Influence of pore structure heterogeneity on channeling channels during hot water flooding in heavy oil reservoir based on CT scanning

Hot water flooding is an effective way to develop heavy oil reservoirs.However,local channeling channels may form,possibly leading to a low thermal utilization efficiency and high water cut in the reservoir.The pore structure heterogeneity is an important factor in forming these channels.This study proposes a method that mixes quartz sand with different particle sizes to prepare weakly heterogeneous and strongly heterogeneous models through which hot water flooding experiments are conducted.During the experiments,computer tomography(CT)scanning identifies the pore structure and micro remaining oil saturation distribution to analyze the influence of the pore structure heterogeneity on the channeling channels.The oil saturation reduction and average pore size are divided into three levels to quantitatively describe the relationship between the channeling channel distribution and pore structure heterogeneity.The zone where oil saturation reduction exceeds 20%is defined as a channeling channel.The scanning area is divided into 180 equally sized zones based on the CT scanning images,and threedimensional(3D)distributions of the channeling channels are developed.Four micro remaining oil distribution patterns are proposed,and the morphology characteristics of micro remaining oil inside and outside the channeling channels are analyzed.The results show that hot water flooding is more balanced in the weakly heterogeneous model,and the oil saturation decreases by more than 20%in most zones without narrow channeling channels forming.In the strongly heterogeneous model,hot water flooding is unbalanced,and three narrow channeling channels of different lengths form.In the weakly heterogeneous model,the oil saturation reduction is greater in zones with larger pores.The distribution range of the average pore size is larger in the strongly heterogeneous model.The network remaining oil inside the channeling channels is less than outside the channeling channels,and the hot water converts the network remaining oil into cluster,film,and droplet remaining oil.

Application of New Water Flooding Characteristic Curve in the High Water-Cut Stage of an Oilfield

The oil production predicted by means of the conventional water-drive characteristic curve is typically affected by large deviations with respect to the actual value when the so-called high water-cut stage is entered.In order to solve this problem,a new characteristic relationship between the relative permeability ratio and the average water saturation is proposed.By comparing the outcomes of different matching methods,it is verified that it can well reflect the variation characteristics of the relative permeability ratio curve.Combining the new formula with a reservoir engineering method,two new formulas are derived for the water flooding characteristic curve in the high water-cut stage.Their practicability is verified by using the production data of Mawangmiao and Xijiakou blocks.The results show that the error between the predicted cumulative oil production and production data of the two new water drive characteristic curves is less than the error between the B-type water drive characteristic curve and the other two water drive characteristic curves.It is concluded that the two new characteristic curves can be used to estimate more accurately the recoverable reserves,the final recovery and to estimate the effects of water flooding.

Effects of physical parameter range on dimensionless variable sensitivity in water flooding reservoirs

The similarity criterion for water flooding reservoir flows is concerned with in the present paper. When finding out all the dimensionless variables governing this kind of flow, their physical meanings are subsequently elucidated. Then, a numerical approach of sensitivity analysis is adopted to quantify their corresponding dominance degree among the similarity parameters. In this way, we may finally identify major scaling law in different parameter range and demonstrate the respective effects of viscosity, permeability and injection rate.

A production prediction method of single well in water flooding oilfield based on integrated temporal convolutional network model

Since the oil production of single well in water flooding reservoir varies greatly and is hard to predict, an oil production prediction method of single well based on temporal convolutional network(TCN) is proposed and verified. This method is started from data processing, the correspondence between water injectors and oil producers is determined according to the influence radius of the water injectors, the influence degree of a water injector on an oil producer in the month concerned is added as a model feature, and a Random Forest(RF) model is built to fill the dynamic data of water flooding. The single well history is divided into 4 stages according to its water cut, that is, low water cut, middle water cut, high water cut and extra-high water cut stages. In each stage, a TCN based prediction model is established, hyperparameters of the model are optimized by the Sparrow Search Algorithm(SSA). Finally, the models of the 4 stages are integrated into one whole-life model of the well for production prediction. The application of this method in Daqing Oilfield, NE China shows that:(1) Compared with conventional data processing methods, the data obtained by this processing method are more close to the actual production, and the data set obtained is more authentic and complete.(2) The TCN model has higher prediction accuracy than other 11 models such as Long Short Term Memory(LSTM).(3) Compared with the conventional full-life-cycle models, the model of integrated stages can significantly reduce the error of production prediction.

