High Water Cut Period Research Articles

Evolution Law of Dominant Flow Channel and Enhanced Oil Recovery Measures for Water Flooding in Reservoirs with Partially Sealed Faults.

The presence of strongly sealed faults can divide a reservoir into complex fault blocks, while partially sealed faults can be created by farewell faults within each block, leading to more intricate fluid migration and residual oil distribution. However, oilfields often overlook these partially sealed faults, focusing instead on the entire fault block, which can impact the efficiency of the production system. In addition, the current technology struggles to quantitatively describe the evolution of the dominant flow channel (DFC) during the water-flooding process, especially in reservoirs with partially sealed faults. This limits the ability to formulate effective enhanced oil recovery measures during the high water cut stage. To address these challenges, a large-scale sand model of a reservoir with a partially sealed fault was designed, and water flooding experiments were conducted. Based on the results of these experiments, a numerical inversion model was established. By combining percolation theory and the physical concept of DFC, a new method was proposed to quantitatively characterize DFC using a standardized flow quantity parameter. The evolution law of DFC was then studied, considering the variations of volume and oil saturation of DFC, and the water control effect of different measures was evaluated. The results revealed that, during the early stage of water flooding, a vertical uniform dominant seepage zone formed near the injector. As the water was injected, DFCs from the top of the injector to the bottom of the producers gradually formed in the unoccluded area. However, DFC was only formed at the bottom in the occluded area. During water flooding, the volume of DFC in each area gradually increased and then tended to stabilize. The development of the DFC in the occluded area lagged behind due to gravity and fault occlusion, leading to the formation of an unswept area near the fault in the unoccluded area. The volume of the DFC in the occluded area was the slowest, and the volume was the smallest after stabilization. Although the volume of the DFC near the fault in the unoccluded area grew the fastest, the volume was only higher than that in the occluded area after stabilization. During the high water cut period, the remaining oil was mainly distributed in the upper part of the occluded area, the area near the unoccluded fault, and the top of the reservoir in other areas. The plugging of the lower part of the producers can increase the volume of DFC in the occluded area, and the DFC moves up throughout the entire reservoir. This improves the utilization degree of the remaining oil at the top of the entire reservoir, but the remaining oil near the fault in the unoccluded area remains inaccessible. The combination of producer conversion, drilling infill wells, and producer plugging can alter the injection-production relationship and weaken the occlusion effect of the fault. The occluded area forms a new DFC, leading to a significant increase in the recovery degree. The deployment of infill wells near the fault in the unoccluded area can effectively control the area and improve the utilization of the remaining oil.

Corrosion Inhibitor Distribution and Injection Cycle Prediction in a High Water-Cut Oil Well: A Numerical Simulation Study

The wellbore downhole strings corrosion has attracted extensive interest as most of the oilfields in China enter the high water-cut period. Injection of corrosion inhibitors, one of the most effective corrosion protection methods, is employed to mitigate the wellbore corrosion. Nevertheless, its wider application suffers from insufficient knowledge regarding the distribution of corrosion inhibitors inside the tubing, particularly with different inhibitor injection cycles. Thus, in this study, the computational fluid dynamics (CFD) method was first attempted to investigate the hydrodynamics in a tubing and the interactions between the corrosion inhibitor and produced fluid with high water-cut. Key factors including the time, wellbore heights, injection rates, oil phase velocities and corrosion inhibitor viscosities were discussed in detail as regards how they affect the corrosion inhibitor distribution inside the tubing. Feasible formulas were established for predicting the volume fraction of the corrosion inhibitor at different wellbore heights, which showed good agreement with the simulation results. It is noted that the determination of the corrosion inhibitor injection rate depends on both the film quality of the corrosion inhibitor and the stability of the annular flow. Based on the interphase diffusion effect, a new method for determining the intermittent injection cycle of corrosion inhibitor was proposed to maintain the integrity of corrosion inhibitor film at the tubing inner wall.

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.

Analysis of development status and adjustment method of a block

Since a certain block was put into development, it has always put improving the injection production relationship and improving the ultimate recovery factor in the first place. Through a series of infill adjustment, supplement and extended drilling, the injection production relationship of single sand body has been gradually improved. In high water cut period, the remaining oil distribution has been quantified through joint multidisciplinary research, and the fluid production structure has been adjusted by combining the oil well injection, hole filling, drilling and other measures, Hard and stable production in high water cut stage is realized. However, due to the small scale of sand body development and fault development, the contradiction between single sand body injection and production is still prominent. From the perspective of development effect of Gaotaizi old area, compared with Xingnan development area, the degree of recovery at the same water bearing stage is obviously low, and the development effect is poor. At present, the comprehensive water cut has reached 92.77%, and the recovery percentage is only 28.05%. The research shall be based on the results of fine reservoir description, guided by the results of multidisciplinary research, and focus on the comprehensive analysis and sorting of the injection production relationship of single sand body through the re understanding of geology, so as to find the adjustment potential of supplement and injection conversion. Through the adjustment of the injection production system, increase the water injection well points, expand the swept volume, improve the degree of water drive control, so as to increase the formation pressure and improve the development effect of the block.

