Extra High Water Cut Stage Research Articles

Study on enhanced oil recovery improvement of fractured tight reservoir at extra high water cut stage

Study on enhanced oil recovery improvement of fractured tight reservoir at extra high water cut stage

Research and Practice on Implementing Segmented Production Technology of Horizontal Well during Extra-High Water Cut Stage with Bottom Water Reservoir

Bohai X oilfield has reached the extra-high water cut stage of more than 95%, dominated by the bottom water reservoir. The oilfield mainly adopts horizontal-well exploitation, with the characteristics of high difficulty and low success rate for well water plugging. To solve the above problem, the segmented production technology of horizontal wells was developed to guide oilfield applications and tap their potential. In the segmented design stage, the horizontal section is objectively segmented by drilling condition analysis, optimally based on drilling through interlayers or permeability discrepancy formation, simultaneously combined with the numerical simulation method. When implementing measures, annulus chemical packer materials are squeezed between segments to effectively inhibit the fluid flow between the open hole and the sand-packing screen pipe. Moreover, the packers are used to seal between segments to effectively restrain the flow between the screen and the central tube, achieving the establishment of compartments. In the production process, the valve switch on the central tube can be independently controlled by a remotely adjustable method to achieve optimal production. This segmented production technology was successfully tested for the first time in Bohai oilfield. Up to now, a total of six compartment measures have been implemented, remarkably decreasing water cut and increasing oil production for horizontal wells in the bottom water reservoir. This method does not require water testing, and the optimal production section can be chosen through segmented independent production, greatly improving the success rate of water-plugging measures for horizontal wells. This technology opens up a new mode for the efficient development of horizontal wells in bottom water reservoirs and is planned to be widely promoted and applied in similar oilfields.

Improve Oil Recovery Mechanism of Multi-Layer Cyclic Alternate Injection and Production for Mature Oilfield at Extra-High Water Cut Stage Using Visual Physical Simulation Experiment

In order to achieve sustainable development of mature oilfield, a series of adjustment measures should be implemented to improve production performance at the extra-high water cut stage. South Kumkol reservoir is a typical multi-layer low viscosity oil reservoir, which has the characteristics of small sandstone body, high shale volume, and strong heterogeneity. At present, the water cut of the South Kumkol reservoir is about 90%, which is on the verge of being abandoned. Multi-layer cyclic alternate injection and production (MCA-IP) is an ideal adjustment measure for multi-layer oil reservoir to improve oil recovery (IOR) at the extra-high water cut stage. In this paper, we designed the double-plate visual physical device and the MCA-IP experimental program and then calculated the sweep coefficient using image recognition method. Furthermore, the sweep coefficient was quantitatively calculated by image recognition method. The results show that the sweep area extends to both sides of the main streamline and the sweep efficiency is gradually improved after the completion of MCA-IP. In addition, the IOR mechanism of MCA-IP mainly includes reperforation, well-pattern encryption, and asynchronous injection-production. The reperforation and well-pattern encryption increased the sweep coefficient by about 19.52%, while asynchronous injection-production increased the sweep coefficient by about 1.2%, and the overall sweep coefficient increased by about 20.7%. According to the experimental data statistics, the MCA-IP method can increase oil recovery by about 11% and reduce water cut by about 6%.

Research and application of profile control and water shutoff technology in fractured sandstone reservoir based on system analysis method

Huoshaoshan Oilfield is a sandstone reservoir with severe heterogeneity. After years of enhanced water flooding, the reservoir conditions have changed greatly. Based on the research results of fine reservoir description, the key to successful industrial application of large-scale water shutoff and profile control is to select suitable water shutoff and profile control agents and improve injection technology and evaluation technology. This technology has become a leading technology for improving water flooding recovery in the development of extra-high water cut stage in Huoshaoshan Oilfield, with remarkable economic benefits. In this paper, the main factors affecting the performance of pre-gel system and the flow experiment used to test its performance index are described by systematic analysis method, and the construction effect of well group H1194 is briefly introduced.

基于特高含水期相渗规律的含水率预测新模型

基于特高含水期相渗规律的含水率预测新模型

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.

