Effect of CO_(2)flooding in an oil reservoir with strong bottom-water drive in the Tahe Oilfield,Tarim Basin,Northwest China

The dissolution and diffusion of CO_(2)in oil and water and its displacement mechanism were investigated by laboratory experiment and numerical simulation for Block 9 in the Tahe oilfield,a sandstone oil reservoir with strong bottom-water drive in Tarim Basin,Northwest China.Such parameters were analyzed as solubility ratio of CO_(2)in oil,gas and water,interfacial tension,in-situ oil viscosity distribution,remaining oil saturation distribution,and oil compositions.The results show that CO_(2)flooding could control water coning and increase oil production.In the early stage of the injection process,CO_(2)expanded vertically due to gravity differentiation,and extended laterally under the action of strong bottom water in the intermediate and late stages.The CO_(2)got enriched and extended at the oil-water interface,forming a high interfacial tension zone,which inhibited the coning of bottom water to some extent.A miscible region with low interfacial tension formed at the gas injection front,which reduced the in-situ oil viscosity by about 50%.The numerical simulation results show that enhanced oil recovery(EOR)is estimated at 5.72%and the oil exchange ratio of CO_(2)is 0.17 t/t.

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

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

Remaining Oil Distribution Law and Potential Tapping Strategy of Horizontal Well Pattern in Narrow Oil Rim Reservoir with Gas Cap and Edge Water

For thin oil rim reservoir with gas cap and edge water, it is helpful to improve the development effect to find out the distribution law of remaining oil in this kind of reservoirs. For this reason, taking the narrow oil rim reservoir with gas cap and edge water of Oilfield A in Bohai Sea as a case, the main controlling factors, including reservoir structure, fault, gas cap energy, edge water energy and well pattern, affecting the distribution of residual oil in this kind of reservoir were analyzed by using the data of core, logging, paleogeomorphology and production. Then, the distribution law of remaining oil was summarized. Generally, the remaining oil distribution is mainly potato-shaped or strip-shaped in plane. Vertically, it depends on the energy of gas cap and edge water. For the reservoir with big gas gap and weak edge water, the remaining oil mainly lies in the bottom of oil column. And for the reservoir with small gas gap and strong edge water, the remaining oil mainly locates at the top of oil column. Aiming at different distribution modes of remaining oil, the corresponding potential tapping strategies of horizontal wells are put forward: in the late stage of development, for the reservoir with big gas gap and weak edge water, the remaining oil concentrates at the bottom of the oil column, and the position of horizontal well should be placed at the lower 1/3 to the lower 1/5 of the oil column;for the reservoir with small gas cap and strong edge water, the remaining oil locates at the top of the oil column, and the position of horizontal well should be put at the upper 1/5 to the upper 1/3 of the oil column height, vertically. Based on the study on remaining oil of Oilfield A, a potential tapping strategy of well pattern thickening and vertical position optimization of horizontal well was proposed. This strategy guided the efficient implementation of the comprehensive adjustment plan of the oilfield. Moreover, 18 infill development wells were implemented in Oilfield A, and the average production of the infill wells is 2.1 times that of the surrounding old wells. It is estimated that the ultimate recovery factor of the oilfield will reach 33.9%, which is 2.3% higher than that before infilling wells. This study can be used for reference in the development of similar reservoirs.

Geochemical characteristics of reservoir after water and polymer flooding in Xingshugang oilfield of Daqing

Collecting 44 oil-sand specimens of Pu-I Member in two inspection wells before and after polymer flooding in the thirteenth district of Xingshugang oilfield,with experimental analysis,the author obtained the data about oil viscosity,flow,oil saturation and oil displacement efficiency.The result shows that viscous oil predominates in the main remaining oil in Xingshugang oilfield after water flooding with a certain amount of low viscosity oil,high viscosity oil and heavy oil;after polymer flooding,the viscous oil is main ingredient.Compared with water flooding,the low mobility and poor oil can be spread by polymer flooding,expanding the affected area and improving sweep efficiency and oil recovery.The geochemical affecting factors of water flooding and oil displacement efficiency refer to reservoir flow,permeability and the viscosity of residual oil.In the reservoir with permeability from low to high,the polymer flooding efficiency is better than water flooding.It provides the basis for improving the water and polymer flooding efficiency of the Xingshugang oilfield.

