Effect of high-multiple water injection on rock pore structure and oil displacement efficiency

Experimental methods,including mercury pressure,nuclear magnetic resonance(NMR)and core(wateroil)displacement,are used to examine the effects of high-multiple water injection(i.e.water injection with high injected pore volume)on rock properties,pore structure and oil displacement efficiency of an oilfield in the western South China Sea.The results show an increase in the permeability of rocks along with particle migration,an increase in the pore volume and the average pore throat radius,and enhanced heterogeneity after high-multiple water injection.Compared with normal water injection methods,a high-multiple water injection is more effective in improving the oil displacement efficiency.The degree of recovery increases faster in the early stage due to the expansion of the swept area,and the transition from oil-wet to water-wet.The degree of recovery increases less in the late stage due to various factors,including the enhancement of heterogeneity in the rocks.Considering both the economic aspect and the production limit of water flooding,it is recommended to adopt other technologies to further enhance oil recovery after 300 PV water injection.

Comparison of oil displacement mechanisms and performances between continuous and dispersed phase flooding agents

To compare the oil displacement mechanisms and performances of continuous phase flooding agent(traditional polymer solution) and dispersed phase flooding agent(particle-type polymer SMG dispersion), the particle phase separation of SMG dispersion migrating in pores was simulated by using the microfluidic technology. Theoretically guided by the tree fork concentration distribution of red cells in biological fluid mechanics, the concentration distribution mathematical model of SMG in different pores is established. Furthermore, the micro and macro physical simulation experiments of continuous and dispersed phase flooding agents were carried out. The results show that the continuous flooding agent enters all the swept zones and increases the flow resistance in both larger and small pores. On the contrary, the particle phase separation phenomenon occurs during the injection process of dispersed flooding agent. The SMG particles gather in the larger pore to form bridge blinding, and the carrier fluid displace oil in the small pore. Working in cooperation, the SMG particle and carrier fluid drive the residual oil in the low permeability layers step by step and achieve the goal of enhanced oil recovery. The laboratory experimental results indicate that, the oil increment and water reduction effect of dispersed flooding agent is much better than that of continuous flooding agent, which is consistent with the field test results.

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.

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.

Geochemical characteristics of oils among real cores in displacement model

Physical simulation experiment on oil displacement is an important approach to understand the mechanism and efficiency of displacement. Physical simulation experiments on water-flooding and chemical flood-ing in real cores with different lithologies and physical properties, reservoir Rock-Eval, TLC-FID, GC of saturated hydrocarbon fractions and GC-MS of saturated and aromatic hydrocarbon fractions were performed to investigate differences in the geochemistry of residual oils in the cores processed by water-flooding and chemical flooding. After fine sandstone was displaced with the two methods, the preferable replacement efficiency was displayed by the chemical constitutions of residual oils. As to glutenite, water-flooding is less effective, while chemical flooding has excellent performance according to changes in chemical compounds in oils. The results showed that the geochemical characteristics of the reservoir oils and lithology and physical properties of reservoir bed need to be considered in selecting replacement methods. In addition, the geochemical parameters for residual oils slightly changed during water-flooding and chemical flooding, which suggested the water-flooding and chemical flooding could not affect the application of these parameters in geochemistry.

Mechanism of expanding swept volume by nano-sized oil-displacement agent

The effect of expanding swept volume by iNanoW1.0 nanoparticles in ultra-low permeability core was studied by low-field nuclear magnetic resonance(LF-NMR)technology,and the mechanism of expanding swept volume was explained by oxygen spectrum nuclear magnetic resonance(17O-NMR)experiments and capillarity analysis.The results of the LF-NMR experiment show that the nano-sized oil-displacement agent iNanoW1.0 could increase the swept volume by 10%-20%on the basis of conventional water flooding,making water molecules get into the low permeable region with small pores that conventional water flooding could not reach.17O-NMR technique and capillary analysis proved that iNanoW1.0 nanoparticles could weaken the association of hydrogen bonds between water molecules,effectively change the structure of water molecular clusters,and thus increasing the swept volume in the low permeable region.The ability of weakening association of hydrogen bonds between water molecules of iNanoW1.0 nanoparticles increases with its mass fraction and tends to be stable after the mass fraction of 0.1%.

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.

