Ultra-high Water Cut Stage Research Articles

Practice and Understanding of Water Control and Tapping Potential of Small Well Spacing in Extra-high Water-cut Period

In 2010, a certain Gaotai block of Daqing Oilfield adopted a 106-metre-5-point area well pattern to implement the infilling adjustment. After years of development, the water-cut has increased from 91.29% at the initial production to 96.02%, with an average annual increase rate of 1.3%. However, due to small well spacing, high speed of injection and production, and low qualified rate of water injection, the decline rate of the block has reached more than 10%, which poses a challenge to stable production. On the basis of in-depth study of the principal contradiction issues, the development effect was significantly improved after comprehensive adjustment in accordance with the working ideas of precise geological research to clarify the direction of potential excavation, precise scheme design to find the location of potential excavation, precise technological measures to improve the effect of measures, and precise management means to improve the overall efficiency. In addition, the precise understanding of the remaining oil in the ultra-high water-cut stage, the precise policy technique and the practical experience gained in the development and adjustment are of guiding and reference significance to the control of the production decline and the rise of water-cut in the ultra-high water-cut stage.

Experimental investigation of immiscible water-alternating-gas injection in ultra-high water-cut stage reservoir

Water-alternating-gas (WAG) injection is recommended as a means of improving gas mobility control. This paper describes a series of coreflood tests conducted to investigate the potential for continuous gas injection and WAG injection in ultra-high water-cut saline reservoirs. The mechanisms of immiscible water-alternating-nitrogen injection on residual oil distribution are analyzed, and pore-scale analysis is conducted. The effect of injection parameters on residual oil distribution and recovery efficiency is also evaluated. Coreflood results show that tertiary oil recovery efficiency is significantly higher using WAG injection than continuous gas injection during the ultra-high water-cut period. Pore-scale visualization illustrates the movement of gas through the waterflooded channels into the pore space previously occupied by water and residual oil, which then becomes trapped. Injected gas breaks the force balance of microscopic residual oil and reduces residual oil saturation. This mobilizes the displaced/collected residual oil into large waterfilled pores and blocks several water channels. WAG flooding can decrease free-gas saturation and increase trapped-gas saturation significantly, resulting in decreased relative permeabilities of gas and water. The experimental results indicate that appropriate WAG design parameters could enhance recovery by 15.62% when the injected pore volume of water and gas in the cycle is 0.3 PV at a gas/water injection ratio of 2:1. The results from this study will allow researchers and reservoir engineers to understand and implement immiscible WAG injection as an enhanced oil recovery method in ultra-high water-cut stage reservoirs. Cited as: Kong, D., Gao, Y., Sarma, H., Li, Y., Guo, H., Zhu, W. Experimental investigation of immiscible water-alternating-gas injection in ultra-high water-cut stage reservoir. Advances in Geo-Energy Research, 2021, 5(2): 139-152, doi: 10.46690/ager.2021.02.04

Production prediction at ultra-high water cut stage via Recurrent Neural Network

Abstract A deep learning method for predicting oil field production at ultra-high water cut stage from the existing oil field production data was presented, and the experimental verification and application effect analysis were carried out. Since the traditional Fully Connected Neural Network (FCNN) is incapable of preserving the correlation of time series data, the Long Short-Term Memory (LSTM) network, which is a kind of Recurrent Neural Network (RNN), was utilized to establish a model for oil field production prediction. By this model, oil field production can be predicted from the relationship between oil production index and its influencing factors and the trend and correlation of oil production over time. Production data of a medium and high permeability sandstone oilfield in China developed by water flooding was used to predict its production at ultra-high water cut stage, and the results were compared with the results from the traditional FCNN and water drive characteristic curves. The LSTM based on deep learning has higher precision, and gives more accurate production prediction for complex time series in oil field production. The LSTM model was used to predict the monthly oil production of another two oil fields. The prediction results are good, which verifies the versatility of the method.