Displacement behavior and mechanism of long-term water flooding in sandstone oil reservoirs

Sandstone oil reservoirs with huge bottom water and high permeability are generally developed with high flow rate.After long-term water flooding(LTWF),the water flooding characteristics are quite different from that of original reservoir.In this paper,the effects of the PV number,viscosity,and displacement rate during LTWF are studied through experiments.The mechanism is analyzed based on analysis of changes in oil composition,rock mineral composition and wettability.The oil-water relative permeability curves,oil recovery and wettability were obtained with new experiments methods,which avoids the oil metering error by measuring oil and water separately.The research indicates that when the viscosity increases,the water phase permeability decreases,the residual oil saturation increases,and the water content rate increases earlier.A higher water flooding rate results in a higher ultimate recovery.A higher asphaltene content results in a higher viscosity and more oil-wet reservoir conditions.After LTWF,the wettability tends to water-wet,which is more favorable for heavy oil recovery.Moreover,LTWF reduces the clay content,which creates a more water-wet surface and a larger reservoir pore throat environment.This research provides insightful characteristics of offshore sandstone oil reservoirs,which can be used to enhance oil recovery.

Effects of salinity and ionic composition of smart water on mineral scaling in carbonate reservoirs during water flooding

This work was conducted to study the risk of formation damage as the result of mineral scales deposition during smart waterflooding into carbonate core sample,as well as the influence of injected water salinity and ionic composition on mineral scaling and precipitation.The reservoir flowing conditions were simulated by a new laboratory core-flooding procedure,which took into count of the effect of in-situ contact time(CT)of injected water and formation water on scaling.After the optimum CT was determined,extent of permeability decline was studied by the change in the salinity and ionic composition of injection seawater.The scaled core sample was analyzed visually by scanning electron microscopy(SEM)to study the crystal morphology of the scale.Under the experimental conditions,extent of permeability decline caused by CaSO_(4) and CaSO_(3) composite scales ranged from 61% to 79.1% of the initial permeability.The salinity and the ionic composition of injected smart water,and CT of the mixing waters had significant effects on the co-precipitation of CaSO_(4) and CaSO_(3) scales.The SEM images reveal that the loss of permeability is mainly caused by the accumulation and growth perpendicular to the pore wall of scale crystals.

Inter-well interferences and their influencing factors during water flooding in fractured-vuggy carbonate reservoirs

Based on the characteristics of injection-production units in fractured-vuggy carbonate reservoirs,nine groups of experiments were designed and performed to analyze the interference characteristics and their influencing factors during water flooding.Based on percolation theory,an inversion model for simulating waterflooding interferences was proposed to study the influence laws of different factors on interference characteristics.The results show that well spacing,permeability ratio,cave size,and cave location all affect the interference characteristics of water flooding.When the cave is located in high permeability fractures,or in the small well spacing direction,or close to the producer in an injection-production unit,the effects of water flooding are much better.When the large cave is located in the high-permeability or small well spacing direction,the well in the direction with lower permeability or smaller well spacing will see water breakthrough earlier.When the cave is in the higher permeability direction and the reserves between the water injector and producer differ greatly,the conductivity differences in different injection-production directions are favorable for water flooding.When the injection-production well pattern is constructed or recombined,it’s better to make the reserves of caves in different injection-production directions proportional to permeability,and inversely proportional to the well spacing.The well close to the cave should be a producer,and the well far from the cave should be an injector.Different ratios of cave reserves to fracture reserves correspond to different optimal well spacings and optimal permeability ratios.Moreover,both optimal well spacing and optimal permeability ratio increase as the ratio of cave reserves to fracture reserves increases.

