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.

Quantitative Description of the Effects of Sweep Efficiency and Displacement Efficiency during Chemical Flooding on a Heterogeneous Reservoir

The processes of flooding—water flooding, polymer flooding and ternary combination flooding—were simulated respectively on a 2-D positive rhythm profile geological model by using the ASP numerical modeling software developed by RIPED (Yuan, et al. 1995). The recovery coefficient, remaining oil saturation, sweep efficiency and displacement efficiency were calculated and correlated layer by layer. The results show that the sweep efficiency and displacement efficiency work different effects on different layers in the severely heterogeneous reservoir. The study shows that the displacement efficiency and sweep efficiency play different roles in different layers for severely heterogeneous reservoirs. The displacement efficiency contributes mainly to the high permeability zones, the sweep efficiency to the low permeability zones, both of which contribute to the middle permeable zones. To improve the sweep efficiency in the low permeability zones is of significance for enhancing the whole recovery of the reservoir. It is an important path for improving the effectiveness of chemical flooding in the severely heterogeneous reservoirs to inject ternary combination slug after profile control.

Effect of polymer solution structure on displacement efficiency

In this paper, a series of experiments, including atomic force microscope （AFM）, environmental scanning electron microscope （ESEM）, and core displacement tests were conducted to investigate the effect of polymer solution structure on solution properties and oil displacement efficiency. The results show that in the HPAM solution polymer coils were formed and then aggregated into a loose structure, while the HAP2010 solution formed a strong network structure, which would significantly improve the solution viscosity and flow resistance so as to upgrade the capacity of piston-like oil displacement in highly permeable porous media. Meanwhile, the retention of the HAP2010 solution at pore throats were also enhanced, which could reduce water production during subsequent water flooding and enlarge the swept volume during polymer flooding. Therefore, enhancing the interaction among polymer molecules is an effective way to improve the displacement efficiency of polymer solutions in heavy oil reservoirs with high permeability.

Effect of stress sensitivity on displacement efficiency in CO_2 flooding for fractured low permeability reservoirs

Carbon dioxide flooding is an effective means of enhanced oil recovery for low permeability reservoirs. If fractures are present in the reservoir, CO2 may flow along the fractures, resulting in low gas displacement efficiency. Reservoir pore pressure will fluctuate to some extent during a CO2 flood, causing a change in effective confining pressure. The result is rock deformation and a reduction in permeability with the reduction in fracture permeability, causing increased flow resistance in the fracture space. Simultaneously, gas cross flowing along the fractures is partially restrained. In this work, the effect of stress changes on permeability was studied through a series of flow experiments. The change in the flowrate distribution in a matrix block and contained fracture with an increase in effective pressure were analyzed. The results lead to an implicit comparison which shows that permeability of fractured core decreases sharply with an increase in effective confining pressure. The fracture flowrate ratio declines and the matrix flowrate ratio increases. Fracture flow will partially divert to the matrix block with the increase in effective confining pressure, improving gas displacement efficiency.

Study on Oil Displacement Efficiency of Binary Compound Flooding in Heterogeneous Reservoir

Heterogeneous reservoir characteristics for oilfield, choose HS-1 non-ionic surfactant and polymer formation in binary combination flooding system can significantly improve the rate of production of low permeability reservoir in heterogeneous reservoir. According to the core flooding experiment analyzed longitudinal heterogeneous models, single surfactant and a single polymer and polymer flooding of table binary complex drive effect. Studies show that binary combination flooding recovery effect is best, followed by polymer flooding, minimum of surfactant flooding, in heterogeneous reservoir.

Research on Empirical Formula of Displacement Efficiency in Bohai Oilfield

Displacement efficiency is an important index of water drive oilfield. This article takes water drive oilfield as the object to analyze the influence factors of displacement efficiency in limit water cut stage of water drive oilfield. The displacement efficiency experimental data of 99 cores which come from 65 development wells of 34 oilfields have been collected. The authors use the method of multiple linear regression analysis to establish a new empirical formula of displacement efficiency. The relative error of the empirical formula is less than 7% compared to the experimental data.