A New Method of Predicting the Distribution of Remaining Oil by the Composite Index of Heterogeneity

As the Xingbei Development Zone gradually goes into the extra high water cut stage, the difficulty of residual oil tapping is becoming harder and harder. Heterogeneity not only controls the injection agent’s sweep coefficient, but also controls the injection displacement efficiency, which is the key factor affecting the formation and distribution of residual oil.Characterization of reservoir macroscopic heterogeneity by parameters such as sedimentary microfacies, oil layer structure, permeability, porosity and net thickness ratio. The heterogeneous comprehensive index obtained by the wave superposition method can not only quantitatively evaluate reservoir heterogeneity, but also explain the distribution characteristics of the residual oil.Using this method to fit the eastern part of a district of Xingbei Oilfield, The obtained heterogeneous composite index (IRH) distribution map is compared with the reservoir numerical simulation residual oil saturation map, and the correlation between the two is good. Statistically fit the production of new wells in the simulated area, wells with heterogeneous composite index between 0.55 and 0.75 have higher cumulative oil production, average daily oil production, and the water content is 2-5 percent lower than the average. According to the comprehensive analysis, the remaining oil enrichment area is in the IRH [0.55, 0.75] region. Guided by this method, we repart Well B1; let free its S II 8 accompanying water blocking layer, so as to strengthen liquid supply to Well B2 and Well B3, which are rich in residual oil through this method. The production plan proves to be effective, Well B2’s daily oil production increases by 1.5t, and Well B3’s daily oil production increases by 1.2t. Till now, the accumulated increasing oil production has up to 1324t, which equals to economic benefits of 3840,000 RMB.Through quantitative characterization of reservoir heterogeneity, we find that the remaining oil enrichment zone is mostly located in the IRH [0.55, 0.75] region, which has important guiding significance for the future development.

Study on the method of improving fracturing effect by waterflooding in extra high water cut stage

After the oil field enters the stage of “double ultra-high” development, the development potential turns to the reservoir with worse development, and it is more difficult to identify the remaining oil. In order to meet the requirements of potential tapping under the new situation and achieve accurate potential tapping, the conventional fracturing technology has been continuously developed and improved by strengthening the analysis of remaining oil, optimizing the scheme design and other methods, effectively making up for the decline of production of old wells. At the same time, on the basis of conventional fracturing technology, aiming at the characteristics of reservoir and well pattern, the new high-efficiency fracturing technology represented by fracture controlled sand body fracturing and three types of reservoir pressure flooding is explored, which realizes the breakthrough of low production well productivity in poor reservoir and expands the fracturing technology.

Well Pattern Modification and Injection-production Optimization for Extra-high Water Cut Oilfield

The extra-high water cut stage is still an important stage of oil production. In order to develop the oilfield in this stage, a reservoir model was established using the geological and production history data of a block in Shengli Oilfield. Based on the history matching result, the numerical reservoir simulation of the modification was carried out from row injection well pattern to different well patterns. On the basis of residual oil distribution, balanced injection-production and formation pressure distribution, the optimal well pattern for this block was optimized. The well spacing for different well pattern was also simulated. The optimal well spacing was determined by the net present value (NPV) method, and the timing of well pattern modification was determined by the relationship between NPV peak and water cut. Latin hypercube sampling method was used to design the injection-production parameter schemes. The optimal injection and production parameters range of row and nine point well pattern was determined respectively. This research results can be used for reference in the development and adjustment of similar oilfields in the extra-high water cut period.

Pore-scale investigation of residual oil distributions and formation mechanisms at the extra-high water-cut stage

Water flooding has been widely applied in the oilfield development as a secondary recovery method due to its effectiveness and economic feasibility. After several decades of production, numerous oil fields are normally entering into the extra-high water-cut stage (water cut higher than 90%). The extra-high water-cut stage takes an extremely important role in the whole development process since a large amount of residual oil remains trapped in reservoirs (approximately 50% to 60% of initial oil in place) at this stage. The extensively continuous distribution of subsurface oil at the low water-cut stage has changed greatly after the water cut of mature oilfields becomes over 90%. The residual oil distributes mainly in a scattered state at the extra-high water-cut stage, while water flows in a continuous state. Oilfields with high water cut are normally suffering from poor flooding efficiency, to improve water flooding efficiency, it is necessary to understand distributions and formation mechanisms of residual oil at the extra-high water-cut stage. In this study, a pore-scale simulation model is developed to exploit the potential of residual oil in a porous media. A direct numerical simulation method is employed to simulate fluid flow in a porous media, the position of interface between water and oil is determined by the phase field method. The capacity and accuracy of the model is validated by a classical benchmark: a layered two-phase flow with a variable viscosity ratio. The formation processes of residual oil and mechanisms behind this are investigated in terms of mechanics. The results show that the residual oil in porous media at the extra-high water-cut stage can be classified as five types, namely, isolated oil droplet, residual oil in pore throats, cluster residual oil, oil film and residual oil in dead end. Rock configuration, wettability and capillary pressure play important roles in the formation of residual oil. The formation of isolated oil droplet is dominated by rock configuration, capillary pressure and wettability. Capillary pressure and wettability are key factors for the formation of residual oil in pore throats. Rock configuration and capillary pressure are responsible for the formation of cluster residual oil. Wettability is the dominant factor for the formation of oil film. The relationship between cumulative water production and cumulative oil production is consistent at the pore scale and Darcy scale. Relative permeability curve is obtained based on the pore-scale simulation and an upward turning is observed after the water cut reaches 98%. Increasing injection velocity and injection of surfactant can both displace cluster residual oil, residual oil in pore throats and isolated oil droplets, which leads to the increase in oil recovery at the extra-high water-cut stage. The decline in cluster residual oil is the main contributor to rise in oil recovery. Times of increasing injection velocity have an important pact on the field development. This study is only conducted in a two dimensional porous media, and more factors (e.g., gravity) should be incorporated into our model to investigate the formation process of residual oil in the three dimensional porous media.

