Reservoir Flood Research Articles

Experimental Study on Early Polymer Injection Timing of Heavy Oil Reservoir in Bohai Sea

The polymer flooding of ordinary heavy oil reservoirs in Bohai Sea can improve the crude oil recovery by advancing the injection time of polymer flooding. The better the injection time is, the higher the enhanced recovery is, and the greater the income is. Based on Bohai Oilfield, the polymer application system was characterized in the laboratory, and then polymer flooding experiments were carried out at different times using one-dimensional core model. The results show that: 1) polymer AP-P4 can establish good mobility control ability (RF=107, RRF=28.5) under the target reservoir conditions; 2) Under the experimental conditions, the best time for polymer injection is to switch to polymer injection after 0.203PV water injection, and the oil recovery can be increased by 27.73%. Early polymer injection technology is very beneficial to polymer flooding in offshore oil fields.

Study on the mechanism of CO2 injection to improve tight sandstone gas recovery

Supercritical CO2 can improve gas recovery and achieve carbon sequestration in tight gas reservoir. It is a hot topic but not applied extensively. The main restricts include the unclear mechanism of gas-to-gas displacement and the reduction of the natural gas asset value due to CO2 breakthrough. In this paper, a novel experimental method is used, through constant-volume and constant-pressure experiments, to analyze the mixing process of CO2 and natural gas in different parts of vessel. Moreover, the mechanism and impact factors of natural gas displaced by supercritical CO2 are demonstrated in laboratory and numerical simulation. Based on the experiments, the diffusion coefficient of CO2 in natural gas (CH4) is measured and input into the numerical model. The results show that supercritical CO2 in the reservoir is ‘partially miscible’ with the natural gas. CO2 displaces CH4 to move upward due to the gravity differentiation, and CH4 is produced in the process of CO2-subsidence. CO2 flooding can enhance gas recovery by 18%, which verifies the technical feasibility of CO2 flooding in tight gas reservoirs.

Investigation of feasibility of alkali–cosolvent flooding in heavy oil reservoirs

Cold production is a challenge in the case of heavy oil because of its high viscosity and poor fluidity in reservoir conditions. Alkali–cosolvent–polymer flooding is a type of microemulsion flooding with low costs and possible potential for heavy oil reservoirs. However, the addition of polymer may cause problems with injection in the case of highly viscous oil. Hence, in this study the feasibility of alkali–cosolvent (AC) flooding in heavy oil reservoirs was investigated via several groups of experiments. The interfacial tension between various AC formulations and heavy crude oil was measured to select appropriate formulations. Phase behavior tests were performed to determine the most appropriate formulation and conditions for the generation of a microemulsion. Sandpack flooding experiments were carried out to investigate the displacement efficiency of the selected AC formulation. The results showed that the interfacial tension between an AC formulation and heavy oil could be reduced to below 10−3 mN/m but differed greatly between different types of cosolvent. A butanol random polyether series displayed good performance in reducing the water–oil interfacial tension, which made it possible to form a Type III microemulsion in reservoir conditions. According to the results of the phase behavior tests, the optimal salinity for different formulations with four cosolvent concentrations (0.5 wt%, 1 wt%, 2 wt%, and 3 wt%) was 4000, 8000, 14000, and 20000 ppm, respectively. The results of rheological measurements showed that Type III microemulsion had a viscosity that was ten times that of water. The results of sandpack flooding experiments showed that, in comparison with waterflooding, the injection of a certain AC formulation slug could reduce the injection pressure. The pressure gradient during waterflooding and AC flooding was around 870 and 30–57 kPa/m, respectively. With the addition of an AC slug, the displacement efficiency was 30%–50% higher than in the case of waterflooding.