Monotricat, Innovative Displacement Hull High Hydrodynamic Efficiency and Energy Recovery, Navigating at Speeds of Planing Hulls on Spray Self-produced

The need to have naval units ever faster pushed the ship design to design hull shapes with increasingly higher performance thanks to the use of lightweight materials such as aluminum, and more powerful engines, etc., but without substantially modifying the traditional forms of hull. The hull patented Monotricat high hydrodynamic efficiency and energy saving it represents an evolution of the traditional architectures of the hulls, as its shape is adapted to recover wave formation engendered from the bow and sprays associated with it so as to reduce the resistance to the benefit of the speed, and navigating in displacement at speeds of planing hulls with an efficiency of about 20%. The patented hull Monotricat represents the overcoming of distinction between displacement and planing hulls, because, unlike previous solutions, the hull conventionally called Monotricat is the first displacement hull that can navigate at both displacement and planning speeds, with a resistance curve almost straight, maintaining the characteristics of a displacement hull, since it combines the characteristics of displacement and planning hull. It presents an innovative architecture that could be defined as a hybrid between a monohull and catamaran, navigating on spray self-produced. The combination of these three types of naval hulls allows it to ensure： safety, comfort navigation, best seakeeping and maneuverability in restricted waters, stability, reduction of resistance to motion, cost management, regularity on the routes even in adverse weather-sea. These characteristics of the hull have been studied, tested and validated by leading research institutes and universities with more ameliorative results in each subsequent experimentation, reported in the present work, which demonstrated a greater hydrodynamic efficiency compared to conventional hulls of 20%.

Effects of cosolvents on CO_(2) displacement of shale oil and carbon storage

Molecular dynamics method was used to establish composite wall/inorganic nanopores of three pore sizes, three shale oil systems, five CO_(2)-cosolvent systems, and pure CO_(2) system. The process of CO_(2)-cosolvent displacement of crude oil in shale nanopores and carbon storage was simulated and the influencing factors of displacement and storage were analyzed. It is shown that the attraction of the quartz wall to shale oil increases with the degree of hydroxylation. The higher the degree of quartz hydroxylation, the more difficult it is to extract the polar components of shale oil. Nanopore size also has a great impact on shale oil displacement efficiency. The larger the pore size, the higher the shale oil displacement efficiency. The closer the cosolvent molecules are to the polarity of the shale oil, the higher the mutual solubility of CO_(2) and shale oil. The more the non-polar components of shale oil, the lower the mutual solubility of CO_(2) and shale oil with highly polar cosolvent. Ethyl acetate is more effective in stripping relatively high polar shale oil, while dimethyl ether is more effective in stripping relatively low polar shale oil. Kerogen is highly adsorptive, especially to CO_(2). The CO_(2) inside the kerogen is not easy to diffuse and leak, thus allowing for a stable carbon storage. The highest CO_(2) storage rate is observed when dimethyl ether is used as a cosolvent, and the best storage stability is observed when ethyl acetate is used as a cosolvent.

Mechanisms of oil displacement by ASP-foam and its influencing factors

ASP-foam （ASPF） is a system prepared by injecting natural gas into the conventional alkali- surfactant-polymer （ASP） system. Foam can be formed in the porous media by the interaction of gas and surfactant in the ASP system. With the ASPF system, oil recovery is improved as the interfacial tension （IFT） is reduced to a relatively low level, and the swept volume is enlarged. In this paper, four surfactants were evaluated and characterized by IFT between ASP system and oil and the foaming performance. AI- kyl benzene sulfonate （ORS-41） was chosen as the surfactant to best reduce IFT between displacement fluids and oil and improve the foaming performance. The mechanisms of ASPF flooding were studied in this paper, the results show that the ASPF flooding not only enlarges the swept volume but also enhances the displacement efficiency. The effects of reservoir heterogeneity, the gas-liquid ratio of ASPF system, and the concentrations of polymer and surfactant on the displacement efficiency were studied. A field trial of ASPF flooding has also been conducted. Both the laboratory results and the field trial results show that the ASPF flooding can significantly increase the oil recovery, with a 30% increase in the proportion of the original oil in place recovered compared with water flooding.

Numerical modelling of the dynamic process of oil displacement by water in sandstone reservoirs with random pore structures

