Using cyclic alternating water injection to enhance oil recovery for carbonate reservoirs developed by linear horizontal well pattern

In view of high water cut and low oil recovery caused by the unidirectional flow in linear pattern of horizontal wells for the carbonate reservoirs in the Middle East,this paper provides a novel approach to improve oil recovery by converting linear water injection to cyclic alternating water injection patterns including cyclic alternating water injection with apparent inverted seven-spot pattern or apparent five-spot pattern and cyclic differential alternating water injection.The main advantage of using this strategy is that the swept efficiency is improved by changing injection-production streamlines and displacement directions,which means displacement from two different direction for the same region during a complete cycle.This technology is effective in increasing the swept efficiency and tapping the remaining oil,thus resulting in higher oil recovery.Field application with three new patterns in a carbonate reservoir in the Middle East is successful.By optimizing injection and production parameters based on the cyclic alternating well pattern,the test well group had a maximum increase of daily oil production per well of 23.84 m^(3) and maximum water cut drop of 18%.By further optimizing the distance(keep a long distance)between the heels of injection and production wells,the waterflooding performance could be better with water cut decreasing and oil production increasing.

Research into polymer injection timing for Bohai heavy oil reservoirs

Polymer flooding has been proven to effectively improve oil recovery in the Bohai Oil Field. However, due to high oil viscosity and significant formation heterogeneity, it is necessary to further improve the displacement effectiveness of polymer flooding in heavy oil reservoirs in the service life of offshore platforms. In this paper, the effects of the water/oil mobility ratio in heavy oil reservoirs and the dimensionless oil productivity index on polymer flooding effectiveness were studied utilizing rel- ative permeability curves. The results showed that when the water saturation was less than the value, where the water/oil mobility ratio was equal to 1, polymer flooding could effectively control the increase of fractional water flow, which meant that the upper limit of water/oil ratio suitable for polymer flooding should be the value when the water/oil mobility ratio was equal to 1. Mean while, by injecting a certain volume of water to create water channels in the reservoir, the polymer flooding would be the most effective in improving sweep efficiency, and lower the fractional flow of water to the value corresponding to △Jmax. Considering the service life of the platform and the polymer mobility control capacity, the best polymer injection timing for heavy oil reservoirs was optimized. It has been tested for reservoirs with crude oil viscosity of 123 and 70 mPa s, the optimum polymer flooding effec- tiveness could be obtained when the polymer floods were initiated at the time when the fractional flow of water were 10 % and 25 %, respectively. The injection timing range for polymer flooding was also theoretically analyzed for the Bohai Oil Field utilizing which provided methods for effectiveness. relative permeability curves, improving polymer flooding

Heating of heavy oil by circulating hot water in closed double casing in ultra-deep wells

In heavy oil production,the loss of energy to ambient surroundings decreases the temperature of the heavy oil flowing upwards in a vertical wellbore,which increases the oil viscosity and the oil may not flow normally in the wellbore.Therefore,it is necessary to lower the heavy oil viscosity by heating methods to allow it to be lifted easily.Heating of heavy oil in an oil well is achieved by circulating hot water in annuli in the well（tubing-casing annulus,casing-casing annulus）.In this paper,based on heat transfer principles and fluid flow theory,a model is developed for produced fluids and hot water flowing in a vertical wellbore.The temperature and pressure of produced fluids and hot water in the wellbore are calculated and the effect of hot water on heavy oil temperature is analyzed.Calculated results show that the hot water circulating in the annuli may effectively heat the heavy oil in the tubing,so as to significantly reduce both oil viscosity and resistance to oil flow.

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.

Water-cut rising mechanism and optimized water injection technology for deepwater turbidite sandstone oilfield: A case study of AKPO Oilfield in Niger Delta Basin, West Africa