Utilization mechanism of foam flooding and distribution situation of residual oil in fractured-vuggy carbonate reservoirs

The development of fractured-vuggy carbonate reservoirs is extremely difficult because of the complex fractured-vuggy structure and strong heterogeneity. Foam flooding is a potential enhanced oil recovery (EOR) technology in fractured-vuggy carbonate reservoirs. Based on the similarity criterion, three types of 2D visual physical models of the fractured-vuggy structure were made by laser ablation technique, and a 3D visual physical model of the fractured-vuggy reservoir was made by 3D printing technology. Then the physical analog experiments of foam flooding were carried out in these models. The experimental results show that foam can effectively improve the mobility ratio, control the flow velocity of the fluid in different directions, and sweep complex fracture networks. The effect of foam flooding in fractures can be improved by increasing foam strength and enhancing foam stability. The effect of foam flooding in vugs can be improved by reducing the density of the foam and the interfacial tension between foam and oil. Three types of microscopic residual oil and three types of macroscopic residual oil can be displaced by foam flooding. This study verifies the EOR of foam flooding in the fractured-vuggy reservoir and provides theoretical support for the application of foam flooding in fractured-vuggy reservoirs.

Remote Sensing-Supported Flood Forecasting of Urbanized Watersheds—A Case Study in Southern China

Urbanization has significant impacts on watershed hydrology, but previous studies have been confirmatory and not comprehensive; in particular, few studies have addressed the impact of urbanization on flooding in highly urbanized watersheds. In this study, this effect is studied in Chebei Creek, a highly urbanized watershed in the Pearl River Delta, southern China. Landsat satellite images acquired in 2015 were used to estimate land use and cover changes using the Decision Tree (DT) C4.5 classification algorithm, while the Liuxihe model, a physically based distributed hydrological model (PBDHM), is employed to simulate watershed flooding and hydrological processes. For areas with high degrees of urbanization, the duration of the flood peak is only 1 h, and the flood water level shows steep rises and falls. These characteristics increase the difficulty of flood modeling and forecasting in urbanized areas. At present, hydrological research in urbanized watersheds generally focuses on the quantitative simulation of runoff from urban areas to the watershed, flood flows, peak flood flow, and runoff depth. Few studies have involved real-time flood forecasting in urbanized watersheds. To achieve real-time flood forecasting in urbanized watersheds, PBDHMs and refined underlying surface data based on remote sensing technology are necessary. The Liuxihe model is a PBDHM that can meet the accuracy requirements of inflow flood forecasting for reservoir flood control operations. The accuracies of the two flood forecasting methods used in this study were 83.95% and 97.06%, showing the excellent performance of the Liuxihe model for the real-time flood forecasting of urbanized rivers such as the Chebei Creek watershed.

Evaluation of modified cashew nutshell liquid as natural surfactants for chemical flooding in sandstone oil reservoirs

Bio-based oilfield chemicals are gaining attention due to their availability, cost-effectiveness, and non-toxic nature. Surfactants facilitate recovery of residual oil by reducing the interfacial tension between two immiscible fluids. Cashew nutshell liquid (CNSL) extracted from Anacardium occidentale waste shells was modified using triethanolamine and evaluated as a natural alternative to traditional surfactants. Phase behavior analysis, interfacial tension, critical micelle concentration (CMC) measurements, and core flooding analysis were performed to ascertain the compatibility and recoverability of the cashew nutshell liquid derivatives on sandstone reservoirs. Interfacial tension was reduced from 10.46 to 1.66 mN/m at CMC of 1 g/L. Additional recovery factor and displacement efficiency of 12% OOIP and 32.5%, respectively, was achieved at laboratory temperature. The effect of temperature on residual oil recovery was determined by subjecting the oil displacement experiment to reservoir temperature of 80˚C, resulting in recovery factor and displacement efficiency of 9% OOIP and 25%, respectively.

Multi-point resistivity measurement system for full-diameter long cores during fluid displacement.