The study aims to identify a suitable site for open and bore well in a farmhouseusing ground magnetic survey in south India.It also aims to define depth to granitoid and structural elements which traverse the selected area.Magnetic data(n=84)measured,processed and interpreted as qualitative and quantitatively.The results of total magnetic intensities indicate that the area is composed of linear magnetic lows trending NE-SW direction and circular to semi-circular causative bodies.The magnetic values ranged from-137 nT to 2345 nT with a mean of 465 nT.Reduction to equator shows significant shifting of causative bodies in the southern and northern directions.Analytical signal map shows exact boundary of granitic bodies.Cosine directional filter has brought out structural element trending NE-SW direction.Results of individual profile brought to light structurally weak zone between 90 m and 100 m in all the profile lines.Sudden decrease of magnetic values from 2042 nT to 126 nT noticed in profile line 6 between 20 m and 30 m indicates fault occurrence.Magnetic breaks obtained from these maps were visualized,interpreted and identified two suitable sites for open and bore well.Radially averaged power spectrum estimates depth of shallow and deep sources in 5 m and 50 m,respectively.Euler method has also been applied to estimate depth of granitoid and structural elements using structural indexes 0,1,2,and 3 and found depth ranges from<10 m to>90 m.Study indicates magnetic method is one of the geophysical methods suitable for groundwater exploration and site selection for open and borewells.

A way of estimating the characteristic slip displacement

During the ruptures of an earthquake, the strain energy, AE, will be transferred into, at least, three parts, i.e., the seismic radiation energy （Es）, fracture energy （Eg）, and frictional energy （Ef）, that is, AE = Es ＋ Eg ＋ El. Friction, which is represented by a velocity- and state-de- pendent friction law by some researchers, controls the three parts. One of the main parameters of the law is the char- acteristic slip displacement, De. It is significant and nec- essary to evaluate the reliable value of Dc from observed and inverted seismic data. Since Dc controls the radiation efficiency, ηR = Es/（Es ＋ Eg）, the value of qR is a good constraint of estimating Dc. Integrating observed data and inverted results of source parameters from recorded seis- mograms, the values of Es and Eg of an earthquake can be measured, thus leading to the value of ηR. The constraint used to estimate the reliable value of Dc will be described in this work. An example of estimates of Dc based on the observed and inverted values of source parameters of the September 20, 1999 Ms 7.6 Chi-Chi （Ji-Ji）, Taiwan region, earthquake will be presented.

黏弹性聚合物驱渗流机理研究进展

聚合物驱已成为国内外化学驱中提高原油采收率主要方法之一,其在大庆油田的60年开发稳产中起到重要作用,在水驱基础上提高原油采收率达到约13%.聚合物驱主要机理为改善流度比,提高注入液的波及体积,从而提高驱油效率.近几年,聚合物溶液黏弹性能够进一步扩大其在多孔介质中的微观波及面积从而提高微观驱油效率的作用机理也逐渐被人们所认识.文章从聚合物溶液黏弹特性、聚合物驱微观可视化实验、岩心驱替实验及驱油机理理论研究4个方面进行了综合分析,对比论述了国内外关于黏弹性聚合物溶液渗流机理的研究现状、实验手段及方法,给出了聚合物溶液的黏弹性产生的法向应力能够进一步对水驱后残余油产生“拉”“拽”作用,从而使其比纯黏性流体进一步提高在多孔介质内的微观波及效率及驱油效率,明确了弹性湍流是产生表观增稠的本质,对提高驱油效率产生一定的正向影响.最后针对黏弹性聚合物驱渗流机理研究面临的问题及发展方向进行总结,弹性湍流产生的条件、黏弹性对不同尺寸孔隙内不同类型原油采收率的贡献及弹性与油藏润湿性的协同影响等机理成为未来研究的挑战与方向.论文的归纳能够为黏弹性聚合物溶液机理深入研究及矿场设计优选聚合物提供重要的参考.

计算注水开发不同阶段体积波及系数的新方法

体积波及系数是油田评价开发效果、制定开发调整方案的重要依据。为了研究注水开发不同阶段体积波及系数的变化规律,从注入孔隙体积倍数角度出发,根据油水相对渗流理论与油藏工程原理,提出了驱油效率与注入孔隙体积倍数的计算模型,建立了体积波及系数计算方法,并以胜利油田3个试验区为例进行了计算与分析。结果表明:驱油效率与注入孔隙体积倍数之间满足指数方程,二者关系曲线呈上凸型;随着注入孔隙体积倍数的增大,驱油效率由最小驱油效率逐渐增大,并趋近于最大驱油效率;对驱油效率计算模型进行验证,预测值与实测值的平均相对误差仅为1.90%;水驱开发过程中体积波及系数与注入孔隙体积倍数关系曲线整体呈快升-缓升-近平台状演变趋势,计算结果能够指导开发调整措施的效果评价;3个试验区目前体积波及系数接近90%,波及区内存在大量剩余油,亟需开展波及区内主体剩余油的描述与启动方法研究。

