Cyclic Waterflooding Research Articles

The Seepage Mechanism of Micro Remaining Oil During Cyclic Waterflooding in Low-permeability Reservoir

To explore the flow mechanism of micro-remaining oil during cyclic waterflooding in low-permeability reservoir, the displacement effect of micro-remaining oil under conventional waterflooding and different rounds of cyclic waterflooding was investigated by using a micro-visual displacement experiment based on microfluidics model. The produced ratio of different types of micro remaining oil during cyclic waterflooding was quantified, and major types of micro remaining oils that can be applied effectively during cyclic waterflooding were analyzed. Moreover, the flow mechanism of micro remaining oil during cyclic waterflooding was investigated. Research results demonstrated that clustering type remaining oil and columnar type remaining oil were major types that were applied during cyclic waterflooding. After three rounds of cyclic waterflooding, clustering-type remaining oil decreased by 2.50% on average, and columnar-type remaining oil decreased by 0.81% on average. The major mechanism of cyclic waterflooding is introduced as follows: at intervals of cyclic waterflooding, clustering type remaining oil and columnar type remaining oil exchange with water in pores, throats, and spaces between big and small pores due to the fluctuation of pressure field and effect of capillary force. As a result, oil and water redistribute. Clustering-type remaining oil and columnar-type remaining oil become movable oils.

Status and Prospect of Improved Oil Recovery Technology of High Water Cut Reservoirs

The high water cut stage is an important stage of the water injection development of oilfields because there are still more oil reserves available for recovery in this stage. Most oilfields have experienced decades of waterflooding development and adjustment. Although waterflooding reservoirs face the problems of the seriously watered-out and highly dispersed distribution of remaining oil, they remain dominant in waterflood development. This paper investigates the current situation of high-water content reservoirs and the methods available to improve oil recovery and elaborates on the fine reservoir description. Furthermore, it analyzes the main technical measures taken during the high water cut period, namely, secondary oil recovery waterflooding technology (including layer system subdivision, well pattern infilling, strengthening of water injection and liquid extraction, closure of high water cut wells, cyclic waterflooding technology, and water injection profile control) and tertiary oil recovery technology (represented by chemical flooding and gas flooding). In addition, this study reveals the mechanisms and effects of these methods on improving waterflooding development. Finally, this paper summarizes improved oil recovery technology and discusses the key directions and development prospects of this technology in enhancing the oil recovery rate.

Study of cyclic waterflooding for improving oil recovery in Lukeqin heavy oil reservoir

Long term water injection in Lukeqin heavy oil field results in a rapid increase of water cut. It is an urgent need to conduct a study on the influencing factors of heavy oil waterflooding. Experiments are used to conduct the effect of heavy oil viscosity change law on the development. Numerical simulation is used to analyze the viscosity and rhythmic conditions to clarify the production mechanism of waterflooding in heavy oil reservoirs. The feasibility study of cyclic water injection in heavy oil reservoirs is analyzed because water channeling is serious in continuous water injection, while cyclic waterflooding can slow down the injection water surge. To begin with, when using the improved cyclic waterflooding method, the working mode, reasonable number of cycles and the timing of cyclic waterflooding need to be optimized to obtain the optimal combination injection scheme. Furthermore, to investigate the mechanism of oil increase by cyclic waterfiooding, different production wells were divided into the channeling well, the seepage channel well and the normal wells according to the streamline strength, and then analyzed the mechanism influencing factor such as pressure difference and capillary force to study when cyclic waterflooding for the three types of production wells. Pressure differential are the most effective in increasing oil in the normal well, followed by the seepage channel well, and channeling well. The capillary force have the best water control effect on the channeling well, followed by the seepage channel well and the normal well. The capillary force play a dominant role in the well water control in the channeling well. The effect of increasing oil in the normal well is dominated by pressure difference. Well pressure difference and the capillary force have little to no dominant effect on the seepage channel well. The results demonstrate that cyclic waterflooding can effectively improve the recovery rate of three types of wells, with the degree of improvement from good to bad, in the order of the normal well, the channeling well and the seepage channel well. The novelty of this work lies in the combination of experimental and numerical models (mechanistic and practical) and simulation studies using three different types of wells, thus analyzing the mechanistic influence of pressure differential and capillary forces in it and concluding the dominant mechanism of action - the mechanism of development of heavy oil cyclic waterflooding is the effect of pressure difference control on production increase and capillary force control on reducing water cut.