Water injection is often used to improve oil and gas recovery in the late stage of oil and gas reservoir development. Studies show that this process leads to complex changes in reservoir resistivity and affects the evaluation of remaining oil and gas saturation in the reservoir. In this study, a multi-point resistivity measurement experimental system suitable for full-diameter rock samples during fluid displacement was designed to simulate and explore the distribution and variation of resistivity in the reservoir flooding process. In this regard, two columnar electrodes were installed on the end face of the core sample to serve as fluid injection and outflow channels. Moreover, five groups of nail-shaped electrodes arranged at equal intervals were embedded on the rubber sleeve of the core holder. The electrical bridge metering combined with seven electrodes was used to measure the resistivity and variation of six parts of the core sample during fluid displacement. A confining pressure was applied to the core sample to simulate the underground high-pressure environment and force the nail-shaped electrodes to cling to the sample to improve the accuracy of resistivity measurement. The simulated water flooding experiment was carried out with a sandstone sample from Tarim Oilfield in western China, and the distribution and variation of the sample's resistivity were recorded. The experimental results conform to the laws of rock physics and confirm the reliability of the experimental system. The experimental system provides a guideline for determining the resistivity variation and evaluating the remaining oil and gas saturation of water-flooded reservoirs.

Displacement efficiency and storage characteristics of CO2 in low permeability reservoirs: An experimental work

Over the past decades, CO2 flooding in low-permeability porous media has continued to grow. Furthermore, propelled by the current movement toward CO2 sequestration, the flooding of CO2 is expected to further increase. Thus, it is of scientific significance to study the mechanism of displacement of CO2 flooding as well as the CO2 storage characteristics. In this study, CO2 miscible/immiscible flooding experiments were conducted on two low permeability samples to study the difference between them. Specifically, the effect of oil displacement and CO2 storage coefficient for different displacement models were measured and compared. In addition, nuclear magnetic resonance (NMR) tests and frozen pelleting experiments were conducted. The NMR tests clarified the lower limit of pore throat where oil can be displaced by CO2 miscible/immiscible flooding. Furthermore, the frozen pelleting experiments analyzed the distribution characteristics of the remaining oil before and after CO2 miscible/immiscible flooding. The investigation showed that the development efficiency of CO2 miscible flooding is higher than CO2 immiscible flooding in low permeability reservoirs. The results also indicated that CO2 miscible flooding increases the recovery of hard-to-produce semi-bound oil phase and CO2 storage coefficient with CO2 miscible displacement is more significant than that with CO2 immiscible flooding. The data from this study is a critical input for reservoir simulation, which sheds light on the CO2 miscible/immiscible flooding in low permeability reservoirs.

Laboratory Investigation of Nanofluid-Assisted Polymer Flooding in Carbonate Reservoirs

In the petroleum industry, the remaining oil is often extracted using conventional chemical enhanced oil recovery (EOR) techniques, such as polymer flooding. Nanoparticles have also greatly aided EOR, with benefits like wettability alteration and improvements in fluid properties that lead to better oil mobility. However, silica nanoparticles combined with polymers like hydrolyzed polyacrylamide (HPAM) improve polymer flooding performance with better mobility control. The oil displacement and the interaction between the rock and polymer solution are both influenced by this hybrid approach. In this study, we investigated the effectiveness of the injection of nanofluid-polymer as an EOR approach. It has been observed that nanoparticles can change rock wettability, increase polymer viscosity, and decrease polymer retention in carbonate rock. The optimum concentrations for hydrolyzed polyacrylamide (2000 ppm) and 0.1 wt% (1000 ppm) silica nanoparticles were determined through rheology experiments and contact angle measurements. The results of the contact angle measurements revealed that 0.1 wt% silica nanofluid alters the contact angle by 45.6°. The nano-silica/polymer solution resulted in a higher viscosity than the pure polymer solution as measured by rheology experiments. A series of flooding experiments were conducted on oil-wet carbonate core samples in tertiary recovery mode. The maximum incremental oil recovery of 26.88% was obtained by injecting silica nanofluid followed by a nanofluid-assisted polymer solution as an EOR technique. The application of this research will provide new opportunities for hybrid EOR techniques in maximizing oil production from depleted high-temperature and high-salinity carbonate reservoirs.