表面活性剂对水驱普通稠油油藏的乳化驱油机理

为了研究乳化降黏驱油剂对不同渗透率的水驱普通稠油油藏的驱油效率和孔隙尺度增效机理,选取了烷基酚聚氧乙烯醚(J1)、α-烯基磺酸盐类表面活性剂(J2)、十二烷基羟磺基甜菜碱(J3)、J3与烷基酚聚氧乙烯醚羧酸盐复配表面活性剂(J4)作为驱油剂,开展了4种驱油剂一维驱油和微观驱油模拟实验,明确了乳化降黏驱油剂在孔隙尺度的致效机理。结果表明,降低界面张力对提高驱油效率的作用大于提高乳化降黏率。在油藏条件下,乳化降黏驱油剂需要依靠乳化降黏和降低界面张力的协同增效作用,才能大幅提高驱油效率。乳化降黏驱油剂的乳化能力越强、油水界面张力越低,驱油效率增幅越大。当化学剂乳化降黏率达到95%时,油水界面张力从10^(-1)mN/m每降低1个数量级,化学剂在高渗透和低渗透岩心中的驱油效率依次提高约10.0%和7.8%。乳化降黏驱油剂注入初期通过降低界面张力,使得高渗透岩心和低渗透岩心中的驱替压力分别为水驱注入压力的1/2和1/3,从而提高注入能力。注入后期大块的原油被乳化形成大量不同尺寸的油滴,增强原油流动性,提高驱油效率。乳化形成的界面相对稳定的稠油油滴,能暂堵岩石的喉道和大块稠油与岩石颗粒形成的通道。油滴的暂堵叠加效应,使高渗透和低渗透岩心的驱替压差分别为水驱压差的5.2倍和32.3倍,大幅提高了注入压力,从而扩大平面波及面积。降黏驱油剂驱油实现了提高驱油效率的同时扩大波及范围。研究结果为水驱稠油开发用驱油剂的研发提供参考,为大幅提高水驱普通稠油采收率奠定基础。

胜利油田水驱开发技术进展及发展方向

水驱油藏是中国东部老油田开发的主体,经过长期注水开发已整体进入特高含水期,室内研究及矿场实践表明,仍有大幅度提高采收率的潜力,但受储层非均质性和开发动态非均质性影响,科学开发和效益开发难度加大,亟需攻关进一步提高采收率技术。整装油藏针对特高含水后期极端耗水严重、效益稳产及水驱提高采收率难等问题,深化了极端耗水层带理论,创新形成了层系近阻重组开发技术、特高含水油藏矢量开发技术和特高含水后期流场调整开发技术,实现了控耗水、降递减,平均采收率为43.7%;断块油藏针对断层多、断块小的特点及特高含水期剩余油规模小、动用难的问题,深化剩余油富集规律及水动力调控机制认识,创新形成了人工边水驱、立体开发等主导开发技术系列,提高了储量控制和水驱动用程度,平均采收率为29.4%,支撑了断块油藏效益稳产;低渗透油藏针对储层物性差、有效建驱难等问题,持续开展非线性渗流机理和压驱开发机理研究,攻关配套开发技术,不断拓宽开发界限,创新形成特低渗透油藏仿水平井注水、一般低渗透油藏井网适配提高采收率、低渗透-致密油藏压驱注水等差异开发技术系列,平均采收率为15.7%,实现了低渗透油藏提速提效开发。通过以上技术进步,实现了特高含水期水驱油藏的效益开发。结合不同类型油藏开发特点及面临形势,对水驱油藏进一步提高采收率提出了下步发展方向。

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。

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。

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。

普通稠油非均相复合体系组分驱油贡献率

非均相复合体系能实现协同调驱,在稠油开发方面极具潜力,但各组分驱油贡献率不明确,给体系优化与选择带来盲目性。针对由部分水解聚丙烯酰胺、双效型表面活性剂和预交联凝胶颗粒(B-PPG)组成的非均相复合体系,在分析其界面与封堵性能和驱油特征的基础上,开展了聚合物、二元复合体系和非均相复合体系驱油实验;依据3类体系驱油的采收率增幅,归一化计算了不同水油黏度比下非均相复合体系组分驱油贡献率。结果表明,0.106~0.150 mm(150~100目)B-PPG膨胀后的粒径中值为800μm。该非均相复合体系与渗透率为1.1μm~2的填砂模型匹配,运移封堵阻力系数与残余阻力系数分别为420.5和203.0,更低渗透率(0.30μm~2)的填砂模型则难以进入。对于渗透率级差约为3.0的并联填砂模型,非均相复合体系具有较强的调驱能力,最高注入压力为0.42 MPa、低渗透模型分流率最高达到42.2%;而二元复合体系的最高注入压力仅为0.25 MPa、低渗透模型分流率仅为24.3%。当水油黏度比为0.05~0.46时,非均相复合体系中聚合物驱油贡献率(43.1%~84.1%)最高,表面活性剂(22.1%~7.6%)最低,B-PPG(34.8%~8.3%)介于两者之间。水油黏度比(≥0.46)较高时,表面活性剂和B-PPG驱油贡献率较小,聚合物或二元复合驱后非均相复合驱增油潜力有限;水油黏度比(≤0.2)较低时,表面活性剂和B-PPG驱油贡献率大,水驱或聚合物、二元复合驱后非均相复合驱增油潜力较大。