Experimental evaluation of energy supplement methods in the Yanchang Oilfield shale reservoir

Shale oil development in the Yanchang Oilfield is characterized by rapid production decline and low productivity, and supplementing the energy requirements and enhancing the recovery of oil are major challenges for shale reservoir development. In this study, physical simulations of cyclic water flooding, CO2 immiscible huff and puff, CO2 miscible huff and puff, and gas–water alternate drive processes were conducted on Chang 7 shale reservoir samples from the Yanchang Oilfield. The mechanism behind micro-displacement was analyzed by online NMR detection technologies, which showed that the displacement should be kept above the minimum miscible pressure during CO2 huff and puff. Furthermore, our analyses showed the highest recovery rate was that of water–gas alternate flooding is due to its higher utilization of small pores. Overall, CO2–water alternating flooding or CO2 miscible huff and puff is recommended to obtain higher recovery rates, based on our results. Considering the economic benefits and construction conditions, cyclic water flooding can be used first and then converted to other modes. This study can provide theoretical support for different ways of supplementing energy and provides scientific guidance for gas injection pilot test in similar reservoirs.

Parameter Optimization of Asynchronous Cyclic Waterflooding for Horizontal-Vertical Well Patterns in Tight Oil Reservoirs.

Tight oil resources in China are mainly exploited by staged-fractured horizontal wells; horizontal wells face the problems of the rapid decline rate and low primary oil recovery. Pilot tests on the asynchronous cyclic waterflooding for the horizontal–vertical well pattern were carried out in recent years and achieved good performance. However, there are few studies on the influencing factors and parameter optimization of asynchronous cyclic waterflooding, which limits its wide application. This work took the tight oil reservoir in Yanchang formation, Fuxian area, Ordos Basin as its object, and the oil recovery mechanisms of asynchronous cyclic waterflooding for the horizontal–vertical well pattern were analyzed first. Then, the operation parameters of asynchronous cyclic waterflooding were optimized by the numerical simulation method. Among them, the injection proportion was optimized by the fuzzy synthetic evaluation method. Finally, the oilfield test was carried out based on the optimized parameters. The results showed that pressure disturbance and streamline deviation are the main oil recovery mechanisms of asynchronous cyclic waterflooding. The asynchronous mode of the diagonal well row is better than other asynchronous modes. For the injection time interval, injection–production ratio, and the injection and shut-in time, the cumulative oil production all show the trend of increasing first and then decreasing with the increase in these parameters. The optimal injection time interval and injection–production ratio are 0.5 T and 1, respectively. The optimal injection and shut-in time can be calculated by empirical formulas. Ultimately, the fuzzy synthetic evaluation model was established to optimize the injection proportion. Field practices showed that the average daily oil production of horizontal wells was increased from 1.7 to 3.0 m3 with the optimized parameters, which further verified the accuracy of the optimized parameters. This research can provide theoretical support for the effective development of tight oil reservoirs.