Through the analysis of the reservoir connection relationship and the water-cut rising rules after water breakthrough in the highly volatile oil AKPO oilfield, a new model of water-cut rising was established, and the timing and strategy of water injection were put forward. The water-cut rising shapes of producers after water breakthrough can be divided into three types, and their water-cut rising mechanism is mainly controlled by reservoir connectivity. For the producers which directly connect with injectors in the single-phase sand body of the single-phase channel or lobe with good reservoir connectivity, the water-cut rising curve is "sub-convex". For the producers which connect with injectors through sand bodies developed in multi-phases with good inner sand connectivity but poorer physical property and connectivity at the overlapping parts of sands, the response to water injection is slow and the water-cut rising curve is "sub-concave". For the producers which connect with injectors through multi-phase sand bodies with reservoir physical properties, connectivity in between the former two and characteristics of both direct connection and overlapping connection, the response to water injection is slightly slower and the water-cut rising curve is "sub-S". Based on ratio relationship of oil and water relative permeability, a new model of water cut rising was established. Through the fitting analysis of actual production data, the optimal timing and corresponding technology for water injection after water breakthrough were put forward. Composite channel and lobe reservoirs can adopt water injection strategies concentrating on improving the vertical sweep efficiency and areal sweep efficiency respectively. This technology has worked well in the AKPO oilfield and can guide the development of similar oilfields.

Simulation and Modelling of Water Injection for Reservoir Pressure Maintenance

Water injection has shown to be one of the most successful,efficient,and cost-effective reservoir management strategies.By re-injecting treated and filtered water into reservoirs,this approach can help maintain reservoir pressure,increase hydrocarbon output,and reduce the environmental effect.The goal of this project is to create a water injection model utilizing Eclipse reservoir simulation software to better understand water injection methods for reservoir pressure maintenance.A basic reservoir model is utilized in this investigation.For simulation designs,the reservoir length,breadth,and thickness may be changed to different levels.The water-oil contact was discovered at 7000 feet,and the reservoir pressure was recorded at 3000 pounds per square inch at a depth of 6900 feet.The aquifer chosen was of the Fetkovich type and was linked to the reservoir in the j+direction.The porosity was estimated to be varied,ranging from 9%to 16%.The residual oil saturation was set to 25%and the irreducible water saturation was set at 20%.The vertical permeability was set at 50 md as a constant.Pressure Volume Temperature(PVT)data was used to estimate the gas and water characteristics.

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.

Development Plan of East Unity Oil Field, Sudan, Using Reservoir Simulation Study

Simulation study was applied in the development planning of East Unity oilfield, Sudan. A grid consisting of 2 000 cells was constructed. A major challenge of the study wasto evolve a full field development and future reservoir management strategy that would ensuremaximum recovery of oil based on well Un51. Simulation shows that Un51 as injection well inAradiebaC would yield better oil recovery than to be production well.

The Calculation of Heating Radius and Determination of Parameters in Heavy Oil Steam Stimulation

在稠油吞吐过程中,加热半径是热采中的重要指标,对注汽参数和生产制度起到了指导性作用。运用能量守恒原理,从热量注入方面考虑了蒸汽相变释放的气化潜热,从热量损失方面考虑井筒热量损失和顶底盖层热量损失,最终得到了新的加热半径计算公式。计算结果表明,加热半径受注汽参数、焖井时间、储层参数等因素影响,并系统阐述了岩层各物性参数的计算及选择方法。最后通过实例验证了该方法的计算值和试井解释出的值较为相符,为现场实际应用提供了可靠的方法。

Numerical simulation investigations of the applicability of THAI in situ combustion process in heavy oil reservoirs underlain by bottom water

The presence of a bottom water(BW)layer in heavy oil reservoirs can present substantial problems for efficient oil recovery for all recovery techniques.Hence,it is necessary to know how particular production processes are affected by different BW layer thicknesses,and how standard production procedures can be adapted to handle such reservoirs.Toe-to-heel air injection(THAI)is a thermally efficient process,generating in situ energy in the reservoir by burning a fraction of the oil-in-place as coke and has the potential to economically and environmentally friendly work in reservoirs with BW layer.However,to ascertain that,studies are needed first.These are conducted via numerical simulations using commercial reservoir thermal simulator,CMG STARS.This work has shown that the shape of the combustion zone in THAI remains forward-leaning even in the presence of a BW layer,indicating that the process is stable,and that there is no oxygen bypassing of the combustion front.However,the oil recovery rate is highly negatively affected by how large the thickness of the BWzone is,and the severity of such effect is determined to be proportional to the thickness of the BW layer.This study also shows that there is a period of low oil production rate which corresponds to mobilised oil displacement into the BW zone which in turn causes a surge in water production rate.The practical implication of this is that prolonged period of low oil production rates will expose companies and/or investors to higher risk due to the oil market volatility.In this study,it is also revealed that the height of the mobilised oil that is displaced into the BW zone equates to that of the displaced and replaced water thereby implying that when the BW layer thickness is 50%that of the oil layer(OL),less than 50%of the mobilised oil will be recovered when the entire reservoir is swept by the combustion front.Therefore,conclusively,applying the THAI process in its conventional form in reservoirs containing bottom water is not recommended,and as a result,a new strategy is needed to enhance process economics by improving the oil production and hence recovery rates.