Factors influencing oil recovery by surfactant-polymer flooding in conglomerate reservoirs and its quantitative calculation method

This study aims to clarify the factors influencing oil recovery of surfactant-polymer(SP)flooding and to establish a quantitative calculation model of oil recovery during different displacement stages from water flooding to SP flooding.The conglomerate reservoir of the Badaowan Formation in the seventh block of the Karamay Oilfield is selected as the research object to reveal the start-up mechanism of residual oil and determine the controlling factors of oil recovery through SP flooding experiments of natural cores and microetching models.The experimental results are used to identify four types of residual oil after water flooding in this conglomerate reservoir with a complex pore structure:oil droplets retained in pore throats by capillary forces,oil cluster trapped at the junction of pores and throats,oil film on the rock surface,isolated oil in dead-ends of flow channel.For the four types of residual oil identified,the SP solution can enhance oil recovery by enlarging the sweep volume and improving the oil displacement efficiency.First,the viscosity-increasing effect of the polymer can effectively reduce the permeability of the displacement liquid phase,change the oil-water mobility ratio,and increase the water absorption.Furthermore,the stronger the shear drag force of the SP solution,the more the crude oil in a porous medium is displaced.Second,the surfactant can change the rock wettability and reduce the absorption capacity of residual oil by lowering interfacial tension.At the same time,the emulsification further increases the viscosity of the SP solution,and the residual oil is recovered effectively under the combined effect of the above two factors.For the four start-up mechanisms of residual oil identified after water flooding,enlarging the sweep volume and improving the oil displacement efficiency are interdependent,but their contribution to enhanced oil recovery are different.The SP flooding system primarily enlarges the sweep volume by increasing viscosity of solution to start two kinds of residual oil such as oil droplet retained in pore throats and isolated oil in dead-ends of flow channel,and primarily improves the oil displacement efficiency by lowing interfacial tension of oil phase to start two kinds of residual oil such as oil cluster trapped at the junction of pores and oil film on the rock surface.On this basis,the experimental results of the oil displacement from seven natural cores show that the pore structure of the reservoir is the main factor influencing water flooding recovery,while the physical properties and original oil saturation have relatively little influence.The main factor influencing SP flooding recovery is the physical and chemical properties of the solution itself,which primarily control the interfacial tension and solution viscosity in the reservoir.The residual oil saturation after water flooding is the material basis of SP flooding,and it is the second-most dominant factor controlling oil recovery.Combined with the analysis results of the influencing factors and reservoir parameters,the water flooding recovery index and SP flooding recovery index are defined to further establish quantitative calculation models of oil recovery under different displacement modes.The average relative errors of the two models are 4.4%and 2.5%,respectively;thus,they can accurately predict the oil recovery of different displacement stages and the ultimate reservoir oil recovery.

Method of moderate water injection and its application in ultra-low permeability oil reservoirs of Yanchang Oilfield, NW China

To explore the method of improving development effect and solving the problem of water breakthrough and water out for ultralow permeability fractured reservoirs, an indoor evaluation method of dynamic imbibition for fracture-matrix system was established taking the Chang 8 reservoir in southern Yanchang Oilfield as a research target. Key factors for the imbibition effect were obtained, an imbibition's rate expression was obtained, a model considering the double effects of imbibition-displacement was built and optimal injection and production parameters for the research area were obtained as well. The results show that an optimum displacement rate that maximizes the oil displacement efficiency exists in the water displacing oil process, and the optimal displacing rate becomes smaller as the permeability decreases. The imbibition displacement efficiency increases as the reservoir quality index and water wettability index of rock become bigger. But the larger the initial water saturation or oil-water viscosity ratio is, the smaller the imbibition displacement efficiency is. The optimal injection-production ratio for the Chang 8 reservoir of southern Yanchang Oilfield is 0.95, and the predicted recovery is 17.2% when the water cut is 95%, it is 2.9% higher than the recovery of conventional injection-production ratio 1.2. By using the moderate water injection technique based on the double effects of imbibition-displacement mechanism, the water injection development effect for the ultra-low permeability fractured reservoirs can be improved significantly.

