosity reducer, and the gain effect of the thermal insulation steam chamber significantly improved the displacement efficiency of the subsequent steam flooding by 25%. The interaction of each slug in HDNS combined flooding resulted in the additive effect of increasing production. In actual production, it is necessary to optimize the process and screen the viscosity reducer according to the actual conditions of the reservoir and the characteristics of different viscosity reducers.