Probing the Effect and Mechanism of Flue Gas on the Performance of Resorcinol/Hexamethylenetetramine-Based Polymer Gel in Flue Gas Flooding Reservoir.

Polymer gel plugging is an effective method for gas mobility control in flue gas flooding reservoirs. However, the effect and mechanism of flue gas on the performance of polymer gels have rarely been reported. In this study, a polymer gel was prepared by cross-linking hydrolyzed polyacrylamide (HPAM) and resorcinol/ hexamethylenetetramine (HMTA) to illuminate the influencing mechanism of flue gas composition on gel. The gel rheological testing results showed that flue gas promoted gelation performance, whereas it seriously threatened gel long-term stability, especially at high pressure conditions. The influence of CO2 on the polymer gel had the characteristic of multiplicity. The hydrodynamic radius (Rh) and the initial viscosity of HPAM solution decreased in the presence of CO2. Nonetheless, the dissolved CO2 expedited the decomposition rate of HMTA into formaldehyde, which promoted the cross-linking process of the HPAM, leading to a shorter gelation time. Oxidation-reduction potential (ORP) tests and Fourier transform infrared spectroscopy (FTIR) analysis indicated that O2 played a leading role in the oxidative degradation of HPAM compared to CO2 and threatened the gel long-term stability at elevated gas pressures. To address the adverse effects caused by flue gas, it is highly desirable to develop polymer gels by adding oxygen scavengers or strengthening additives.

An Analytical Framework for Investigating Trade-Offs between Reservoir Power Generation and Flood Risk

Converting floodwater into power without increasing flood risk is critical for energy-stressed regions. Over the past decades, numerous methods have been proposed to solve this problem. However, few studies have investigated the theoretical explanation of the trade-offs between power generation and flood risk. This study establishes an analytical framework to derive optimal hedging rules (OHR) and explains the economic insights into flood risk reduction and power generation improvement. A two-stage model based on the concept of dynamic control of carryover storage (DCCS) was developed as part of the framework, considering forecast uncertainty and risk tolerance. The results illustrated that hedging and trade-offs between power generation and flood risk during DCCS only occurs when the forecasted inflow and forecast uncertainty are within certain ranges, beyond which there is no hedging and trade-offs analysis; either power generation or flood risk becomes the dominant objective. The OHR was divided into three cases under different levels of forecast uncertainty and risk tolerance. Compared to forecast uncertainty, downstream risk tolerance plays a more important role in determining which case of the OHR is adopted in real-world operations. The analysis revealed what and how intense trade-offs are between power generation and flood risk under different scenarios of forecasted inflow, forecast uncertainty, and risk tolerance. The framework serves as a guideline for less abundant water resources or energy-stressed areas of operational policy. Nierji Reservoir (located in northeast China) was taken as a case study to illustrate the analysis, and the application results showed that OHR increases the average annual power generation by 4.09% without extra flood risk compared to current operation rules.

Laboratory evaluation of red onion skin extract and its derivative as biomass-based enhanced oil recovery agents

The use of natural alternatives as oilfield chemicals is gradually gaining attention among researchers due to their eco-friendly nature. The aim of this study was to determine the efficiency of red onion skin extract (ROSE) at recovering residual oil using the mechanism of surfactant flooding in sandstone reservoirs at reservoir conditions and compare its effectiveness in its pristine and modified state. ROSE was obtained by solvent extraction of the waste biomass (red onion skin) using acetone. The extract was chemically modified using glutaraldehyde. Phase behavior analysis in the presence of divalent ions at high temperatures (80 ˚C) and sandstone core flooding were performed to determine the fluid compatibility and displacement efficiency. Results show high compatibility and solubility of pristine (unmodified) and modified ROSE in soft and hard brine. Core flooding analysis showed a higher recovery of 32.1% and 36.5% original oil in place (OOIP) for 0.3 wt.% modified ROSE as compared to a recovery factor of 31.8% and 35.0 % OOIP for 0.5% unmodified ROSE in soft and hard brine respectively. It further reveals an increase in additional recovery at surfactant concentration in hard brine above critical micelle concentration (CMC). Results of statistical significance test showed that modified ROSE exhibited superior performance and a higher recovery relative to unmodified ROSE especially in hard brine. This is a novel work as red onion skin extract was derivatized with glutaraldehyde and successfully recovered additional residual oil under hard brine and reservoir temperature making them potential surface-active agents for chemical enhanced oil recovery.

