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.

A Review of Formation Mechanism Study on Reservoirs with Tilted Oil-water Contacts

The distribution characteristics of the oil-water contact are the basis for the reservoir exploration and development and reserves evaluation. The reservoir with a tilted oil-water contact has a unique formation mechanism, and the understanding of its distribution and formation mechanism will directly affect the evaluations for the reservoir type, well deployment, selection of well pattern and type, determination of test section, and reserves evaluation. Based on the analysis of reservoir characteristics, petrophysical properties and geological structure in 40 reservoirs worldwide with tilted oil-water contacts, the progress of the research on the formation mechanisms of titled oil-water contacts is summarized in terms of the hydrodynamic conditions, reservoir heterogeneity, neotectonic movement and oil-gas exploitation. According to the formation mechanism of tilted oil-water contacts and the needs of exploration research, different aspects of research methods are summarized and classified, such as the calculation of equipotential surfaces for oil and water in the formation, analysis of formation pressure and analysis of reservoir physical properties and so on. Based upon statistical analysis, it is suggested that the degree of the inclination of the oil-water contact be divided based on the dip of oil-water contact（DipTOWC）. The tilted oil-water contact is divided into three categories： large dip（DipTOWC≥55 m/km）, medium dip（4 m/km≤DipTOWC55 m/km）, and small dip（DipTOWC4 m/km）. The classification and evaluation method can be combined with structure amplitude and reservoir property. The formation mechanism of domestic and international reservoirs with tilted oil-water contacts are summarized in this paper, which have important significance in guiding the exploration and development of the oilfield with tilted oil-water contacts, reserves evaluation, and well deployment.

The control effect of low-amplitude structure on oil-gaswater enrichment and development performance of ultra-low permeability reservoirs

Based on drilling, logging, test production and dynamic monitoring data, the control effects of low-amplitude structure on hydrocarbon accumulation and development performance of ultra-low permeability reservoirs were discussed by using the methods of dense well pattern, multi-factor geological modeling, macro and micro analysis and static and dynamic analysis. The results show that the low-amplitude structure always had a significant control and influence on the distribution and accumulation of original hydrocarbon and water and the evolution trend of water flooding performance in ultra-low permeability reservoirs, and it was not only the direction of oil and gas migration, but also a favorable place for relative accumulation of oil and gas. The controlling effect of low-amplitude structure on ultra-low permeability reservoir mainly depended on its tectonic amplitude and scale;the larger the tectonic amplitude and scale, and the higher the tectonic position of the low amplitude structure, the better the reservoir characteristic parameters, oil and gas enrichment degree and development effect, and the larger the spatial scope it controlled and influenced;water cut and oil well output always fluctuated orderly with the height of the low-amplitude structure;the dynamic response of waterflooding was closely related to the relative structural position of the injection and production wells;the injected water always advanced to the low-lying area of the structure first and then moved up to the high-lying area of the structure gradually;with the continuous expansion of the flooded area, part of the oil and gas in the low-lying part of the structure was forced to be distributed to the high part of the structure, resulting in a new oil and gas enrichment, so that the dynamic reserves of oil wells in the high part increased, and the production capacity remained stable.

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 Oilfield Waters fromthe Turpan Depression, Xinjiang and Their Petroleum Geological Significance

This paper, based on the fundamental inorganic chemical and organic geochemical characteristics of oilfield waters from the Turpan Depression, presents the contents of organic matter, the distribution of low-carbon fatty acids and the contents of aromatic hydrocarbons as well as their principal ultraviolet absorption spectral and fluorescence spectral characteristics in oilfield waters from different oil/gas-bearing areas. The oil/gas reservoirs in this depression are classified in terms of their conserving conditions. In addition, the paper also discusses the chemical characteristics of oilfield waters from different types of oil/gas reservoirs with an emphasis on the characteristics of their localization in the γ_Na/γCa-γNa/γ_Cl correction diagram. On this basis it is attempted to expound the fundamental geochemical characteristics of oilfield waters from the Turpan Depression and their geological significance.

The impact of connate water saturation and salinity on oil recovery and CO2 storage capacity during carbonated water injection in carbonate rock

Carbonated water injection(CWI)is known as an efficient technique for both CO2 storage and enhanced oil recovery(EOR).During CWI process,CO2 moves from the water phase into the oil phase and results in oil swelling.This mechanism is considered as a reason for EOR.Viscous fingering leading to early breakthrough and leaving a large proportion of reservoir un-swept is known as an unfavorable phenomenon during flooding trials.Generally,instability at the interface due to disturbances in porous medium promotes viscous fingering phenomenon.Connate water makes viscous fingers longer and more irregular consisting of large number of tributaries leading to the ultimate oil recovery reduction.Therefore,higher in-situ water content can worsen this condition.Besides,this water can play as a barrier between oil and gas phases and adversely affect the gas diffusion,which results in EOR reduction.On the other hand,from gas storage point of view,it should be noted that CO2 solubility is not the same in the water and oil phases.In this study for a specified water salinity,the effects of different connate water saturations(Swc)on the ultimate oil recovery and CO2 storage capacity during secondary CWI are being presented using carbonate rock samples from one of Iranian carbonate oil reservoir.The results showed higher oil recovery and CO2 storage in the case of lower connate water saturation,as 14%reduction of Swc resulted in 20%and 16%higher oil recovery and CO2 storage capacity,respectively.

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.