生物化学复合提高采收率技术研究进展及发展趋势

系统调研了中外近10a来在生物化学复合提高采收率技术方面的室内研究及现场应用进展,分别从提高洗油效率和扩大波及体积2方面,就采油菌体、生物表面活性剂、生物多糖分别与表面活性剂、聚合物、纳米颗粒等化学采油制剂间的协同作用机理,体系构建及现场应用效果进行了分析。研究结果表明:生物菌体及其代谢产物与化学采油制剂复合后,在界面张力降低、乳化分散、流度比控制和稠油降黏等方面都具有协同增效作用,现场应用也取得了良好的效果,其中胜利油田探索了菌体复合聚合物调剖技术及微生物脱硫保黏技术,预测提高采收率分别为9%和10.3%,大庆油田开展生物表面活性剂三元复合驱现场应用,先导区提高采收率达到22%。生物化学复合提高采收率技术在老油田难采储量动用方面具有巨大的应用前景。下一步需继续深化生物、化学体系间协同增效机理,根据油藏平面及层间、层内的差异,创新生物、化学采油体系复合及实施工艺,细化不同开发阶段、不同油藏空间的实施方案,通过油藏立体均衡开发,最大限度发挥生物与化学复合增效技术优势,满足老油田可持续开发的需求。

纳米生物质体系性能评价及驱油特性实验研究

本文以玉米秸秆与纳米硅为原料,制备了改性纳米生物质,并评价了其在不同条件下的表面活性及界面张力。通过调整纳米生物质浓度(0.1%~1.0%)、注入速度(0.1~1.0mL·min^(-1))及注入体积(100~1000mL),优化体系的驱油参数。结果显示,纳米生物质浓度为0.8%、注入速度为0.6mL·min^(-1)、注入体积为600mL时,体系表现出最佳的驱油效率。此外,实验室结果在典型油田的现场应用中得到验证,应用优化后的体系参数,油田的日产油率从100桶提升至140桶,增幅达40%。由此可见,纳米生物质体系能够提高油田驱油效率,研究成果有助于指导油田开发中生物质材料的应用。

新型低界面张力纳米微球调驱剂的合成与性能研究

聚丙烯酰胺纳米微球调驱剂作为一种新型的纳米驱油材料,在油田提高采收率方面取得了广泛应用。但是,目前使用的聚丙烯酰胺纳米微球功能主要以封堵为主,存在单体固含量低、水溶液吸水膨胀速度过快、驱油和降低表界面张力功能较差等问题。利用反相乳液聚合法,以白油为油相,2-丙烯酰胺-2-甲基丙磺酸(AMPS)、丙烯酰胺(AM)混合单体为水相,油酸/双子聚醚/OP-10混合表面活性剂为乳化剂,根据三元相图确定油相/乳化剂/水相三相的最佳配比(质量分数)为33.93%/24.87%/41.2%,以甲叉双丙烯酰胺(MBA)作为交联剂,在35℃利用氧化-还原剂聚合获得了既具有封堵功能,又具有超低表界面张力、高洗油效率的新型纳米微球调驱剂。工艺优化实验确定最佳的合成条件为单体配比m(AM)∶m(AMPS)为8∶1,交联剂质量分数为0.1%,氧化-还原剂质量分数为0.3%,搅拌速度为450 r/min。对聚合物纳米微球进行表征和性能评价,结果表明,其固含量为20.1%,粒径为54 nm,纳米微球封堵率可达95.1%,用其0.2%的水溶液测得界面张力为0.332 mN/m,洗油效率高达89.13%,为实施油田调驱提供了一种新材料。

活性MoS_(2)纳米片剥离油膜机理研究

纳米材料可以提高原油采收率,但目前对于纳米材料的研究主要集中在球形纳米材料的性能上,对于二维片状纳米材料的研究甚少。自主合成了两亲性MoS_(2)片状纳米材料(活性MoS_(2)纳米片)用于大幅度提高水驱后原油采收率,针对活性MoS_(2)纳米片在固体表面上的铺展规律进行系列研究,阐明了活性MoS_(2)纳米片对固体表面油膜的作用机理。基于气-水-固相接触角的测量,明确了油湿性石英片在活性MoS_(2)纳米片驱油体系中浸泡120 h后,水滴平衡接触角保持90°不变,石英片表面由油湿转变成中性润湿;地层水和质量分数为0.15%的SiO_(2)纳米流体均无法使油膜在固体表面产生楔形膜,而质量分数为0.005%的活性MoS_(2)纳米片驱油体系可在油-水-固接触区域形成明显的楔形膜,产生结构分离压力,最终剥离固体表面油膜。研究发现,在质量分数为0.005%的活性MoS_(2)纳米片驱油体系中,油膜在固体表面的收缩过程中会形成内、外两条接触线,内、外接触线的收缩速度分别是0.6617×10^(-5)和8.5817×10^(-5)cm/s;从热力学角度计算出油膜在收缩过程中油-水-固混合体系Gibbs自由能的增量呈负增长,证明油膜在活性MoS_(2)纳米片驱油体系中的收缩是自发进行的。该项研究成果说明质量分数为0.005%的活性MoS_(2)纳米片驱油体系具有高效的驱油能力。