Research progress and potential of new enhanced oil recovery methods in oilfield development

This paper reviews the basic research means for oilfield development and also the researches and tests of enhanced oil recovery(EOR)methods for mature oilfields and continental shale oil development,analyzes the problems of EOR methods,and proposes the relevant research prospects.The basic research means for oilfield development include in-situ acquisition of formation rock/fluid samples and non-destructive testing.The EOR methods for conventional and shale oil development are classified as improved water flooding(e.g.nano-water flooding),chemical flooding(e.g.low-concentration middle-phase micro-emulsion flooding),gas flooding(e.g.micro/nano bubble flooding),thermal recovery(e.g.air injection thermal-aided miscible flooding),and multi-cluster uniform fracturing/water-free fracturing,which are discussed in this paper for their mechanisms,approaches,and key technique researches and field tests.These methods have been studied with remarkable progress,and some achieved ideal results in field tests.Nonetheless,some problems still exist,such as inadequate research on mechanisms,imperfect matching technologies,and incomplete industrial chains.It is proposed to further strengthen the basic researches and expand the field tests,thereby driving the formation,promotion and application of new technologies.

A novel type curve for estimating oil recovery factor of gas flooding

A novel type curve is presented for oil recovery factor prediction suitable for gas flooding by innovatively introducing the equivalent water-gas cut to replace the water cut,comprehensively considering the impact of three-phase flow(oil,gas,water),and deriving the theoretical equations of gas flooding type curve based on Tong’s type curve.The equivalent water-gas cut is the ratio of the cumulative underground volume of gas and water production to the total underground volume of produced fluids.Field production data and the numerical simulation results are used to demonstrate the feasibility of the new type curve and verify the accuracy of the prediction results with field cases.The new type curve is suitable for oil recovery factor prediction of both water flooding and gas flooding.When a reservoir has no gas injected or produced,the gas phase can be ignored and only the oil and water phases need to be considered,in this case,this gas flooding type curve returns to the Tong’s type curve,which can evaluate the oil recovery factor of water flooding.For reservoirs with equivalent water-gas cuts of 60%-80%,the regression method of the new type curve works well in predicting the oil recovery factor.For reservoirs with equivalent water-gas cuts higher than 80%,both the regression and assignment methods of the new type curve can accurately predict the oil recovery factor of gas flooding.

Evaluation of reservoir environment by chemical properties of reservoir water‒A case study of Chang 6 reservoir in Ansai oilfield,Ordos Basin,China

The Ordos Basin is the largest continental multi-energy mineral basin in China,which is rich in coal,oil and gas,and uranium resources.The exploitation of mineral resources is closely related to reservoir water.The chemical properties of reservoir water are very important for reservoir evaluation and are significant indicators of the sealing of reservoir oil and gas resources.Therefore,the caprock of the Chang 6 reservoir in the Yanchang Formation was evaluated.The authors tested and analyzed the chemical characteristics of water samples selected from 30 wells in the Chang 6 reservoir of Ansai Oilfield in the Ordos Basin.The results show that the Chang 6 reservoir water in Ansai Oilfield is dominated by calcium-chloride water type with a sodium chloride coefficient of generally less than 0.5.The chloride magnesium coefficients are between 33.7 and 925.5,most of which are greater than 200.The desulfurization coefficients range from 0.21 to 13.4,with an average of 2.227.The carbonate balance coefficients are mainly concentrated below 0.01,with an average of 0.008.The calcium and magnesium coefficients are between 0.08 and 0.003,with an average of 0.01.Combined with the characteristics of the four-corner layout of the reservoir water,the above results show that the graphics are basically consistent.The study indicates that the Chang 6 reservoir in Ansai Oilfield in the Ordos Basin is a favorable block for oil and gas storage with good sealing properties,great preservation conditions of oil and gas,and high pore connectivity.