Development of High Viscous Oil in Sandstone Reserviors During the High Water Cut Stage，Gudao Oilfield

The oi!bearing area of Gudao Oilfield covers 80.9 square kilometers.with 373 million tons of oil in place.It is a large drape anticlinal.Neogene Gu-dao Formation is main oil-beraing reservoir devel-oped with dip gentle from 30'to 1°30'in general.The main oil-bearing sequences can be divided into 6 sand groups and 34 layers in detail.in which the Ng°-Ng°sand groups are the main payzones in which oil in place accounts for 97.2%of the total.

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.

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。

鄂尔多斯盆地长6和长8段致密油储层驱渗特征研究

鄂尔多斯盆地致密油储量丰富,主要富集在延长组三叠系长6和长8油层组,是目前增储上产的重要目标。为了推动该类油藏的规模效益开发,以深化储层特征与渗流规律认识为目的,在前期研究基础上,引入核磁共振、高压压汞、纳米CT扫描和高精度流体计量等新技术,系统开展了致密油储层微观孔隙结构、原油赋存状态以及水驱与渗吸动用规律研究。研究成果表明,致密油储层发育多尺度孔隙,孔隙结构以小孔-细喉型为主且连通性较好。物理模拟研究表明,原油在致密油储层的各类孔隙中均有分布,但大、中孔隙中原油的含量远高于小孔隙中的原油含量,且多以游离态存在,流动性好,是油田开发的主要对象。水驱油实验表明,致密油储层虽然存在启动压力梯度,但当驱替压力大于启动压力之后能够建立有效驱替系统,且随着驱替压力的增大水驱油效率会有所提高。核磁共振技术与水驱油实验或渗吸实验相结合,清楚地表明了不论采用水驱方式还是渗吸方式开发,致密油储层优先动用的都是较大孔隙中赋存的原油,小孔隙中赋存的原油动用难度较大。这些研究成果为探索更加有效的开发技术提供了依据。

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。

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。

碳酸盐岩缝洞型油藏流固耦合下的油水两相流动特征

为提高缝洞型碳酸盐岩油藏采收率,探究其流固耦合下的油水两相流动特性,根据不同介质中的流体流动规律,建立了Stokes-Darcy两相流体流动模型;基于有效应力原理和广义胡克定律,建立了适用于缝洞型碳酸盐岩油藏的油水两相Stokes-Darcy流固耦合数学模型;分别针对有无流固耦合的缝洞型碳酸盐岩油藏,进行了宏观和细观的油水两相流体流动模拟。研究结果表明:油藏有无流固耦合作用,其油水两相流体流动特性在基质区差异较大,在溶洞内差异较小,注水速度对缝洞型碳酸盐岩油藏的油水流动影响较大。

断溶体油藏追踪油水界面变化的新方法

在底水驱动型断溶体油藏中确定原始油水界面及追踪动态油水界面变化一直是制约剩余油预测的重要难题。此文聚焦油水界面的油藏本质,精细量化了储集体的孔隙体积,开发动态数据试井化处理计算水油体积比,动静结合等比例分配油水体积计算出原始油水界面。在油藏内部划分出油水界面,后期根据水驱动用过程评估曲线划分水驱阶段,追踪动态油水界面变化,避免陷入前期常规方法选取参数困难、计算误差大的困境。开发实践证实该方法得到的结果误差小,计算方便快捷,具有推广应用前景。

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。

致密油藏驱渗结合采油可行性研究

致密油藏孔喉较小而渗吸作用显著,为提高致密油藏水驱效率,提出驱渗结合采油方法,同时利用驱替与渗吸作用。为验证该方法的可行性与主控因素,在水驱模型的基础上,考虑了渗吸作用,并基于实验数据特征建立了渗吸项模型,建立了驱渗结合采油数值模拟模型。结果表明,渗吸作用有效增加了注入水的波及面积,有效置换出基质中的原油,提升了采油效率;主控地质因素包括基质/裂缝孔隙度、渗透率和渗吸经验参数,主控工程因素包括注水压力、裂缝间距和半长;现场应用表明相较水驱方式,驱渗结合采油的日产油速度提高了约1倍,受效时间约为200 d,提高累产约为340 t,说明驱渗结合采油工艺可有效提高中国致密油藏的采收率,所建模型可用于驱渗结合采油的优化设计。

断块油藏高含水井关井后剩余油再动用运移规律微观模拟

基于微观可视化光刻玻璃模型,从微观角度定性、定量研究了断块油藏高含水井关井后剩余油再动用运移规律,并开展了影响因素分析。结果表明:水驱后关井期间剩余油再动用类型主要为滴状、柱状和簇状。关井期间剩余油会沿模型倾斜方向向高部位运移聚集,有利于后续水驱阶段进一步提高驱油效率。地层倾角的增大、原油黏度的减小有利于剩余油再动用;关井时间的增加有利于剩余油向高部位采出端接近聚集;后续水驱阶段注入速度的增大会增加波及面积。

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。

表面活性剂提高致密油藏注水吞吐效果的机理

注水吞吐作为致密油藏开采的一种经济、有效方法,已成功应用于各大油田。表面活性剂可提高致密油采收率,其作用机理尚需深化研究。研究将吞吐过程分为渗吸采油和反向驱替采油阶段,阐述表面活性剂对其作用规律。结果表明,在渗吸采油阶段,表面活性剂降低了渗吸采收率,但减小了原油从岩石表面剥离难度。在反向驱替采油阶段,表面活性剂可有效提高驱替采收率,同时大幅降低驱替压力。两性表面活性剂表现最佳,在清水的基础上提高采收率约5.00%,降低驱替压力7.00 MPa。其主要机理为降低界面张力、改变润湿性,减小原油从岩石表面剥离难度;减小毛管力和贾敏效应阻力,降低驱替压力。结果为表面活性剂在致密油藏注水吞吐的现场应用提供了理论依据。