Optimization of Injection Parameters for Profile Control and Flooding in an Oilfield during High Water Cut Period

Optimization of Injection Parameters for Profile Control and Flooding in an Oilfield during High Water Cut Period

Adjustment and tapping technology of water drive reservoir in late high water cut period

The implementation of oilfield development technology is closely related to geological conditions. Scientific and reasonable exploitation strategy is of great significance to improve oilfield economic benefits and technical utilization rate. At present, the development of oilfield is in the middle and late stage, and there are still many problems in technology, which need to be adjusted and innovated urgently. According to the geological conditions of oil fields and the current intensive exploitation technology, it is pointed out that in the late development of high water cut, it is an important method to improve the economic benefits of oil fields by using the potential tapping technology. In ORDER TO REALIZE THE TRANSFORMATION OF oil and gas exploration technology, THE key LIES in increasing research and development, accelerating technology innovation and application, and pushing oil field development into a new development track.

Study on Characteristics of Phase Permeability Curve of Xingbei Development Zone During Extra High Water Cut Period

The relative permeability curve is an important basic data for the preparation and dynamic analysis of oilfield development ( adjustment ) schemes. Due to the different types of relative permeability curves in different water cut stages, there is a large deviation in the prediction of oilfield development indexes in the ultra-high water cut stage according to the relative permeability curve in the early stage of development. In order to study the change of relative permeability curve in the development process, based on the analysis of the morphological characteristics of 118 relative permeability curves in the ultra-high water cut stage of 28 coring wells in Xingbei development area after more than 50 years of water injection development, the influence of injection multiple on the relative permeability curve, and the influence of long-term water injection development on the average pore radius, the changes of morphological characteristics and characteristic parameters of relative permeability curves after entering the ultra-high water cut stage were studied, and a correction method for the changes of oil phase and water phase of relative permeability curves according to the changes of relative permeability curves in different water cut stages was proposed to better reflect the changes of relative permeability curves in the whole process of water injection development. It provides a basis for accurately predicting the index of water injection development oilfield.

EMD-based multi-algorithm combination model of variable weights for oil well production forecast

Oilfields in high or ultra-high water-cut period are of high nonlinearity and heterogeneity, thus complicated in its internal physics mechanism. Corresponding production data is often of small amount due to large timesteps. In addition, numerous mechanism factors that are usually a prerequisite for traditional data-driven prediction methods are to be determined with extra human effort on a well basis, deviating from the intention of oilfield digital transformation. In response to these obstacles, this research proposes an EMD (Empirical Mode Decomposition)-based variable-weight combination model algorithm (EMD-Combined model): It does not require inputs other than its own historical oil production time series, but rather automatically constructs and filters input features via EMD, time-lag reconstruction and Spearman correlation analysis instead. A dynamic Variable-Weight Combination Methods of four machine learning models with different strengths is constructed to carry out prediction. Experimental results show that the EMD-Combined model is more accurate than the solely use of any of the four single models listed above, or models solely exerted with EMD without model-wise combination. In terms of the ease of usage, deployment and “stability” of prediction quality, EMD-Combined model offers a possibility of improvement in real-life practice.

A New Relative Permeability Characterization Method Considering High Waterflooding Pore Volume

In the process of waterflooding development, high waterflooding PVs will make the fluid percolation in the reservoir more complicated, resulting in lower efficiency of waterflooding. High waterflooding PVs will affect the relative permeability and change the seepage law of oil–water two-phase flow in a high water-cut period. In this study, we performed high waterflooding PVs relative permeability experiments using nine natural cores. The unsteady measurement method is used to test the relative permeability curve. The results show that: (1) the relative permeability is affected by the waterflooding PVs, the recovery efficiency of 2000 waterflooding PVs is 10.72% higher than that of 50 waterflooding PVs on the core scale; (2) it makes water mobility increase sharply, while oil phase flow capacity remains low and decreases at high water cut stage. A new relative permeability characterization method considering high waterflooding PVs is established, which is applied to the numerical simulator. It shows that the remaining oil saturation of the high-permeability belt is higher than the calculation results of the traditional numerical simulator. It means that the injected water does not diffuse much into the low-permeability zone of the formation. The modified simulator is validated with the actual China offshore oilfield model. The numerical saturation of the key section of the passing well is in good agreement with the actual logging interpretation results, and the water cut curve fits better in the whole area. The modified simulator could predict oil production accurately after high waterflooding PVs treatment.