Study on start-up of residual oil for different grades of water flooding zones at ultra-high water-cut stage

At present stage, most of the oil reservoirs in China have entered the ultra-high water-cut period, and the heterogeneity is serious. The water flooding effects in different zones of the reservoirs are obviously different. The overall reservoir recovery degree is low, and there is still a large amount of remaining oil remaining in all grades of water flooding zones. This paper mainly carried out the relevant physical model experiment of the remaining oil in the ultra-high water-cut period, and simulated the recovery of the remaining oil under different subsequent flooding conditions after entering the ultra-high water-bath period of different grades of water flooding zones. The start-up law of the remaining oil in the different grades of water flooding zones was observed and analyzed. According to the experimental results, it can be seen that in the period of ultra-high water cut, the strong water flooded zone has a greater exploitation potential than the extreme water washing zone and the weak water flushed zone. Therefore, the focus of developing in the ultra-high water-cut stage should be placed on the strong water flooded zone, and the water flooding after adjusting the profile by injecting jelly can effectively improve the recovery rate of the strong water flooded zone.

Analysis of the index change laws of the B and C strips of Block A after well pattern infilling

After entering the ultra-high water cut stage, it is more and more difficult to tap the remaining oil potential, especially in the B and C strips because of the prominent contradictions between injection and production. It is difficult to adjust a injection well and get a good effect of well stimulation, so oil recovery is low. The index change laws are analyzed and summarized in two test areas of well pattern infilling, which can be used as a reference for the well pattern infilling and efficient development in the B and C strips.

Study on determination method of economic limit water cut of water drive oilfield in ultra-high water cut stage

According to the waterflooding characteristics in extra-high water cut stage of oilfield, a calculation model which is based on profit and loss balance principle has been created. This model can be used to identify the economic limit water cut of producers with different cost component. With the use of this model, the economic limit water cut in a development block of Daqing Oilfield with different oil prices has been calculated, and according to the economic benefit, producers have been classified into different group. This model is a significant basis of well shut-in and oil-field development.

New Waterflooding Characteristic Curves Based on Cumulative Water Injection

When a conventional waterflooding characteristic curve (WFCC) is used to predict cumulative oil production at a certain stage, the curve depends on the predicted water cut at the predicted cutoff point, but forecasting the water cut is very difficult. For the reservoirs whose pressure is maintained by water injection, based on the water-oil phase seepage theory and the principle of material balance, the equations relating the cumulative oil production and cumulative water injection at the moderately high water cut stage and the ultrahigh water cut stage are derived and termed the Yuan-A and Yuan-B curves, respectively. And then, we theoretically analyze the causes of the prediction errors of cumulative oil production by the Yuan-A curve and give suggestions. In addition, at the ultrahigh water cut stage, the Yuan-B water cut prediction formula is established, which can predict the water cut according to the cumulative water injection and solve the difficult problem of water cut prediction. The application results show Yuan-A and Yuan-B curves are applied to forecast oil production based on cumulative water injection data obtained by the balance of injection and production, avoiding reliance on the water cut forecast and solving the problems of predicting the cumulative oil production of producers or reservoirs that have not yet shown the decline rule. Furthermore, the formulas are simple and convenient, providing certain guiding significance for the prediction of cumulative oil production and water cut for the same reservoir types.

Formation mechanism and distribution characteristics of micro residual oil in ultra-high water cut reservoirs a case study of yangsanmu oilfield