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。

气水两相下降流中泡状流与段塞流转换边界研究

针对塔河油田气水混注驱替“阁楼油”过程中泡状流与段塞流转换边界不清的问题,利用数值模拟方法对气水两相下降流中泡状流与段塞流进行了模拟分析。结果表明:在气相表观流速为0.01~1.00 m/s、液相表观流速为0.03~2.00 m/s、管径为76 mm的模拟条件下,管道中主要为泡状流和段塞流;与模拟结果相比,Barnea、Kokal、薛玉卿模型预测的转换边界偏小,Bhagwat和Yijun模型预测的转换边界偏大;随着气相表观流速增加,泡状流向段塞流转换时所需液量逐渐增大;在低液量条件下,越靠近管道中心,气泡数量越多,空隙率越大;随液量增加,单个小气泡体积减小,气泡在整个管道横截面上分布越均匀。基于漂移模型,考虑气泡群滑脱速度,建立了新的泡状流与段塞流转换边界模型,216组文献数据验证结果显示,新模型准确率为95.37%,准确度较高。建立的泡状流—段塞流转换边界模型,不仅可提高井筒压力、温度模型的计算精度,同时对塔河油田现场注入井井口参数优化、注入设备优选和提高“阁楼油”驱替效率有很好的理论指导意义。

A Simulation Approach for Screening of EOR Scenarios in Naturally Fractured Reservoirs

Undoubtedly, plenty of hydrocarbon sources are located in carbonate rocks, particularly those which are naturally fractured that is still needed to study their characterization, because of their complex and unconventional behavior. Therefore, applying any processes that cause Enhancing Oil Recovery (EOR) from Naturally Fractured Reservoirs (NFR) seems necessary and useful. However, selecting the best developed scenario is always challenging. Screening criteria would determine the possibility of implementing an EOR process. While, utilizing trade marketing simulators can solve this problem. Moreover, simulation can evaluate other parameters such as water cut and gas-oil ratio. In this research, an aquifer-supported Iranian NFR with two parts that are separated to each other with a shale layer is considered in order to select the best EOR scenario. The fluid model is created using PVTi software. Various production scenarios included natural depletion, water flooding, miscible carbon dioxide injection, water-alternating-gas (WAG) injection, simultaneous water- alternating-gas (SWAG) injection, hybrid injection, and gas recycling are simulated in ECLIPSE Compositional (E300) and their recovery factor recorded as the target parameter. The developed scenarios are designed in a way that gives the optimized results, i.e. higher recovery factor, less water cut as well as the less gas-oil ratio. As a result, SWAG shows better conditions and is recommended for the further studies of the reservoir management plan in the future. Also, the role of the aquifer in the SWAG scenario is positive by creating a natural WAG in addition to the SWAG. Additionally, the average reservoir pressure through fractures reduces less in the SWAG than the other Scenarios, the oil and gas production rate reduce less in the SWAG and SWAG/ miscible gas respectively than the other scenarios. The maximum and the minimum water cut are related to the water flooding and SWAG, respectively.Finally, the simulation approach of EOR screening in NFR is better than other approaches, from the perspective of economic issues as well as the simplicity of the methods.

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。

浅层水平缝油藏底部注水研究

延长东部油田主力油层平均中深670 m、平均渗透率0.3~0.5 mD,为特超低渗浅层油藏,油井压裂时易形成水平裂缝,致使注水开发过程中油井出现快速水淹,造成油井产量大幅下降,采收率低。针对这一问题,在对水平缝注水渗流特征、压裂水平缝油井水淹规律和底部注水机理研究的基础上,提出了底部注水开发方式,并应用渗透率变异系数、突进系数、级差3个参数综合表征水窜层位与非水窜层位特征,为底部注水选层提供依据;通过室内核磁共振在线测试及岩心流动驱替实验,结合油藏数值模拟和现场示踪剂测试等综合手段,对注水参数进行了优化。开展底部注水先导性试验的3个井组单井产油量由0.054 t/ d提高到0.179 t/ d,含水率由15%下降到10%,地层压力提高了0.18 MPa,预测最终采收率提高了2.1个百分点,取得了较好效果。研究表明,当渗透率变异系数<0.5、突进系数<1.5、渗透率级差<5,注入速度为0.06 mL/ min,注水压力7 MPa时,注水开发效果最好。底部注水能够有效解决浅层水平缝油藏注水开发效果不佳的问题,为同类油藏的高效注水开发提供了参考。