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

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

Advances in enhanced oil recovery technologies for low permeability reservoirs

Low permeability oil and gas resources are rich and have great potential all over the world, which has gradually become the main goal of oil and gas development. However, after traditional primary and secondary exploitation, there is still a large amount of remaining oil that has not been recovered.Therefore, in recent years, enhanced oil recovery(EOR) technologies for low permeability reservoirs have been greatly developed to further improve crude oil production. This study presents a comprehensive review of EOR technologies in low permeability reservoirs with an emphasis on gas flooding, surfactant flooding, nanofluid flooding and imbibition EOR technologies. In addition, two kinds of gel systems are introduced for conformance control in low permeability reservoirs with channeling problems. Finally,the technical challenges, directions and outlooks of EOR in low permeability reservoirs are addressed.

Theories and practices of carbonate reservoirs development in China

Carbonate reservoirs in China have the characteristics of diversified accumulation pattern, complex structure and varying reservoir conditions. Concerning these characteristics, this article tracks the technical breakthroughs and related practices since the 1950 s, summarizes the developed theory and technologies of carbonate reservoir development, analyzes their adaptability and problems, and proposes their development trend. The following theory and technologies have come into being:(1) carbonate reservoir formation mechanisms and compound flow mechanisms in complex medium;(2) reservoir identification and description technologies based on geophysics and discrete fracture-vuggy modeling method;(3) well testing analysis technology and numerical simulation method of coupling free flow and porous media flow;(4) enhanced oil recovery techniques for nitrogen single well huff and puff, and water flooding development techniques with well pattern design in spatial structure, changed intensity water injection, water plugging and channel blocking as the core;(5) drilling and completion techniques, acid fracturing techniques and its production increasing techniques. To realize the efficient development of carbonate oil and gas reservoirs, researches in four aspects need to be done:(1) complex reservoir description technology with higher accuracy;(2) various enhanced oil recovery techniques;(3) improving the drilling method and acid fracturing method for ultra-deep carbonate reservoir and significantly cutting engineering cost;(4) strengthening the technological integration of information, big data, cloud computation, and artificial intelligence in oilfield development to realize the smart development of oilfield.

Simulation of gas production from hydrate reservoir by the combination of warm water flooding and depressurization

Gas production from hydrate reservoir by the combination of warm water flooding and depressurization is proposed,which can overcome the deficiency of single production method.Based on the combination production method,the physical and mathematical models are developed to simulate the hydrate dissociation.The mathematical model can be used to analyze the effects of the flow of multiphase fluid,the kinetic process of hydrate dissociation,the endothermic process of hydrate dissociation,ice-water phase equilibrium,the convection and conduction on the hydrate dissociation and gas and water production.The mechanism of gas production by the combination of warm water flooding and depressurization is revealed by the numerical simulation.The evolutions of such physical variables as pressure,temperature,saturations and gas and water rates are analyzed.Numerical results show that under certain conditions the combination method has the advantage of longer stable period of high gas rate than the single producing method.

Low resistivity oil(gas)-bearing reservoir conductive model——Dual water clay matrix conductive model in the north area of Tarim Basin, Xinjiang, China

Shaly sands reservoir is one of the most distributive types of the oil(gas)-bearing reservoirs discovered in China, and low resistivity oil(gas)-bearing reservoirs are mostly shaly sands reservoirs. Therefore, shaly sands reservoir conductive model is the key to evaluate low resistivity oil(gas)-bearing reservoirs using logging information. Some defects were found when we studied the clay distribution type conductive model, dual-water conductive model, conductive rock matrix model, etc. Some models could not distinguish the conductive path and nature of microporosity water and clay water and some models did not consider the clay distribution type and the mount of clay volume. So, we utilize the merits,overcome the defects of the above models, and put forward a new shaly sands conductive model-dual water clay matrix conductive model (DWCMCM) in which dual water is the free water and the microporosity water in shaly sands and the clay matrix(wet clay) is the clay grain containing water. DWCMCM is presented here, the advantages of which can tell the nature and conductive path from different water (microporosity water and freewater), in consid-eration of the clay distribution type and the mount of clay volume in shaly sands. So, the results of logging interpretation in the oil(gas)-bearing reservoirs in the north of Tarim Basin area, China with DWCMCM are better than those interpreted by the above models.