Mechanisms of remaining oil formation by water flooding and enhanced oil recovery by reversing water injection in fractured-vuggy reservoirs

To get a deeper understanding on the formation mechanisms and distribution laws of remaining oil during water flooding, and enhanced oil recovery(EOR) mechanisms by reversing water injection after water flooding, 3D visualization models of fractured-vuggy reservoir were constructed based on the elements and configuration of fractures and vugs, and typical fracture-vug structures by using advanced CT scanning and 3D printing technologies. Then, water flooding and reversing water injection experiments were conducted. The formation mechanisms of remaining oil during water flooding include inadequate injection-production well control, gravity difference between oil and water, interference between different flow channels, isolation by low connectivity channel, weak hydrodynamic force at the far end. Under the above effects, 7 kinds of remaining oil may come about, imperfect well-control oil, blind side oil, attic oil at the reservoir top, by-pass residual oil under gravity, by-pass residual oil in secondary channel, isolated oil in low connectivity channel, and remaining oil at far and weakly connected end. Some remaining oil can be recovered by reversing water injection after water flooding, but its EOR is related to the remaining oil type, fracture-cavity structure and reversing injection-production structure. Five of the above seven kinds of remaining oil can be produced by six EOR mechanisms of reversing water injection: gravity displacement, opening new flow channel, rising the outflow point, hydrodynamic force enhancement, vertically equilibrium displacement, and synergistic effect of hydrodynamic force and gravity.

Hydrogeochemical Simulation of Water-Rock Interaction Under Water Flood Recovery in Renqiu Oilfield, Hebei Province, China

Hydrogeochemical simulation is an effective method to study water-rock interaction. In this paper, PHREEQM was used for the simulation of water-rock interaction under water flooding in the Renqiu Oilfield. Calculated results revealed that when fresh water was injected into the reservoir, Cl\+- and Na\++ would decrease without involvement in water-rock interaction. Erosion to dolomite will lead to an increase in Ca\+\{2+\}, Mg\+\{2+\} and CaHCO\++\-3. Saturation index of calcite and aragonite decreased first and then increased. With fresh water accounting for up to 70%, mixed water has the strongest erosion ability. Deoiled water has erosion ability under high temperature and high partial pressure of CO\-2. Pyrite and gypsum were sensitive to deoiled water, which can cause the dissolution of pyrite and the precipitation of gypsum. Micrographs revealed a great deal of information about water-rock interaction.

Three-Dimensional Imaging of Pore-Scale Water Flooding Phenomena in Water-Wet and Oil-Wet Porous Media

The penetration of water during water flooding has been observed over many years using several methods. A microfocused X-ray computed tomography scanner can be used to directly observe 3D water flooding in a nondestructive manner. To eliminate the possibility of false images being produced because of X-ray broadening effects, we developed a visualization method by arranging the brightness distribution of all phases involved. Water flooding experiments were conducted using oil-wet and water-wet porous media. The water phase was injected upward into packed glass beads containing an oil phase, and the process was scanned every minute until steady state was reached. Using this scheme, real-time, the water invasion pattern and oil trapping process in clusters of pores and individual pores can be observed clearly. By eliminating false images, the boundary of each phase could be identified with high precision, even in a single pore. Porelevel phenomena, including snap off (which has never before been captured in a real 3D porous medium), piston-like displacement, and the curvature of the interface, were also observed. Direct measurement of the pore throat radius and the contact angle between the wetting and nonwetting phases gave an approximation of the capillary pressure during the piston-like displacement and snap-off processes.

3D Physical Simulation of Water Flooding Characteristics of Buried Hill Reservoir with Different Fracture Systems

In order to understand the water-flooding characteristics of different fracture systems in metamorphic rock buried hill reservoirs and the mechanism of improving water-flooding development effect, a three-dimensional physical model of fractured reservoirs is established according to the similarity criterion based on the prototype of metamorphic buried hill reservoirs in JZ Oilfield in Bohai Bay Basin. Combined with the fractured reservoir characteristics of JZ Oilfield, the water displacement characteristics of the top-bottom staggered injection-production well pattern in different fracture network mode and different fracture development degree of buried hill reservoir are studied. The experimental results show that: 1) the more serious the fracture system irregularity is, the shorter the water-free oil production period is and the lower the water-free oil recovery is. After water breakthrough of production wells, the water cut rises faster, and the effect of water flooding development is worse;2) under the condition of non-uniform fracture development, the development effect of the bottom fracture undeveloped is better than that of the middle fracture undeveloped. Water injection wells are deployed in areas with relatively few fractures, while oil wells are deployed in fractured areas with higher oil recovery and better development effect.