The formation mechanism and distribution characteristics of microscopic remaining oil are the basis for efficient development and enhanced oil recovery of heavy oil reservoirs in ultra-high water cut stage. This paper takes Yangsanmu heavy oil reservoir in Huanghua depression as an example, micro-displacement simulation experiment based on microscopic pore structure analysis. Through parallel experiments, the remaining oil displacement effects of water flooding combined with polymer flooding, water flooding and surfactant polymer system combination, water flooding and poly-alkaline ternary composite flooding were compared. The formation mechanism and distribution pattern of remaining oil under different displacement medium conditions were studied to find a reasonable displacement medium system. The experimental results show that the formation of microscopic remaining oil in the study area is related to the stripping effect, the flow around, the pinch action occurs, the run through effect and the adherent flow. The distribution types of remaining oil are mainly angular type, pore wall oil film type, throat retention type, dispersed oil drop type and porphyritic remaining oil in macropores. The analysis of residual oil saturation under different displacement media shows that the combined flooding effect of water flooding and poly-alkaline ternary composite flooding are the best, followed by water flooding and surfactant polymer system combination flooding. This study provides guidance for the remaining oil exploration plan of the ultra-high water cut stage heavy oil reservoir in this area.

The research on the classification method of high water-cut well group in Y block

Y block has entered the ultra-high water cut stage of production, and the water cut of oil wells is generally higher than 90%. Before polymer flooding, water cut continues to rise. High-water-bearing wells in the injected area are characterized by difficulty in effectiveness and low water cut decline, which seriously affects the overall development effect of the area. In this paper, the high water-bearing wells are divided into four categories by the parameter index of the number of layers in the high water-bearing channels before polymer flooding.Through the splitstream curve and the phase permeability curve, the permeability and oil saturation data under the condition of 98% water content were selected for fitting, and the critical oil saturation formula was obtained.The ratio between the oil saturation and the critical oil saturation is calculated by numerical simulation, and the discriminant standard of the dominant seepage channel with high water content is established.Compared with previous remaining oil saturation field identification methods, changed the method according to the conventional ideas of remaining oil saturation evaluation of water and residual oil, through the analysis of reservoir permeability parameters for the current development under the condition of the target reservoir quantitative identification of the cause of high water cut, to cause high containing water wells and reservoir high water cut oilfield management work provide quantitative analysis and objective guidance.

Auto-optimization of production-injection rate for reservoirs with strong natural aquifer at ultra-high water cut stage

Abstract Based on the optimal control theory and taking the production law of reservoirs with strong natural aquifer as the basic constraint, a mathematical model of liquid production for such reservoirs in the later stage of development is established. The model is solved by improved simultaneous perturbation stochastic approximation algorithm (SPSA), and an automatic optimization software for liquid production is developed. This model avoids the disadvantage of traditional optimization methods that only focus on the maximum value of mathematics but ignore the production law of oilfield. It has the advantages of high efficiency of calculation, short period and automatic optimization. It can satisfy the automatic optimization of liquid production in later stage of oilfield development. The software was applied in the oilfield development of D oilfield, Ecuador in South America, and realized the automatic optimization of liquid production in the later stage of oilfield development.

Reservoir Classification and Evaluation Method Based on Storage-permeate and Degree of Heterogeneity

La-Sa-Xing oilfield is the maximum continental multi-layered sandstone reservoir in China, which has already entered the ultra-high water-cut development stage. Three major contradictions are more prominent and residual oil is highly scattered, the traditional qualitative reservoir evaluation method is hard to meet the demand of current reservoir production and development. According to the requirement of production situation and technology development at ultra-high water-cut stage, combining fine reservoir geological characteristics and development efficiency, a new reservoir evaluation method is established by using multi-parameter product method, multi-parameter bound analysis, etc. The method proposed is set up with storage-permeate assessment parameter and dominant sand-body distribution degree as assessment parameters. It establishes the relationship between static geology and dynamic production and reveals a certain oil-layer potential. The introduction of dominant sand-body distribution degree emphasizes the reservoir plane heterogeneous characters, it can quantitatively characterize the matching relationship between reservoir and well pattern; the reservoir classification based on the above two aspects providing reliable basis for designing water flood, polymer flood and ASP flood development plan.