Capsule polymer flooding for enhanced oil recovery

To solve the problems of shear degradation and injection difficulties in conventional polymer flooding,the capsule polymer flooding for enhanced oil recovery(EOR)was proposed.The flow and oil displacement mechanisms of this technique were analyzed using multi-scale flow experiments and simulation technology.It is found that the capsule polymer flooding has the advantages of easy injection,shear resistance,controllable release in reservoir,and low adsorption retention,and it is highly capable of long-distance migration to enable viscosity increase in deep reservoirs.The higher degree of viscosity increase by capsule polymer,the stronger the ability to suppress viscous fingering,resulting in a more uniform polymer front and a larger swept range.The release performance of capsule polymer is mainly sensitive to temperature.Higher temperatures result in faster viscosity increase by capsule polymer solution.The salinity has little impact on the rate of viscosity increase.The capsule polymer flooding is suitable for high-water-cut reservoirs for which conventional polymer flooding techniques are less effective,offshore reservoirs by polymer flooding in largely spaced wells,and medium to low permeability reservoirs where conventional polymers cannot be injected efficiently.Capsule polymer flooding should be customized specifically,with the capsule particle size and release time to be determined depending on target reservoir conditions to achieve the best displacement effect.

Evaluation of sour gas-low salinity waterflooding in carbonate reservoirs-A numerical simulation approach

Although significant amount of H_(2)S(sour gas)rich natural gas is estimated globally,but not much attention has been given to the application of H_(2)S in the oil recovery process.Recent studies on the use of H_(2)S in oil recovery processes showed that H_(2)S has the potential of improving the oil recovery,and it can be even more effective than using CO_(2) in some processes.H_(2)S can equally dissolve in the water,react with the reservoir rock to change its surface charge,porosity,and permeability.However,previous in-vestigations on H_(2)S oil recovery attributed the improved oil recoveries to the higher miscibility of H_(2)S in the oil,and the reduction in the oil viscosity.Therefore,there is limited understanding on the H_(2)S-oil-brine-rock geochemical interactions,and how they impact the oil recovery process.This study aims to investigate the interactions between H_(2)S,oil,and carbonate formations,and to assess how the combi-nation of H_(2)S and low salinity water can impact the wettability and porosity of the reservoirs.A triple layer surface complexation model was used to understand the influence of key parameters(e.g.,pressure,brine salinity,and composition)on the H_(2)S-brine-oil-rock interactions.Moreover,the effects of mineral content of the carbonate rock on H_(2)S interactions were studied.Thereafter,the results of the H_(2)S-oil-brine-rock interactions were compared with a study where CO_(2) was used as the injected gas.Results of the study showed that the seawater and its diluted forms yielded identicalζ-potential values of about 3.31 mV at a pH of 3.24.This indicates that at very low pH condition,pH controls the ζ-potential of the oil-brine interface regardless of the brine's ionic strength.The study further demonstrated that the presence of other minerals in the carbonate rock greatly reduced the calcite dissolution.For instance,the calcite dissolution was reduced by 4.5%when anhydrite mineral was present in the carbonate rock.Findings from the simulation also indicated that CO_(2) produced negative ζ-potential values for the car-bonate rocks,and these values were reduced by 18.4%-20% when H_(2)S was used as the gas phase.This implies that the H_(2)S shifted the carbonate rockζ-potentials towards positive.The outcomes of this study can be applied when designing CO_(2) flooding and CO_(2) storage where the gas stream contains H_(2)S gas since H_(2)S greatly influences the dissolution of the carbonate mineral.

低渗透油藏压驱技术现状及发展趋势

压驱技术是近年来针对低渗透油藏高效开发而提出的一种增加储层动用程度、提高原油采收率的储层改造技术。压驱技术先通过高压小排量向地层注入大量携带化学剂的液体,然后进行焖井,通过压力的扩散和化学剂与裂缝孔隙中的原油充分置换而达到增产的目的。文中结合国内外压驱技术的最新研究动态,从压驱技术现状、设计原则、设计方法、应用分析及发展趋势等方面展开论述,重点分析了压驱技术与水力压裂技术的区别、增产机理和设计方法以及现场应用效果等,同时也指出了当前压驱技术理论研究方面的欠缺,展望了该技术的发展趋势和应用前景。