Research on microscopic oil displacement mechanism of CO2 EOR in extra-high water cut reservoirs

In China, CO2 EOR technology is mostly applied in small scale field test after water flooding. Microscopic mechanism of CO2 EOR at extra-high water cut stage is not clear to us. Based on the characteristics of residual oil after water flooding, three types of ideal core models were designed including dead-end model, shaped island model and cluster model. The microscopic experiments were carried out in high temperature high pressure micro-visualization experiment apparatus of independent research and development. The microscopic mathematic model of CO2-water-oil interaction was established. The process of CO2 dissolution and extraction during CO2 injection at extra-high water cut stage (water cut>98%) were monitored in the experiments for the first time. The microscopic mechanism of CO2 EOR on trapped oil droplets and the influence of water barrier on miscible displacement were discussed. The results from experiments and mathematic calculation conclude that water barrier should postpone and complicate miscible process between CO2 and trapped oil. No matter how thick the water film, CO2 can diffuse through the water film into the trapped oil. The higher injection pressure is, the faster CO2 diffuses into oil, the more easily miscibility is achieved. CO2 miscible displacement contributes to oil recovery largely after water flooding. CO2 EOR might benefit from the increasing of injection pressure and the full contact time between CO2 and fluid (water and trapped oil) underground in extra-high water cut reservoir.

Micro-distribution and mechanical characteristics analysis of remaining oil

As the water drive reservoir enters extra high water cut stage (greater than 80%), remaining oil distribution becomes increasingly dispersed. Research on micro residual oil in pore appears particularly important for reservoir development at extra high water cut stage. Oil occurrence characteristics recognition helps to understand the distribution of remaining oil and the mechanical characteristics of oil is the guide for tapping the remaining oil. On the basis of pore scale oil–water two phase flow experiments, micro distribution of remaining oil is divided into four occurrence states in accordance with oil features at different stage of water flooding, the flake of remaining oil, oil column, oil droplet and oil film. A quantitative characterization method of remaining oil occurrence states is established. By using micro numerical simulation method, change rules of four occurrence states of remaining oil during the process of water displacement and the mechanical characteristics of different occurrence state of remaining oil are analyzed. Results show that the continuous oil phase gradually transforms to discontinuous phase and even to dispersed phases during the water flooding process. At extra high water cut stage, most of remaining oil are dispersed oil columns, oil droplets and oil films, which are the main target of remaining oil to be tapped. By changing water flow direction or increasing the displacement pressure gradient, the surface adsorption force acting on oil columns are overcome, and then the oil columns begin to move and finally to be produced out. Oil droplets in pore-throat center are scoured and carried out by water as the increase of the injection volume, while the oil droplets in blind ends and the oil films are extracted out by adding chemicals to reduce the interfacial tension, so as to enhance oil recovery. For water flooding reservoir, the corresponding tapping measures for four types of oil occurrence states brought forward have great meanings of improving reservoir recovery at high water cut stage.

Ensemble-based optimization of interwell connectivity in heterogeneous waterflooding reservoirs

Estimation of interwell connectivity is of great importance to optimization of injection-production scheme and decision-making of potential-tapping strategies during the later stage of waterflooding. However, the traditional reservoir simulation requires detailed information of various reservoir/fluid parameters, which is time-consuming and difficult to obtain the reliable estimates due to large uncertainties. The capacitance-resistance model inferred from field injection and production data provides an attractive alternative to understanding the interwell connectivity relationship and close-loop reservoir management. For this study, the producer-based and injector-producer pair-based capacitance resistance model, CRMP and CRMIP, are employed to compute liquid production rate of each producer, respectively, followed by description of observed water cut data using the Koval fractional-flow equation. Then, this paper proposes a novel framework that enables the newly developed Stochastic Simplex Appropximate Gradient (StoSAG) algorithm to optimize interwell connectivity in waterflooding reservoirs by preconditioning the hybrid nonlinear constraints, which is further validated by a heterogeneous synthetic case. The results show that, compared to the projected-gradient (PG) and EnKF methods, the StoSAG optimization technique can handle the sequential data assimilation in large-scale nonlinear dynamics more robustly; due to more degrees of freedom, the CRMIP representation captures the reservoir's dynamic behavior better than CRMP, resulting in a more satisfactory estimation of geological parameters relative to each reservoir control volume; The Koval fractional-flow equation are effective to represent the water-producing characteristics from small-to-large water cut period, but a great deviation will be caused during the extra-high water cut stage (fw>90%) because of its inherent drawbacks.