Optimization of Sensitive Technical Parameters of Water Alternating Gas Injection Displacement Based on Multi-indicator Orthogonal Design

In view of a series of comprehensive problems such as the limited space of conventional water displacement, the low-pressure maintenance level, and the greater contradiction during the high water cut period of 64-20 sub-block, the development potential of its conversion medium with carbon dioxide was evaluated. After determining that water alternating gas injection displacement was the dominant development method in the target area, the sensitive parameters were optimized based on multi-indicator orthogonal design, numerical simulation and comprehensive scoring. The research results show that the use of water alternating gas injection displacement in the high water cut period could better maintain the formation pressure and greatly increase the recovery percent. It has a large application potential in the target area and the final optimal parameters are as follows: gas injection time is 20 years, cycle is 8 months, velocity is 1 × 104 m3/d, gas-water ratio is 1 : 1 and bottom hole flowing pressure is 13 MPa. And the technical parameters of velocity and cycle have the most important contribution to the displacement effect during the high water cut period in the earlier period.

Research and Application of Countermeasures for Tapping Potential of Remaining Oil in High Water-cut Period of Waterflooding Reservoir

Research and Application of Countermeasures for Tapping Potential of Remaining Oil in High Water-cut Period of Waterflooding Reservoir

Study on optimal combination of stratified water injection in extra high water cut period

After several decades of mining, the block has entered the development stage of ultra-high water cut. Although the encryption adjustment and subdivision adjustment for different mining objects have been completed, the interlayer interference is still serious and invalid cycle still exists, making it difficult to develop and adjust. The subdivision adjustment of water injection well can further improve the production degree of various oil layers, effectively improve the utilization rate of water injection, and realize the adjustment of water injection well profile and water injection structure, which is one of the measures with low investment that can effectively improve the development effect of water flooding. To satisfy the needs of the reservoir, fine reservoir, operation based on the production dynamic data and based on the analysis of monitoring data, the application of multidisciplinary reservoir description technology, quantitative analysis of thin layered segment permeability variation coefficient, monolayer onrush of small layer in the paragraph number, interval number, sandstone thickness influence on subdivision adjustment effect, analysis of well test cycle and operation costs influence on economic benefits, A series of combination parameters of subdivision water injection interval are obtained, which can guide the subdivision water injection program, effectively alleviate the range of production decline and water cut rise, and provide technical support for fine tapping potential of water flooding in ultra-high water cut period.

Study of Fine Management Mode on Improving Potential Benefits of Measures

The oil field has entered the extra high water cut period, the oil well fracturing and oil increment have made great contributions to the fine tapping potential of water flooding. At the same time, the oil well fracturing and oil increment production has become an important part of the stable production of water flooding. Therefore, the fine oil well fracturing management mode and the improvement of oil well fracturing and oil increment effect are particularly important. Focus from the advance potential survey, the implementation of pre-pressure training; fine well selection and layer selection, optimize fracturing design ; strengthen process management, strengthen construction supervision; do well after fracturing management, improve oil increment effect to fine oil well fracturing management mode. The comprehensive application of various technical means to continuously improve the accuracy of residual oil analysis is the basis to ensure the targeted fracturing measures; on the basis of the analysis of remaining oil, it is the prerequisite and necessary guarantee to improve the fracturing effect and prolong the effective period to do well in the preinjection and post-injection recharge. The key to improve the fracturing effect of oil well is to combine the remaining oil potential and fracturing technology closely, design personalized scheme, refine the fracturing interval and expand the construction scale. Doing well in fracturing process management and refining each construction link is an effective guarantee to maximize the benefits of measures. On measures to tap potential, deepen potential research, optimize program design, give full play to the synergistic effect of measures, and strive to improve the pertinence of measures to tap potential in ultra-high water cut period, continuously improve the fracturing effect, improve the benefits of measures to tap potential, and achieve the goal of ' high efficiency, sustainable and guaranteed’ sustainable and stable production.

Study on technical measures to improve oil recovery during extra high water cut period

China’s petroleum resources are mainly continental facies with high petroleum density. Due to high heterogeneity, mining by traditional methods is not effective, and nearly half of the resources are not developed. The onshore oil fields that have been developed in Daqing area; Liaohe, Shengli and other large oil fields have entered high water cut stage, but there are still a lot of problems such as scattered remaining oil distribution, flooded reservoir, low recovery factor, reduced production and poor economic benefits. Based on this, this paper mainly analyzes the related technical measures to enhance oil recovery in the ultra-high water cut period.