致密油藏大排量注水吞吐技术及参数优化研究

针对致密油藏水平井自然渗吸采收率低和长期衰竭开发后期地层能量如何补充的难题,在储层基本特征、致密油藏注水吞吐采油机理的基础上,提出了大排量水平井注水吞吐。以鄂尔多斯盆地长7段致密油藏为研究对象,选取天然岩心和人造岩心相结合方式,利用核磁共振等方法,通过室内注水吞吐实验研究了自然渗吸和不同注水速度下吞吐动态渗吸的作用范围和微观孔隙动用特征,分析了排量对孔隙动用情况的影响,并开展了焖井时间影响实验,最后利用数值模拟方法对压裂水平井注水吞吐开发的注水量、焖井时间参数进行优化。研究表明:小排量时,注水吞吐主要动用的是大孔隙,中小孔隙动用较低;大排量时,注水吞吐不仅动用了大孔隙,且中小孔隙动用明显提高,使得整体的采收率出现较大增加。随着焖井时间的延长,油水置换作用越充分,使得注水吞吐采出程度越高,但其提高的程度逐渐稳定。对A9井进行数值模拟优化,得到最佳日注水量为900 m^(3),最佳焖井时间为24 d,在矿场试验取得成功,初期日增油2.11 t,有效期365 d,累计增油770 t。

准噶尔盆地东部北10井区中深层稠油CO_(2)非混相驱油技术

准噶尔盆地东部北10井区头屯河组油藏具有埋藏深、原油黏度大、储层强水敏的特点,自探明以来一直未获得有效动用。为了解决油藏难动用的难题进行了CO_(2)-稠油实验,在实验结果的基础上,根据试验区生产现状提出“非混相驱+吞吐”措施,利用数值模拟手段优化生产参数得到最优方案并预测出生产指标。结果表明:地层稠油注入CO_(2)后原油体积膨胀和黏度降低的能力大幅增强,是提高采收率的主要机理;井区稠油CO_(2)驱替方式为非混相驱,驱替过程中CO_(2)先以溶解和扩散作用为主,待建立驱替通道后才开始产出原油,采收率为29.60%;试验区非混相驱初期见效慢,为加快受效提出“油井吞吐”措施,数值模拟预测非混相驱配合3轮油井吞吐生产,最终采收率可达21.0%,解决了研究区油藏难动用的难题。研究成果对中深层强水敏稠油油藏的动用具有一定的借鉴意义。

海上低渗油藏CO_(2)混相驱可行性实验研究

海上珠江口盆地陆丰凹陷低渗、特低渗储量丰富,水驱开发难度大,注气开发需求迫切。CO_(2)驱是提高采收率的主要技术之一,但目前海上CO_(2)综合利用方面应用较少。以陆丰凹陷L油藏为例,开展了目标油藏原油注CO_(2)驱油机理实验和长岩心CO_(2)驱油效果评价实验,重点对比CO_(2)注入前后原油相态特征的变化,并对不同开发方式驱油效果进行了对比优化研究,为目标油田CO_(2)驱可行性提供依据。实验结果表明,CO_(2)可以有效提高低渗油藏的开发效果,提高采收率幅度可以在水驱的基础上提高11.75%,交替驱可以作为后期注CO_(2)防窜和进一步提高采收率的技术手段。实验研究结果对海上低渗油藏CO_(2)注气开发提供技术支持。

中国海油海上油田采油工程技术进展与展望

针对海上油田面临的油气开采技术难度大、重大技术迭代慢、大型作业技术应用成本高等多方面的挑战,中国海油经过数十年的发展,从稳产上产、技术迭代和降本增效等3方面推动技术变革,逐步形成了以“两提一降”为主线的数智化精细注水和稳油控水、大井距高强度稠油热采、低渗储层改造等三大工程技术,以及机采井延寿降耗、低产低效井增产、大修井作业、提高采收率等四类技术。提出了采油工程技术发展的10条技术路线,加快构建海上低成本采油工程技术体系,为推进中国海上油田采油工程技术高质量发展提供支撑。