Study on Development Law and Yield Replacement Method in Sazhong Development Area

with the increasing time of water drive development in the Sazhong development zone, the oilfield has gradually entered the stage of high water cut stage or ultra-high water cut stage, and now it has entered the development stage of the high water cut period of the coexistence of the two drive. In order to extend the production life of the oilfield and plan the scale of production, based on the application of reservoir engineering method to calculate the natural decline rate and by grouping the Sa Pu oil layer and the Gaotaizi oil reservoir in the Sazhong oilfield, reducing the yield base of each year and re prediction of water drive production decline rule in Sazhong development area, which is concluded that the average decline rate is 7.46%. At the same time, the characteristics of tertiary oil recovery are analyzed, and the production replacement equation is established through the production demand under different production decline conditions. Based on the law of decreasing water drive and the change rule of chemical flooding production, the average chemical drive reserves in 12th Five-Year and the annual largest chemical drive reserves as tertiary oil recovery reserves, and the output forecast index of the sash development zone can be obtained.

The Residual Potential of Bottom Water Reservoir Based upon Genetic Algorithm for the Relative Permeability Inversion

At present in the offshore oilfield, X oilfield had successfully developed bottom water reservoir with horizontal well. The development mode of single sand body of horizontal well caused water cut rose rapidly and irresistible bottom water coning. The common empirical formula of recoverable reserves obtained through statistical analysis was not applicable to the bottom water reservoir. Under the condition of as high as tens of thousands of time local scour multiple, underground seepage law had been changed. In order to improve the understanding of the remaining potential of bottom water reservoir in the ultra-high water cut stage, this research innovation proposed to carry out the flow tube simulation of the bottom water ridge. In addition, combining with the theoretical research of the quantitative characterization of the water ridge form and the vector permeability, theoretical model was established. At last, the phase permeability curve was calculated from the production data of the ultra-high water cut stage of the bottom water reservoir by combining the genetic algorithm. According to the change of water ridge and oil saturation, the mechanism of end point change of phase permeability curve was expounded, and the effective production radius of water drive oil in bottom water reservoir was put forward, which provided the basis for understanding the potential of oil field and tapping the potential in the future.

The study of horizontal well excavation technology of point bar during ultra-high water-cut stage based on flow field intensity evaluation

The Ming Huazhen group of Gang Dong Oilfield is a medium–high permeability reservoir of meandering stream deposits. It has a high areal and vertical heterogeneity and has entered the stage of extra-high water-cut. Point bar is an important development area for oil sands in meandering stream deposits and the development of a lateral layer is an important factor controlling the distribution of residual oil. The change rule of water displacement in medium–high permeability reservoirs was clearly determined by laboratory experiments. A numerical simulation method was used to determine the time-varying physical properties of the reservoir. Based on the internal configuration of the meandering river point bar, the horizontal well excavation method for residual oil development of point bars during the ultra-high water-cut stage is employed on the basis of the evaluation of flow field intensity. The results show that this method can well reflect the distribution of the flow field in a point bar sand body. The degree of extraction increases by 3.2% if horizontal wells are drilled in the weak flow field rather than in other places.

Study on Optimization of Combined Parameters of Subdivision Water Injection Layer Sections in Ultra-high Water Cut Stage

After 50 years of exploitation, Block A has entered the development stage of the ultra-high water cut stage. Although the layer series of development has been subdivided and adjusted, the interlayer interference is still serious, imposing difficulties in development adjustment. Based on dynamic production data and monitoring data analysis, this paper applies multi-disciplinary reservoir description technology and introduces economic evaluation indicators to quantitatively analyze the variation coefficient of permeability within subdivided layer sections, the number of monolayer breakthrough series and sections, the number of small layers within a layer section, and the effect of sandstone thickness on the subdivision and adjustment effect, analyze the influence of well test period and operation costs on the economic benefits, and the optimize combined parameters of subdivision water injection layer sections. After field application, the utilization proportion of sandstone in the soil layer with the subdivided well permeability of less than 0.1 μ m2 increased by 18.3 percentage points, and the average daily oil output per well in the surrounding wells increased by 0.3 t, effectively reducing the decline in output and increase in the water cut, and providing technical support for water flood fine potential tapping in the ultra-high water cut stage.