Research and Application of Water Flooding Timing and Method for Blocky Bottom Water Fractured Buried Hill Reservoir

Oilfield A is a fractured buried hill reservoir in Bohai bay of China. In order to solve the difficult problem of water flooding timing and method in oilfield. Considering the characteristics of the buried hill fractures with stress sensitivity and strong heterogeneity, the ECLIPSE software was used in the research, and a three-dimensional injection-production numerical model for horizontal wells in buried hill reservoirs is established. According to the main research factors in water flooding, a series of water flooding schemes are designed, and the optimization of water flooding timing, oil recovery rate and water flooding mode in buried hill reservoirs were carried out. The results show that the optimum pressure level of fractured reservoir is about 70% of the original reservoir pressure. The optimal water flooding method is the conventional water flooding in the initial stage, when the water cut reaches 80%, it is converted into periodic water flooding. The oil recovery is the highest when the water injection period is 4 months. Field tests show that conventional water flooding is carried out in the initial stage of the oilfield A when the pressure is reduced to 70% of the original. Periodic water flooding is carried out when water cut is 80%. Good development results had been achieved in the 10 years since oilfield A was put into production. The average productivity of single well reached 300 m3/d in the initial stage, at present, the water cut is 60%, and the recovery degree is 18.5%, which is better than that of similar oilfields. This technology improves the water flooding effect of blocky bottom water fractured dual media reservoirs in metamorphic buried hills, and provides a reference for the development of similar reservoirs.

Water flooding flowing area identification for oil reservoirs based on the method of streamline clustering artificial intelligence

For the case of carbonate reservoir water flooding development, the flow field identification method based on streamline modeling result was proposed. The Ocean for Petrel platform was used to build the plug-in that exported the streamline data, and the subsequent data was processed and clustered through Python programming, to display the flow field with different water flooding efficiencies at different time in the reservoir. We used density peak clustering as primary streamline cluster algorithm, and Silhouette algorithm as the cluster validation algorithm to select reasonable cluster number, and the results of different clustering algorithms were compared. The results showed that the density peak clustering algorithm could provide better identified capacity and higher Silhouette coefficient than K-means, hierachical clustering and spectral clustering algorithms when clustering coefficients are the same. Based on the results of streamline clustering method, the reservoir engineers can easily identify the flow area with quantification treatment, the inefficient water injection channels and area with developing potential in reservoirs can be identified. Meanwhile, streamlines between the same injector and producer can be subdivided to describe driving capacity distribution in water phase, providing useful information for the decision making of water flooding optimization, well pattern adjustment and deep profile modification.

Experiments on the influences of well pattern on water flooding characteristics of dissolution vug-cave reservoir

Based on the similarity criterion, volcanic rock samples were taken from outcrops to make experimental models. Water flooding experiments of five-spot well pattern, nine-spot well pattern, five-spot to nine-spot well pattern, the relationship between relative well and fracture positions, and injection rate in dissolution vug-cave reservoirs with/without fractures were carried out to analyze variation regularities of development indexes, find out development characteristics of water flooding with different well patterns and sort out the optimal water flooding development mode. For dissolution vug-cave reservoirs without fractures, five-spot well pattern waterflooding has very small sweeping area, serious water channeling and low oil recovery. When the well pattern was adjusted from five-spot to nine-spot well pattern, oil recovery could be largely improved, but the corner well far from the injector is little affected. In dissolution vug-cave reservoirs with fractures, when the injector and producer are not connected by fractures, the fractures could effectively connect the poorly linked vugs to improve the development effect of water flooding. Whether there are fractures or not in dissolution vug-cave reservoirs, the development effect of nine-spot well-pattern is much better than that of five-spot well pattern and five-spot to nine-spot well pattern, this is more evident when there are fractures, and the edge well has better development indexes than corner well. At the high-water cut stage of water flooding with nine-spot well pattern, the oil recovery can be further improved with staggered line-drive pattern by converting the corner well into injection well. It is helpful to increase the oil production of corner well of nine-spot well pattern by increasing the injection rate, and improve ultimate oil recovery, but the water-free production period would be greatly shortened and water-free recovery would decrease.