STUDY ON THE RATIONALITY OF FLOW UNIT DIVISION IN Y OILFIELD

Employing the research for and exploitation of remaining oil into division of flow unit in oilfield, especially for which enters extra high water cut stage mining stage oil. This paper selects permeability and porosity as parameters, and uses the cluster analysis method, to divide flow unit in Y oilfield through the SPSS software. Results show that coincidence rate of division of flow units in the liquid producing profile reach 75%, and the load rate of the dynamic water injection reached 82%, therefore it illustrates the division of flow units is reasonable. Meanwhile It provides a reference to improve development effect later.

Water Displacement Rule at Extra-High Water Cut Stage

During the development of the oilfield, the water cut of the water controlled field is an aggregative indicator which is affected by various factors. It can reflect the restriction of liquid flowing rules from the oil layer and crude oil physical property, and the effect of serious technical measures during the exploitation. Water cut increasing rate is closely related with water cut. The level of water-cut increasing rate of various well network was evaluated during oil producing with extra-high water cut in Xingnan development area, compared the differences among various well networks, and analyzed the geology causes and development causes.

Application of Multivariate Regression Method in the Prediction of Oilfield Development Indexes

Currently most of our oil fields have entered the extra high water cut stage. Accurate prediction of field development dynamic is the foundation of the reasonable, efficient, sustainable oil field development. Prediction of oilfield development index have varieties of methods ,including the law of diminishing water flooding Union law solution, yield component method, multiple regression and so on. In this paper, we take xingnan development zone eight to twelve district extension well network development index prediction as an example, introduces the application of multiple regression method in the prediction of reservoir indicator.

The Temperature Field Distribution in Thermal Recovery and the Study on Residual Oil Distribution Laws

Western Bei II Area in Saertu Oilfield, Daqing Oilfield is the test area. It has now entered an exploitation phase of extra high water cut stage. Under the circumstance of a long time of development and complex conditions of well history in this area, it has experienced water flooding, polymer flooding and thermal recovery. Based on basic geological characteristics in the test area, this study establishes three-dimensional geological static models and conducts the fine reservoir numerical simulation of the test area. In addition, it summarizes the temperature field distribution features before and after the thermal recovery as well as causes and distribution laws of the residual oil, which provides a reliable basis for development, deployment and measures to adjust in the next step in oilfields.

Research on Evaluation about Measures with Water Plugging in the West of Bei 3 Area of Daqing Saertu Oilfield

Measure of plugging water refers to through sealing high water formation to slow down the contradiction between lays, so as to increase the liquid production of low water formation and to increase the swept volume the extent of reserves producing. It is an important measure that aims at the rapid increasing of liquid-oil ratio in late stage of high water-cut, to keep the stable production of oil field. It is an effective measure to reduce and control the useless water production rate which not only can increase the fluid production sensibly but also can slow down the production decline and guarantee the economic rationality in oilfield development. Field practice has proved that the measure of plugging water has a better guiding significance to the reservoir in late high or extra high water-cut stage. Through analyzing the effect of plugging water, and a comprehensive evaluation of the effect of plugging water, we can find out the key factors that affect the measures of plugging water, which has a better guiding significance to maximize the high water cut oilfield development profit.

The Sediment Group Evaluation Index System of Extra High Water-Cut Stage in Waterflooding Oilfield Reservoir

For reserviors which have multiple pay zones, various types and severe heterogeneity, it is China's successful experience of waterflood development to implement layered waterflooding, layered recovery, layered monitoring, and separated layer stimulation and adjustment. So it is worth paying much more attention on how to judge the rationality of layer series division, and only the layer system is reasonably divided can we obtain a higher recovery. In order to make a comprehensive evaluation of the combination of layer series, this paper has screened and analyzed the main indicators affected by the combination of layer series of development applying the principles of multiple correlation analysis, so that we obtain a comprehensive indicator system of layer series combination evaluation, and this system dose play an important role in reasonable layer series division.