纳米淀粉流体提高原油采收率

为了进一步促进纳米驱油技术在低渗透油藏中的高效应用,亟需开发新型的纳米驱油产品。纳米淀粉颗粒作为一种环境友好型的材料,分布广、价格相对低廉、性能优异,具备大幅度提高采收率的潜力。通过室内静态实验、岩心驱替实验、微观可视化实验、CT扫描实验等手段,从纳米淀粉流体的基本物性、提高驱油效果、扩大波及体积等方面研究了其提高采收率的过程和机理。研究结果表明,质量浓度为5000 mg/L的纳米淀粉流体因其亲水性和较小的粒径(30 nm)可改变水分子的赋存状态,使水相变温度从102℃升高至110℃,使得岩石表面的润湿接触角从78°降至34.2°,使油水界面张力从20 mN/m降至0.56 mN/m,注入压力下降39.6%。在微观可视化模型中,纳米淀粉流体可以明显降低多孔介质中的含油饱和度,特别是多孔介质固体表面的油膜量明显减少,提高驱油效果明显。在低渗透岩心中,纳米淀粉溶液的驱替前沿更加均匀,与水驱相比具有更大的波及体积。由于较大的波及体积、较高的驱油效率以及良好的润湿性等,注入0.4 PV质量浓度为5000 mg/L的纳米淀粉流体后,低渗透岩心的采收率增幅达21百分点。研究结果可为低渗透油藏的提高采收率提供一种新的技术参考。

低渗油田化学驱油机制实验研究

低渗透率油藏的有效开发是提高油田采收率的关键挑战之一。通过实验方法探究了化学驱油技术在低渗透率油藏中的应用效果,着重研究了表面活性剂和聚合物溶液对驱油效率的影响。结果表明:化学驱油技术显著提高了低渗透率油藏的采收率,当表面活性剂质量分数为1.0%时,油水界面张力降至10.4 mN·m^(-1),驱油效率提高至85.3%;当聚合物质量分数为0.3%时,相对驱替效率提升至1.25倍;化学驱油能有效改善岩石的孔隙结构,使岩心样本的孔隙度从15%提升至20%,渗透率从49.5 mD增加至75.8 mD;碱性化学剂和盐类化学剂的使用能进一步提高采收率,尤其是当碱性化学剂质量分数达到1.5%和盐类化学剂质量分数达到0.3%时,采收率提高比例分别达到12.6%和13.6%。研究结果证实了化学驱油技术在提高低渗透率油藏开发效率方面的潜力,为实际应用提供了理论依据和技术支持。

基于相场法的固井顶替效率数值模拟及影响因素分析

考虑摩擦阻力、浮力、重力和两相界面张力的影响,建立基于相场法的固井顶替效率数学模型并进行数值求解,评价固井顶替效率,采用环空顶替实验进行验证,分析井斜角、前置液结构、密度差、套管偏心度和套管旋转等因素对固井顶替效率的影响。结果表明:固井顶替效率数学模型有效改善传统模型的顶替界面模糊和振荡现象,具有一定的可靠性。井斜角改变重力沿井筒方向的分力并影响顶替界面形态的发展,水平井筒顶替界面形态的稳定性最差;采用“冲洗液和隔离液”的前置液结构时,水泥浆的顶替效率更高;优选流体密度差时,顶替效率提高5%;水平井筒中,套管偏心度为0.1时,顶替效率最高,但现场应用条件难以实现;套管旋转可显著缓解水泥浆宽边指进程度。考虑施工的难易程度,提高顶替效率的措施依次为:选用“冲洗液和隔离液”的前置液结构、优选密度差、采用套管旋转的顶替方式、控制套管偏心度小于0.1。该结果可为固井顶替效率的预测和优化提供指导。