Two-phase flow thermo-hydro-mechanical modeling for a water flooding field case

Simulation of subsurface energy system involves multi-physical processes such as thermal,hydraulical,and mechanical(THM)processes,and requires a so-called THM coupled modeling approach.THM coupled modeling is commonly performed in geothermal energy production.However,for hydrocarbon extraction,we need to consider multiphase flow additionally.In this paper,we describe a three-dimensional numerical model of non-isothermal two-phase flow in the deformable porous medium by integrating governing equations of two-phase mixture in the porous media flow in the reservoir.To account for inter-woven impacts in subsurface condi-tions,we introduced a temperature-dependent fluid viscosity and a fluid density along with a strain-dependent reservoir permeability.Subsequently,we performed numerical experiments of a ten-year water flooding pro-cess employing the open-source parallelized code,OpenGeoSys.We considered different well patterns with colder water injection in realistic scenarios.Our results demonstrate that our model can simulate complex interactions of temperature,pore pressure,subsurface stress and water saturation simultaneously to evaluate the recovery per-formance.High temperature can promote fluid flow while cold water injection under non-isothermal conditions causes the normal stress reduction by significant thermal stress.Under different well patterns the displacement efficiency will be changed by the relative location between injection and production wells.This finding has provided the important reference for fluid flow and induced stress evolution during hydrocarbon exploitation under the environment of large reservoir depth and high temperature.

Water flooding optimization with adjoint model under control constraints

The oil recovery enhancement is a major technical issue in the development of oil and gas fields. The smart oil field is an effective way to deal with the issue. It can achieve the maximum profits in the oil production at a minimum cost, and represents the future direction of oil fields. This paper discusses the core of the smart field theory, mainly the real-time optimization method of the injection-production rate of water-oil wells in a complex oil-gas filtration system. Computing speed is considered as the primary prerequisite because this research depends very much on reservoir numerical simulations and each simulation may take several hours or even days. An adjoint gradient method of the maximum theory is chosen for the solution of the optimal control variables. Conven-tional solving method of the maximum principle requires two solutions of time series： the forward reservoir simulation and the backward adjoint gradient calculation. In this paper, the two processes are combined together and a fully implicit reservoir simulator is developed. The matrixes of the adjoint equation are directly obtained from the fully implicit reservoir simulation, which accelera-tes the optimization solution and enhances the efficiency of the solving model. Meanwhile, a gradient projection algorithm combined with the maximum theory is used to constrain the parameters in the oil field development, which make it possible for the method to be applied to the water flooding optimization in a real oil field. The above theory is tested in several reservoir cases and it is shown that a better development effect of the oil field can be achieved.

Theoretical exploration of water injection gravity flooding oil in ultra-deep fault-controlled fractured-cavity carbonate reservoirs

Based on the analysis of geological characteristics of ultra-deep fault-controlled fracture-cavity carbonate reservoirs and division of reservoir units, two physical models were made, and physical simulations of oil displacement by water injection were carried out to find out water flooding mechanism in the fault-controlled fracture-cavity carbonate reservoir under complex flow state. On this basis, a mathematical model of fault-controlled carbonate reservoir with coexisting seepage and free flow has been established. Pilot water injection tests have been carried out to evaluate the effects of enhancing oil recovery by water injection. The results show that: fault-controlled fracture-cavity carbonate reservoir units can be divided into three types:the strong natural energy connected type, the weak natural energy connected type and the weak natural energy isolated type;the fault-fracture activity index of the fault-controlled fractured-cavity body can effectively characterize the connectivity of the reservoir and predict the effective direction of water injection;the mathematical model of fault-controlled carbonate reservoir with coexisting seepage and free flows can quantitatively describe the fluid flow law in the fracture-cavity body;the water injected into the fault-controlled fracture-cavity body is weakly affected by the capillary force of the lithologic body, and the oil-water movement is mainly dominated by gravity. The development modes of single well water injection, unit water injection,and single well high pressure water injection proposed based on the connection structure of fracture-cavity space and well storage space configuration are confirmed effective by pilot tests, with obvious water injection gravity flooding effect.