Study of Cyclic Waterflooding for Improving Oil Recovery in Lukeqin Heavy Oil Reservoir

Study of Cyclic Waterflooding for Improving Oil Recovery in Lukeqin Heavy Oil Reservoir

Research on reasonable development strategy of offshore buried hill fractured reservoir

In order to improve the overall production degree of offshore buried hill fractured reservoir, expand the swept volume of water flooding, and improve the reservoir development effect, according to the actual reservoir characteristic parameters, numerical simulation software and three-dimensional physical model are used to study the reasonable pressure level, injection production mode and water flooding strategy of Oilfield A. The results show that, according to the pressure sensitivity experiment and numerical simulation analysis, the reasonable formation pressure is 70% of the original pressure for the buried hill fractured reservoir, and higher recovery can be achieved at this pressure level. By comparing different injection and production mode schemes, it is determined that under the weak injection and forcible production mode, the swept volume of reservoir water flooding is the largest, the water free recovery period of production wells is longer, and the water cut rising rate is low. The reservoir development is divided into four stages. For different stages, depressurization production, pulse water flooding, cyclic water flooding and asynchronous water flooding strategies are adopted respectively. Compared with the conventional stable water flooding strategy, the balanced development of fractures and matrix can be realized, so as to improve the full cycle development effect of the reservoir. The application of the development strategy results in this study to oilfield production practice has played an obvious role in improving the development effect of fractured reservoir, which has field practical significance and can provide reference for the development of similar fractured reservoir.

Mechanism of Enhanced Oil Recovery for In-Depth Profile Control and Cyclic Waterflooding in Fractured Low-Permeability Reservoirs

When fractured low-permeability reservoirs enter a high water cut period, injected water always flows along fractures, water cut speeds increase rapidly, and oil production decreases quickly in oil wells. It is difficult to further improve the oil recovery of such fractured low-permeability reservoirs. In this paper, based on the advantages of in-depth profile control and cyclic water injection, the feasibility of combining deep profile control with cyclic water injection to improve oil recovery in fractured low-permeability reservoirs during the high water cut stage was studied, and the mechanisms of in-depth profile control and cyclic waterflooding were investigated. According to the characteristics of reservoirs in Zone X, as well as the fracture features and evolution mechanisms of the well network, an outcrop plate fractured core model that considers fracture direction was developed, and core displacement experiments were carried out by using the HPAM/Cr3+ gel in-depth profile control system. The enhanced oil recovery of waterflooding, cyclic water injection, and in-depth profile control, as well as a combination of in-depth profile control and cyclic water injection, was investigated. Moreover, variations in the water cut degree, reserve recovery percentage, injection pressure, fracture and matrix pressure, and water saturation were monitored. On this basis, the mechanism of enhanced oil recovery based on the combined utilization of in-depth profile control and cyclic waterflooding methods was analyzed. The results show that in-depth profile control and cyclic water injection can be synchronized to further increase oil recovery. The recovery ratio under the combination of in-depth profile control and cyclic water injection was 1.9% higher than that under the in-depth profile control and 5.6% higher than that under cyclic water injection. The combination of in-depth profile control and cyclic water injection can increase the reservoir pressure; therefore, the fluctuation of pressure between the matrix and its fractures increases, more crude oil flows into the fracture, and the oil production increases.

Experimental Study on Dynamic Characteristics of Shut-In and Restart Process in Water Drive Strong Heterogeneous Oil Reservoir

The main purpose of this investigation is to study the dynamic characteristics of shut-in and restart process in reservoirs with high water cut and strong vertical heterogeneity. The physical model, which includes three layers with low, medium, and high-permeability from top to bottom, was made according to the similarity law. Water drive test, the first restart test, and the second restart test were conducted, respectively. Water cut, oil recovery, and saturation distribution of the remaining oil were obtained during the tests. On this basis, mechanisms of shut-in and restart process of the reservoir were analyzed. It is concluded that appropriate developing plan such as layering mining and cyclic waterflooding should be implemented for developing strong heterogeneity reservoirs. The shut-in and restart tests showed that closing the water-flooded layer is beneficial for enlarging the sweep volume. Besides, water cut of 98% does not mean the economic limits of waterflooding. Under the effect of capillary force and gravitational differentiation, oil and water will redistribute in the formation. The redistribution of the oil and water, the fluctuation of the pressure difference, and the rebuild of the flow path, which produce parts of the bypassed oil, are the main mechanisms of the recovery enhancement by shut-in and restart operation. It should be noted that the shut-in and restart process indeed prolongs the waterflooding development. However, simply replying on the oil and water distribution under static conditions cannot greatly enhance the oil recovery.