Microscopic Flow Characteristics of Fluids in Porous Medium and Its Relationship with Remaining Oil Distribution: A Case Study in Saertu Oilfield of Daqing in China

The Saertu Oilfield of Daqing in northeast China has entered ultrahigh water-cut stage of development. Numerical simulation is applied in this paper to study characteristics of microscopic fluid velocity and flow pressures variation in the core pores in the Beier Area of Saertu Oilfield. The relationship between the remaining oil distribution and microscopic flow characteristics of fluid in the pores has been analyzed. Study results show that, in the reservoir with stronger heterogeneity of grain size and throat (corresponding to high coordinate number), high flow velocities tend to occur in relatively wider pore throats with great differentiation of flow velocities. The dominant passages are developed in high capacity channel, the detour flows are created in large porous channels, and the isolated islands are formed in small porous channels. The flow velocity declines slowly with long duration of high pressure. Few pores are swept by injected fluids with low sweep efficiency. The microscopic remaining oil is mainly distributed in cluster state. The content of remaining oil is higher with lower oil displacement efficiency. By contrast, in the reservoir with weaker heterogeneity of grain size and throat (corresponding to low coordinate number), high flow velocities also develop in relatively narrower pore throats with little differentiation of flow velocities. The development of detour flows is weaker in large porous channels. The flow velocity declines quickly with a short duration of high pressure. More pores are swept by fluids with high sweep efficiency. The remaining oil is mainly distributed in state of thin film on pore surface. The content of remaining oil is lower with higher oil displacement efficiency.

New water drive characteristic curves at ultra-high water cut stage

Abstract A function expression of the oil-water relative permeability ratio with normalized water saturation at high water saturation was proposed based on statistics of measured oil-water relative permeability data in oilfields. This expression fits the later section of conventional relative permeability ratio curve more accurately. Two new water drive characteristic curves at the ultra-high water cut stage (fw>90%) were derived by combining the new oil-water relative permeability ratio expression and reservoir engineering method. Then, the numerical simulation results of five-point well pattern and production data of Yangerzhuang Oilfield and Liuzan Oilfield were used to verify the adaptability of the new water drive characteristic curves. The results showed that the new water drive characteristic curves are more accurate than conventional water drive characteristic curves after A type and B type water drive curves rise, and can be used to predict production performance at ultra-high water cut stage, ultimate recovery efficiency and recoverable reserves.

SISP to Enhance Oil Recovery at Ultra-high Water Cut Stage

This paper studied force condition of oil droplets in porous media and mechanism of separated-zone water injection and separated-zone oil production (SISP), considering the action of buoyancy on oil droplets during different stages of oilfield development. New idea SISP to enhance oil recovery is that different layers produce in different pressures by controlling fluid production and improving bottom pressure at ultra-high water cut stage. Three different vertical permeability model was designed and each with following five programs. The results show that the greater vertical permeability is, the bigger incremental recovery factor is. SISP is better than co-injection and co-production.

特高含水期剩余油受力状态方程及敏感分析

特高含水期剩余油受力状态方程及敏感分析

A new water drive curve at ultra-high water cut stage and application in prediction of oilfield development

For the water-flooded reservoir at ultra-high water cut stage, the ratio of oil and water relative permeability and the water saturation deviate from the linear relationship and show the downwarping trend in the semi-log coordinate, and the conventional water drive curves show the upwarping trend. Aiming at predicting the dynamic, recoverable reserve and recovery of oilfields at ultra-high water cut stage, a new formula characterizing the relation between the ratio of oil and water relative permeability and the water saturation was proposed, derivation of a new water drive curve was done by reservoir engineering methods, and the formula of recoverable reserve and recovery was derived. Comparison of the new water drive curve and the conventional one through numerical simulation and field application showed higher accuracy and better adaptability resulted from the new water drive curve, which solved the problems of upwarping and big prediction error in curves of ultra-high water cut stage.