A 3-D SPH model for simulating water flooding of a damaged floating structure

With the quasi-static analysis method, the terminal floating state of a damaged ship is usually evaluated for the risk assessment. But this is not enough since the ship has the possibility to lose its stability during the transient flooding process. Therefore, an enhanced smoothed particle hydrodynamics（SPH） model is applied in this paper to investigate the response of a simplified cabin model under the condition of the transient water flooding. The enhanced SPH model is presented firstly including the governing equations, the diffusive terms, the boundary implementations and then an algorithm regarding the coupling motions of six degrees of freedom（6-DOF） between the structure and the fluid is described. In the numerical results, a non-damaged cabin floating under the rest condition is simulated. It is shown that a stable floating state can be reached and maintained by using the present SPH scheme. After that, three-dimensional（3-D） test cases of the damaged cabin with a hole at different locations are simulated. A series of model tests are also carried out for the validation. Fairly good agreements are achieved between the numerical results and the experimental data. Relevant conclusions are drawn with respect to the mechanism of the responses of the damaged cabin model under water flooding conditions.

Water flooding behavior in flow cells for ammonia production via electrocatalytic nitrogen reduction

The green production of ammonia,in an electrochemical flow cell under ambient conditions,is a promising way to replace the energy-intensive Haber-Bosch process.In the operation of this flow cell with an alkaline electrolyte,water is produced at the anode but also required as an essential reactant at the cathode for nitrogen reduction.Hence,water from the anode is expected to diffuse through the membrane to the cathode to compensate for the water needed for nitrogen reduction.Excessive water permeation,however,tends to increase the possibility of water flooding,which would not only create a large barrier for nitrogen delivery and availability,but also lead to severe hydrogen evolution as side reaction,and thus significantly lower the ammonia production rate and Faradaic efficiency.In this work,the water flooding phenomenon in flow cells for ammonia production via electrocatalytic nitrogen reduction is verified via the visualization approach and the electrochemical cell performance.In addition,the effects of the nitrogen flow rate,applied current density,and membrane thickness on the water crossover flux and ammonia production rate are comprehensively studied.The underlying mechanism of water transport through the membrane,including diffusion and electro-osmotic drag,is precisely examined and specified to provide more insight on water flooding behavior in the flow cell.

The effect of physical property change on the water flooding development in Changqing oilfield Jurassic low permeability reservoir

Changqing old oilfield Jurassic reservoir's average calibration recovery is 24.7%,with geological reserves recovery of 16.6%,water cut of 65.2%.And most of Jurassic reservoirs are in the middle and later field life,part of them has entered the high water cut and high recovery stage.Traditional water flooding way for improving oil recovery becomes more difficult,and new method has to be considered.Maling oilfield BS district is a typical representative,with high water cut of 90.8%,high recovery percent of 26.1%and low oil recovery rate of 0.25%.To explore the new way to improve oil recovery,the polymer and surfactant(SP for short)important pilot test has been developed.The low permeability reservoir indoor core data in high water cut stage and inspection well results indicate that the reservoir permeability,pore combination characteristics and pore type changed greatly after long-term water flooding development.These changes bring more difficulties to the continue development,especially the high injection pressure,which can cause other problems for well pattern infilling and EOR.This paper takes the high injection pressure problem of Maling BS district Jurassic reservoir for example,analyzes the physical property change law on the following aspects:the development mode in the past,core analysis,formation sensitivity,interstitial matter,well test interpretation results,in order to help to further effective development and provide important parameters for tertiary oil recovery technique for similar reservoirs and others.