Low salinity water and polymer flooding in sandstone reservoirs: Upscaling from nano-to macro-scale using the maximum energy barrier

In this work, the flooding processes of low salinity waterflooding and low salinity polymer flooding (LSWF and LSP) in sandstone reservoirs were mechanistically modelled at nano-and macro-scales. Triple-layer surface complexation models were utilised to simulate interactions at the oil-brine and sandstone-brine interfaces. The Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was applied to describe the stability of interfacial films in crude oil-brine-sandstone rock systems. The novel application of the maximum energy barrier (MEB), calculated from the interaction potential of the DLVO theory, as an upscaling and interpolant parameter to adjust relative permeability curves as a function of reservoir properties is proposed in this work. Numerical simulations using the commercial simulator CMG-STARS were used in tandem with the surface complexation models and film analysis to evaluate the performance of LSWF and LSP in sandstone reservoirs.Results of the numerical simulations showed that the LSP gave significantly higher oil recovery compared to standard polymer flooding because of its utilisation of wettability alteration due to LSWF and the improved mobility control due to LSP. A comparison between studied injection processes i.e. low and high salinity waterflooding, and low and high salinity polymer flooding, revealed that oil recovery as a result of wettability alteration is significantly higher than that of mobility control. Further analysis indicated that temperature affects the wettability alteration favourably, and the polymer slug viscosity unfavourably. However, the temperature effect on the wettability was found to be more pronounced. The workflow presented in this study provides valuable guidelines in screening the appropriate sandstone reservoirs for LSWF and LSP applications using the numerical simulation techniques through the upscaling from nano-to-macro-to-field scale.

A surrogate assisted evolutionary multitasking optimization algorithm

Evolutionary algorithms (EAs) have been applied with strong abilities to solve a wide range of applications, but it can solve one problem at a time. To improve efficiency, an emerging research paradigm in the field of evolutionary computation, Evolutionary multi-tasking (EMT) was proposed. EMT solves multiple optimization tasks simultaneously. The effectiveness of EMT is to improve the solutions for each task via inter-task knowledge transfer. Multifactorial evolutionary algorithms (MFEAs) is the first algorithm proposed to solve multi-task optimization problems. However, it tends to suffer from the issue of negative knowledge transfer. To address this issue and improve the performance of MFEA, we propose to construct a surrogate model as a helper task is optimized and target task simultaneously in MFEA. According to the proposed method, the surrogate model is a related task for each corresponding target task to enhance positive inter-task knowledge transfer. Besides, the surrogate model can reduce the number of local optima and has a simple structure. Experiments are conducted on benchmarks and real-world reservoir flood generation power problems to examine the performance of the proposed algorithm. Comparative experiments on several widely used test problems demonstrated that surrogate models as helper tasks enable significantly improve the performance of MFEA.