一种适用于油基钻井液堵漏水泥浆体系研发

水泥浆堵漏是解决恶性漏失的有效措施之一,但是水泥浆在油基钻井液中难以凝结固化,致使其使用受限。从油基钻井液污染水泥浆机理出发,开发油水置换剂,并对胶凝体系和配套降失水剂和缓凝剂进行研选,开发油基钻井液堵漏水泥浆体系,并对水泥浆体系性能进行评价。研究表明:通过微乳液共聚法(即油相和水相同时引发聚合)制备了油水置换剂,在油井水泥中加入油水置换剂后,钻井液与水泥浆的相容性良好,水泥浆与油基钻井液体积比为50∶50的混浆体系在50℃条件下养护时间24 h,强度可达2 MPa左右,且油水置换剂具有很好的广谱性能,现场不同区域取的不同类型的油基钻井液,均发展强度;研选了配套降失水剂BXF-200LL和缓凝剂GH-9,开发出了适用于油基钻井液堵漏的水泥浆体系,油水置换剂对水泥浆稠化没有不良影响,且抗温达120℃。

枯竭油藏型储气库库容量化室内实验研究

在油藏改建地下储气库时,为了研究不同初始含水饱和度对库容的影响,利用实际矿场岩心开展了不同初始含水饱和度条件下气驱油水多轮次注采实验,分析了不同初始含水饱和度下气驱油水后的驱替效率及建库效果。结果表明,低含水饱和度条件下,油相的相对渗透率显著高于水相而更易被驱替出,因此主要通过气驱油来提高储气空间;中、高含水饱和度时,水相更易被驱替出,储气空间的提高逐渐由被驱替出的原油体积贡献转向于由驱替出的水相体积贡献。相同注采轮次下,由于储层岩石水湿及渗吸作用,高初始含水饱和度时的剩余水饱和度增大,气驱油水总的驱替效率降低,储气库的注采能力和库容相对减小;储层初始含水饱和度增大会降低气驱油水的驱替效率,不利于提高原油采收率及储气库扩容;初始含水饱和度越高,储气库达容时间越久,建库初期的注采能力越低。该研究成果可为油藏型储气库注采能力评价和库容分析提供指导。

水气交替提高采收率技术进展

水气交替(WAG)注入技术是一种提高油藏采收率的有效方法,已经在多种类型的油藏中得到应用。本文介绍了WAG技术的发展背景和研究意义,然后根据注入方式、流体类型和混相状态对WAG技术进行了分类,并分别阐述了各类WAG技术的优缺点和驱油机制;分析水的矿化度、滞后效应、油藏非均质性、润湿性和WAG比例等因素对WAG技术效果的影响。基于WAG技术在实施过程中遇到的气体提前突破、设备问题和沥青质沉积等挑战,提出相应的解决措施,对未来的研究方向进行展望。

三叠系油藏堵驱结合技术的探索应用

针对胡尖山油田三叠系油藏储层非均质性强、注入水波及范围小、驱替效率低且多轮次调剖调驱效果减弱等问题,以H4区油藏为研究对象,基于前期矿场试验效果,优选近井调剖封堵体系与纳米微球深部调驱体系相结合,充分发挥协同治理优势。结果表明,堵驱结合技术在非均质油藏中具有较好的控水增油适应性,对应油井见效率、含水率下降幅度、平均单井增油量均优于单一体系,为同类型油藏调剖调驱体系组合优化提供借鉴参考。

海上油田一种水基深部调驱剂的研究与应用

为达到高含水率油田深部调驱的目的,对水基超分子微球进行粒径分布、缔和性能等评价,发现该微球粒径分布在纳米-微米级别,盐水条件下缔和现象聚集体粒径扩大倍数可达5倍以上,静态条件下体系浓度在1000 mg/L以上时可实现颗粒有效聚集。岩心驱替模拟实验条件下,体系注入过程中阻力系数低,高含水率条件以及存在渗透率级差条件下依然具有较高的提高采收率幅度。该体系适用性良好,对“双特高”油田调驱提高深部处理能力具有一定借鉴意义。

中渗透油藏化学驱开发效果影响因素研究

针对中国石化中渗透油藏化学驱开发效果主要影响因素不明确的问题,选取典型中渗透区块,采用数值模拟手段,以驱油效果和经济指标为目标,开展了油藏地质参数、开发动态参数及驱油体系参数对化学驱开发效果的影响规律研究,并结合中国石化化学驱现场应用情况,给出了中渗透油藏实施化学驱的相关参数建议。建议优先实施块状油藏化学驱,储量规模150×10^(4)t左右、井组采注井数比介于1.5~2.5之间实施化学驱能取得较好效果;在油藏进入高含水阶段需尽早实施化学驱,注入含水时机越早(含水低于90%)、剩余油饱和度越高(剩余油饱和度高于30%),则化学驱效果越好;驱油体系的注入总量、注入方式、注入段塞PV及注入浓度等决定了化学驱的经济有效性,二元复合驱效果要好于聚合物驱,且注入总量控制在1200 PV•mg/L以内,注入方式以小段塞高浓度高频为主,注入段塞PV数控制在0.5~0.6 PV为宜。