Study on distribution characteristics of microscopic residual oil in low permeability reservoirs

In order to develop methods to further enhance oil recovery after water flooding in low permeability reservoirs by improving oil displacement efficiency, the displacement mechanism of residual oil was studied by the application of different pertinent measures. For in-depth investigation of oil displacement and variations in residual oil saturation, a large number of visual glass model displacement experiments were performed with different methods, such as changing the displacement direction, cyclic water flooding, displacement pressure difference variation and polymer flooding. In this paper, the models were divided into three (low, medium and high) permeability levels, and the residual oil after water flooding was categorized in five different types: cluster, oil film, oil drop, columnar and blind end residual oil. The experimental results showed that cluster residual oil accounted for the largest proportion after water flooding. In addition, with the increase in model permeability, cluster residual oil saturation increased and other types of residual oil saturations decreased. Compared to other methods, polymer flooding showed maximum displacement efficiency for the same displacement pressure and permeability model. The procedure was then followed by changing the displacement direction, cyclic water flooding and changing the displacement pressure difference. The different residual oil types can be activated by different methods, for example, cluster and columnar residual oil by changing the displacement direction, cluster and columnar residual oil by cyclic water flooding, cluster and oil drop residual oil by increasing displacement pressure difference. Moreover, all of the above mentioned five (05) types of residual oil can be activated by polymer flooding.

ASSESSING THE EFFECTIVENESS OF CYCLIC WATERFLOODING IN PK1-3 FORMATION OF THE VOSTOCHNO-MESSOYAKHSKOYE OIL FIELD

We have estimated the effectiveness of cyclic waterflooding in PK1-3 formation of the Vostochno-Messoyakhskoye oil field. This reservoir is saturated with high-viscosity oil. The obtained data are described in the article. The calculations have been performed on different simulations models with multiple variations of lateral and vertical heterogeneity of the reservoir. The result of our work is the program of cyclic waterflooding research for the VostochnoMessoyakhskoye oil field.

О выборе участков нефтяных месторождений для эффективного применения циклического заводнения

О выборе участков нефтяных месторождений для эффективного применения циклического заводнения

Feasibility study on cyclic water flooding of high saturation sandstone reservoir in late development stage - A case study of C30 fault block in Chaheji oilfield

There are some problems of high saturation sandstone reservoir in late development stage, such as low reservoir pressure level, low oil production volume and high water content ratio. At present, the conventional treatment measures are poor to improve the reservoir development efficiency. Through extensive investigation and comprehensive analysis, the cyclic water flooding method can effectively improve the reservoir development efficiency. This study is based on the theory of cyclic water flooding method to replace remaining oil. The numerical simulation of cyclic water flooding is carried out by establishing geological model of actual blocks. By analysing the influence of injection-production ratio, injection-production method and liquid production volume on the cyclic water flooding development efficiency, the cyclic water flooding scheme of high saturation sandstone reservoir in the late development stage is optimized.

Forecasting the parameters of non-stationary water flooding of oil deposits

Non-stationary flooding and water withdrawal with changing the direction of filtration flow as a secondary advanced recovery method allow enhancing oil deposit coverage by filtration processes, reducing or eliminating the amount of bypassed oil in productive formations. Process modelling should be provided for correct forecast about the efficiency of non-stationary formation stimulation. A formation model was designed for modelling cyclic water flooding. There are cross-flows between interlayers of reservoir robbing which have different porosity and permeability properties and unbalanced thrust in pore space. It is noted that when applying ordinary water flooding, high formation heterogeneity, higher than average oil viscosity and low permeability make it impossible to reach even average efficiency of oil pool development. The choice of a stimulation technique and its justification is an important step of planning in order to apply non-stationary stimulation. A possibility to apply non-stationary flooding efficiently for the analysed object has been established.