Application Research of CFD-MOEA/D Optimization Algorithm in Large-Scale Reservoir Flood Control Scheduling

Reservoir flood control has an important impact on flood protection and plays an important role in reducing the loss of people’s lives and property. In order to play an important role in flood control operation of large-scale reservoirs, a control flood dispatching multi-objective evolutionary algorithm based on decomposition (CFD-MOEA/D) is proposed. The same type of multi-objective optimization algorithm (non-dominated sorting genetic algorithm II (NSGA-II)) is introduced, and CFD-MOEA/D, NSGA-II, and traditional MOEA/D algorithms are compared. The research results show that the CFD-MOEA/D algorithm can obtain the non-dominated solution of the higher water level in the upstream, and the solution obtained by the CFD-MOEA/D algorithm is more sufficient than the NSGA-II algorithm and the MOEA/D algorithm. When analyzing the HV value curve, the uniformity and convergence of the optimal solution obtained by the CFD-MOEA/D algorithm are better than those of the other two algorithms. The optimal dispatching scheme of the CFD-MOEA/D algorithm is compared with the actual dispatching scheme of the reservoir, and it is found that the maximum upstream water level and the final water level obtained by the CFD-MOEA/D algorithm are both kept at approximately 325 m, which is consistent with the actual dispatching scheme. The new feature of the algorithm is that it uses a decomposition method from coarse to fine and improves the hourly scheduling scheme to obtain higher scheduling efficiency.

Deriving optimal operating rules for flood control considering pre-release based on forecast information

Pre-releasing before a flood can increase reservoir flood control storage capacity to effectively improve the flood disaster prevention and mitigation effects, but also might bring water shortage risk due to the uncertain forecasts. This paper proposes a framework to determine the optimal operating rules for flood control considering pre-release based on uncertain forecasts. The framework includes three models: a pre-release model at the early stage of the flood to enlarge the flood control storage capacity; a multi-objective optimization model with resilience and risk as objectives at the flood regulating stage to optimize the flood control operating rules; a fuzzy optimum selecting model to determine the satisfied operating rule considering forecast uncertainty and decision-maker's preferences. In the framework, forecast uncertainty has been considered from the perspective of the forecast error distribution. Nierji Reservoir in Northeast China is taken as a case study. Results show that compared with the existing operating rule, the recommended operating rule considering pre-release releases water more evenly and can not only decrease the peak flow at the downstream protection point but also improve the downstream flood resilience without increasing reservoir risk. The proposed framework that considers forecast error distribution provides higher superiority degrees of the rules than the traditional framework that considers the maximum and minimum forecast errors in the real-time operation of the 1969 and 2013 flood hydrographs.

Investigation on the Injection Pattern of Intermittent Natural Gas Flooding in Ultra-Low Permeability Reservoirs

Natural gas is a viable oil displacement agent in ultra-low-permeability reservoirs due to its good fluidity. It can also cause gas channeling during continuous injection, which limits its oilfield application. In order to relieve gas channeling during natural gas flooding, the injection mode should be changed. The use of intermittent natural gas injection (IGI) after the continuous natural gas injection in an ultra-low-permeability reservoir is proposed, and optimization of the injection parameters is discussed. The results show that IGI can be divided into three stages, the gas injection stage, the well shutting stage and the oil production stage. With the increase in injection time, the oil recovery enhances obviously as a result of IGI because the gas fingering can be controlled at the well shutting stage, and the gas/liquid ratio grows slowly because the gas breakthrough can be reduced at the oil production stage. The oil recovery improves with the increase in cycle time of IGI, while the increase rate reduces evidently after the cycle time reaches 360 min. The oil recovery increment is low if the cycle index exceeds 3 in the ultra-low-permeability reservoir. Thus, the optimal cycle time for each round and the appropriate cycle index of IGI are 360 min and three rounds.