胜利油田稠油油藏开发技术进展

针对胜利油田不同类型稠油油藏的地质特点及开发矛盾,形成了一套较为完善的稠油油藏开发技术系列,并取得了显著的开发效果。从各项技术的理论基础和矿场应用2个方面,总结了不同类型稠油油藏开发技术进展。对于高轮次吞吐后的稠油油藏,基于非达西渗流理论,形成了井网加密技术;对于敏感性稠油油藏,形成了近热远防理论,降低了水敏对开发的不利影响;对于特超稠油油藏,通过HDCS技术的协同降黏、膨胀增能作用,解决了“注不进、采不出”的开发难题;对于低效水驱稠油油藏,通过转蒸汽驱,达到加密角井流线、水井流线逆向的目的,从而提高该类油藏的采收率;对于深层稠油油藏,以气热协同保热强热、热剂协同接替助驱、气剂协同均衡热前缘的协同增效作用机理认识为基础,形成了多元热复合驱油理论,实现了深层稠油的有效动用;对于薄层稠油油藏,通过热+水平井复合开发模式,提高了油藏的吸汽能力和动用范围;对于浅薄层超稠油油藏,通过HDNS技术增能降黏扩波及,实现了该类油藏的高效开发。胜利油田稠油油藏开发技术系列的应用,为胜利油田稠油效益开发、绿色开发提供了技术支撑。

大庆油田二类B油层聚驱剖面动用规律及其改善

大庆油田聚合物驱应用规模不断扩大,开发对象转向性质较差的二类B油层,现有聚合物与油层适应性不强,剖面动用规律不明确,不同地区聚驱开发效果差异较大。针对上述问题,应用矿场剖面数据统计和室内实验分析,研究了二类B油层剖面动用规律和剖面改善方法。结果表明:从吸水层动用情况来看,喇嘛甸地区由于发育厚层河道砂,油层物性好,油层有效厚度动用比例最高,油层以多次动用为主,突进层多,相对吸液量高;萨中和萨南地区河道砂发育规模小,薄砂层较多,物性差,有效厚度动用比例较低,但聚驱后,有效厚度动用比例相比水驱分别增大了12.5%和15.4%,渗透率为100~300 mD的储集层吸入剖面改善明显;从未吸水层动用来看,二类B油层纵向非均质性强,导致层间有效厚度未动用比例较高,剖面改善应以均衡层间动用为主;抗盐聚合物高、低质量浓度交替注入可延缓含水率上升时间,增加低渗透层吸液量,聚驱采出程度提高显著。在喇嘛甸北北块A区开展了DS1200抗盐聚合物和高、低质量浓度交替注入试验,降水增油效果好,可为大庆油田二类B油层聚驱剖面改善提供技术指导。

断控缝洞型油藏底水驱剩余油分布规律及挖潜策略

根据断控缝洞型油藏构造成因和地震资料,分析了典型缝洞结构特征,设计并制作了“树状”缝洞结构三维大尺度可视化物理模型,开展了不同生产速度、不同井储配置关系下底水驱和底水驱后多介质协同开采实验,揭示了该类缝洞结构下底水驱剩余油形成机制和分布规律,明确了底水驱后不同开采方式下剩余油动用特征。研究表明,“树状”缝洞结构中,底水驱后剩余油主要包括非井控区断裂带剩余油和井控区断裂带顶部“阁楼型”剩余油;高生产速度下存在明显的底水沿断裂带的水窜现象,采用间歇式排采可以有效削弱断裂带间的干扰效应,起到抑制水窜的效果;与直井开采相比,水平井能够降低断裂带间的导流能力差异,呈现出较好的抗水窜能力;水平井越靠近“树冠”上部,底水驱阶段采收率越高,但综合考虑底水驱及后续注气开发,水平井部署在“树冠”中部且钻穿较多数量的断裂带时总采收率更高;底水驱后顶部注气吞吐优于气驱、大段塞吞吐优于小段塞吞吐,既可以有效动用与油井横向连通的井控区断裂带顶部“阁楼型”剩余油又可以动用非井控区断裂带剩余油,从而大幅度提高采收率。