Water Injection Study in a Block Cycle

Block reservoir sand body main front deposition within the channel sand is given priority to, less layers, the thickness of thin sand body development, small scale, more is given priority to with narrow channel sand, water cut rising too fast in the process of oilfield development, plane, small interlayer adjustment scope, difficult to control the production decline and water cut rising speed, oil use degree is high, poor development effect. Under the condition of steady water injection, it is very difficult to expand the affected volume, and most of the water in the water channel is produced by the water channelling to the ground, making the injected water use less and less. It can improve the effect of oilfield development by adopting periodic water injection and preliminary exploration of stable yield path. Cyclic water flooding is the use of the existing well pattern, through the adjustment of the pressure field, the remaining oil used up state, improve the utilization rate of injected water and controlling water cut rising speed, delay of water breakthrough time, enlarge the swept volume of injected water, improve water drive recovery factor. It is an effective way to explore the effect of water flooding in high water content period.

Process Design of Cyclic Water Flooding by Real-Time Monitoring

The gradual decline in the oil production rate of water flooded reservoirs leads to decrease in the profit of water flooding system. Although cyclic water injection (CWI) was introduced to reduce the descending trend of oil production in water flooded reservoirs, it must be optimized based upon the process parameters. The objective of this study is to develop all process design criteria based upon the real-time monitoring of CWI process in a naturally fractured reservoir having five producing wells and five injector wells completed in an Arab carbonated formation containing light crude oil (API = 42 deg). For this aim, a small pilot oil field was selected with water injection facilities and naturally producing oil wells and all data were collected from the field tests. During a five years' field test, the primary observations at the onset of shutdown periods of the water injection system revealed a repeatable significant enhancement in oil production rate by a factor of plus 5% leading us to assess the application of CWI. This paper represents the significant parameters of pressure and productivity affected during CWI in naturally fractured carbonate reservoirs based upon a dual porosity generalized compositional model. The results hopefully introduce other oil producer companies to the potential of using CWI to increase oil production in conventional water injection systems. The results also outline situations where such applications would be desirable.

Циклическое заводнение бобриковского горизонта Cабанчинского нефтяного месторождения

Циклическое заводнение бобриковского горизонта Cабанчинского нефтяного месторождения

Cyclic Injection Scheme Optimization Research in Gaotaizi Reservoirs of Daqing Oilfield

With the deepening of the oilfield development, oil field has entered the high water cut period. The rate of water cut increasing and production decline are accelerate. It is needed to adjust the way of exploitation in order to improve oilfield exploitation effect. Cyclic water flooding is one of effective means to improve oilfield development effect with the advantages of small investment, quick effect, reduce inefficient output and improve oilfield overall development benefit. In this paper, we use the means of numerical simulation to study the injection timing and reasonable working systems of different types of Wells. Technical basis is provided for further study and field test.

Optimization Research on Cyclic Waterflooding in Low Permeability Fractured Reservoir

Three cyclic waterflooding programs were designed to compare with the original program of block Bao14 according to the characteristics with residual oil. The results showed that the recovery percentage of three designs increased in different level. The fourth design was best. The stage cumulative incremental oil production was 16.07×104t and recovery ratio improved 2.14% than that of original design

An Analytical Model for Brine-Induced Oil Recovery

An analytical model for field application of improved waterflooding through brine concentration is presented. Based on several laboratory studies, many researchers suggested that changing the brine concentration during waterflooding offered viable options for improved oil recovery. In this regard, particularly in cyclic waterflooding, these studies have confirmed the effectiveness of such an approach. Generally, however, they are limited to laboratory studies without much field application. Most laboratory results do not present a clearly defined approach for practical application. This article analyses laboratory results and proffers a concise approach for field application. To this end, based on the reinterpretation of the Civan and Knapp model, an oil recovery model is developed for cyclic waterflooding. This model monitors waterflood performance based on the impact of brine injection for increased oil recovery.