Blocking characteristics of high water-cut crude oil in low-temperature gathering and transportation pipeline

High-pour point and high-viscosity crude oil can be gathered and transported below the pour point during a high water-cut period. However, oil under these conditions can easily aggregate, thereby blocking the pipeline. In this study, a comprehensive field experimental pipeline system (368 m long and 64 mm internal diameter (ID)) was developed to investigate the pipeline blockage mechanism. The changes in the pressure, temperature, and oil–water morphology during cooling experiments were studied. The pipe flow regime under different flow rates of water-blending conditions was divided into blockage, transition, and safe operation modes. The blocking mode was divided into stable development, rising volatility, and fast congestion periods. The rheological change of non-Newtonian crude oil during the cooling process was the dominant mechanism of blockage that caused successive decreases in the oil–water interface until the water phase channel was blocked, finally causing a surge in the flow resistance and pressure drop. The correlation equation of the single well temperature limits as functions of fluid flow rate and water-cut was established, and the error between the prediction results and experiments was between 0.12–0.20 °C. The prediction method for the minimum water-blending flow rate was combined with heat transfer analysis, and the corresponding temperature limit was less than the pour point of crude oil at approximately 1–10 °C (liquid flow rate: 5–30 m3/d, water-cut: 80%–90%). The investigations conducted in this study further ascertained the crucial impact of non-isothermal and non-Newtonian characteristics on the low-temperature oil–water two-phase flow.

Research and application of the potential tapping method of single sand body in a high water cut period

This paper studies the reservoir sedimentary system of an oilfield, grasps the origin and characteristics of sand development in narrow and small river channels, and uses the method of sandstone facies determination to track and predict sand bodies, and establishes the continuous distribution mode of channel sand bodies. On this basis, combined with the dynamic monitoring data, the type and potential of remaining oil in the oilfield are analyzed by using the dynamic analysis method, and five potential tapping directions centered on the channel sand body are determined. The practice shows that the remaining oil analysis based on the anatomy of single sand body should be paid more attention to in the exploration of potential in high water cut period. Combined with various technical means such as reinjection, encryption and orientation, the injection production relationship of single sand body should be improved and the field application has achieved good results.

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.

Investigation on Washing Condition of Reservoir in Region A

At present, A oilfield is in the extremely high water-cut period, and it is the key to realize the distribution of residual oil potential. Through the data analysis of the sealed coring well, this is one of the most intuitive and reliable methods for residual oil distribution. The changes and growth of water wash thickness of various oil layers can be understood and analyzed, and the evolution process of oil formation status can be clearly seen with the deepening of oilfield water injection development and the infilling and adjustment of well pattern. The results show that the area is in the condition of medium water washing and still has great potential. The washing degree of one kind of oil layer is high, mainly medium and strong washing. The weak and unwashed oil layers are mainly concentrated in the second and third oil layers, which are the target of the next adjustment and exploration. According to the distribution of residual oil in the second and third oil layers, the next step is to optimize the adjustment of injectionproduction well pattern and the modification of cooperation measures. For improving the level of weak and unwashed reservoirs, it is of guiding significance for the subsequent development of reservoirs in the ultra-high water-cut period.

Micro-scale investigation on the effect of waterflooding rate on oil recovery and residual oil distribution

Waterflooding is currently one of the most common and mature oil and gas development methods. However, when oil and gas fields enters the medium or high water-cut period, there is still a large amount of residual oil remaining untapped while residual oil characteristics and distribution could be complicated. Micromodel method is considered as a novel experimental method for studying residual oil characteristics and waterflooding. Unlike conventional core flooding, visualization of the whole process can be realized through micromodels. In this work, three different flooding rates were used to simulate the waterflooding process via micromodels. Consequently, oil recovery rates and residual oil distribution were obtained. It was observed that higher waterflooding rate increased the oil recovery. When the flooding rate was large, dispersed residual oil was observed after waterflooding. When the rate was small, residual oil exhibited more complicated configurations. For the trapped residual oil in the dead end pores in hydrophilic rock matrix, increasing the flooding rate or the viscosity of displacing phase could be beneficial to dislodge the residual oil.

Research and application of pressure decreasing technology of polymer material injection wells

Injecting polymer materials is an important means to improve the ultimate recovery, maintain stable production and improve the development effect of the oil field in the high water cut period. However, in the development process of polymer flooding, with the continuous increase of the cumulative polymer injection, the problem of high-pressure under-injection frequently occurs in the injection well. In this paper, based on geological characteristics and plugging material analysis, the causes of high pressure/under-injection and production characteristics of different types of measure wells. To study and optimize the rubber breaking, degradation and synergistic acidification liquid system that are applicable to different blockage conditions can effectively improve the adaptability of the blockage liquid system; Meanwhile, the formation of a quick plugging process with the characteristic of “single-stage single-step injection + prescription formula structure” can effectively improve the success rate of polymer plugging process measures, providing strong technical support for polymer flooding technology.