Implications of sand mobilization on stability and rheological properties of carbon dioxide foam and its transport mechanism in unconsolidated sandstone

This study reports the role of sand grain (of varying size: 60–380 μm and concentration: 0–3 wt%) on stability and properties of Pickering carbon dioxide (CO2) foam, which relates to foam transport problem during oil recovery practice in unconsolidated formation. For foams, anionic surfactant (sodium dodecyl sulfate: 0.2 wt%) and single-step silica nanofluid (0.1 wt%, size: 33–38 nm) were used and Pickering foams were prepared by mechanical agitation in the presence of different sand (comprised mainly of quartz with traces of clay), to mimic the effect of grain on foam stability. Interestingly, a varying stability exists in presence of sand. Thus, foam volume increased from 48 ml (without sand) to 58 ml when 1 wt% sand (of size ≈ 60–120 μm) was added while it further reduced to 46 and 40 ml with 2 and 3 wt% sand, respectively. On the contrary, foam stability continuously reduced with increment in sand size (from 60 to 120 to 200–380 μm), indicating unfavorable role of sand size on foam stability. Thus, sand production during oil recovery process is unfavorable for the stability of foam systems. The effect of sand concentration and size on foam properties was validated by interfacial tension and rheological measurements. Interfacial tension between CO2-nanofluid decreased till 1 wt% sand, suggesting favorable role of sand on CO2-nanofluid interaction. Similarly, CO2 foam showed maximum viscosity (72.8 mPa s) at 1 wt% sand (of size ≈ 60–120 μm) while further increase in concentration (>1 wt%) and size (>120 μm) reduced foam viscosity. These foams also exhibited viscoelastic characteristics with presence of both storage and viscous moduli. The solid-like nature of foam was least affected by the increase in deformational strain and foams exhibited dominating storage modulus over the range strain explored. Thus, the observation of this study can be used to optimize foam flooding in sandstone reservoirs which exhibit sand/fines production.

Real-time adjustment way of reservoir schedule forecasting projects based on improved variable oblivion factor least square arithmetic coupling Kalman filters

Flood forecasting method is an important non-engineering power generation scheduling method. However, due to various sources of uncertainty and the influence of observation and other factors, there are always errors in the results of flood forecasting, and these errors will reduce the application effect of the forecast results in reservoir optimization. Therefore, in order to improve the accuracy, we should analyze the sources of uncertainty, estimate the probability of the error range, and thus reduce the forecast error. In this paper, three improved real-time adjustment methods of variable forgetting factor least squares arithmetic coupled Kalman filter are proposed: adaptive Kalman method, ZK method and KZ method. It effectively avoids the shortcomings of the traditional Kalman method. We adjusted the Feng Shu Ba Reservoir flood forecast in real time for example, and then applied it and compared it with other methods. The results show that they have better simulation effect.

Physical and numerical simulation of inter-fracture flooding in heterogeneous tight oil reservoirs

The existing tight oil reservoirs are mainly developed after hydraulic fracturing of horizontal Wells with low recovery. Traditional enhanced oil recovery (EOR) methods are difficult to apply in tight reservoirs, because huff-puff drives oil to the distal end, water breakthrough exists in inter-well flooding, and ASP flooding cannot enter the small pore throat of the tight reservoir. A new EOR method of inter-fracture flooding is proposed. This method solves the problem that the injection water cannot enter the matrix in tight reservoir by inter-fracture flooding. Inter-fracture flooding reduces the distance between the injection and production ends and reduces the risk of water channeling. Inter-fracture flooding increases the pressure gradient during water flooding in the reservoir and establishes an effective water displacement system in the heterogeneous tight reservoir. In this paper, physical simulation experiments and numerical simulation are designed to study the EOR effect of inter-fracture water flooding in heterogeneous tight reservoirs. The results showed the following: (1) Inter-fracture asynchronous water flooding (IFAWF) can improve oil displacement efficiency by 6%–16% compared with inter-fracture synchronous water flooding (IFSWF). (2) Compared with IFSWF, IFAWF can greatly improve the oil displacement efficiency of the core with low permeability in the heterogeneous model by more than 20%. (3) Effective water sweep cannot be achieved by IFSWF, but can be achieved by IFAWF. (4) IFAWF established effective displacement in 0.1mD tight heterogeneous reservoir. Studies have shown that inter-fracture flooding can lower the reservoir development permeability threshold and will be an important EOR method for tight oil and shale oil in the future.