Utilization mechanism of foam flooding and distribution situation of residual oil in fractured-vuggy carbonate reservoirs

The development of fractured-vuggy carbonate reservoirs is extremely difficult because of the complex fractured-vuggy structure and strong heterogeneity.Foam flooding is a potential enhanced oil recovery(EOR)technology in fractured-vuggy carbonate reservoirs.Based on the similarity criterion,three types of 2D visual physical models of the fractured-vuggy structure were made by laser ablation technique,and a 3D visual physical model of the fractured-vuggy reservoir was made by 3D printing technology.Then the physical analog experiments of foam flooding were carried out in these models.The experimental results show that foam can effectively improve the mobility ratio,control the flow velocity of the fluid in different directions,and sweep complex fracture networks.The effect of foam flooding in fractures can be improved by increasing foam strength and enhancing foam stability.The effect of foam flooding in vugs can be improved by reducing the density of the foam and the interfacial tension between foam and oil.Three types of microscopic residual oil and three types of macroscopic residual oil can be displaced by foam flooding.This study verifies the EOR of foam flooding in the fractured-vuggy reservoir and provides theoretical support for the application of foam flooding in fractured-vuggy reservoirs.

Numerical analysis of water-alternating-CO_(2) flooding for CO_(2)-EOR and storage projects in residual oil zones

Residual oil zones(ROZs)have high residual oil saturation,which can be produced using CO_(2) miscible flooding.At the same time,these zones are good candidates for CO_(2) sequestration.To evaluate the coupled CO_(2)-EOR and storage perfor-mance in ROZs for Water-Alternating-CO_(2)(WAG)flooding,a multi-compositional CO_(2) miscible model with molecular diffusion was developed.The effects of formation parameters(porosity,permeability,temperature),operation parameters(bottom hole pressure,WAG ratio,pore volume of injected water),and diffusion coeffcient on the coupled CO_(2)-EOR and storage were investigated.Five points from the CO_(2) sequestration curve and the oil recovery factor curve were selected to help better analyze coupled CO_(2)-EOR and storage.The results demonstrate that enhanced performance is observed when formation permeability is higher and a larger volume of water is injected.On the other hand,the performance diminishes with increasing porosity,molecular diffusion of gas,and the WAG ratio.When the temperature is around 100℃,coupled CO_(2)-EOR and storage performance is the worst.To achieve optimal miscible flooding,it is recommended to maintain the bottom hole pressure(BHP)of the injection well above 1.2 minimum miscibility pressure(MMP),while ensuring that the BHP of the production well remains sufficiently high.Furthermore,the tapered WAG flooding strategy proves to be profitable for enhanced oil recovery,as compared to a WAG ratio of 0.5:1,although it may not be as effective for CO_(2) sequestration.

Reservoir heterogeneity controls of CO_(2)-EOR and storage potentials in residual oil zones:Insights from numerical simulations

Residual oil zones(ROZs)have large potential for CO_(2)enhanced oil recovery(EOR)and geologic storage.During CO_(2)injection,the migration of CO_(2)in ROZs controls the performance of both EOR and storage.However,it has not been clearly visualized and understood that how geological heterogeneity factors control the transport of CO_(2)in ROZs.In this study,the oil recovery performance and geologic storage potential during continuous CO_(2)injection in a representative ROZ are studied based on geostatistical modelling and high-fidelity three-phase flow simulation.We examined the influence of autocorrelation length of permeability,global heterogeneity(DykstraeParsons coefficient),and permeability anisotropy on cumulative oil recovery and CO_(2)retention fraction.Simulation results indicate that,as the permeability autocorrelation length increases,the cumulative oil recovery and CO_(2)storage efficiency decrease.This results from the accelerated migration of CO_(2)along high permeability zones(i.e.,gas channeling).The increase in global heterogeneity and permeability anisotropies can lead to low oil recovery and poor CO_(2)sequestration performance,depending on the degree of CO_(2)channeling.The net utilization ratio of CO_(2)(CO_(2)retained/oil produced)unfavorably increases with both autocorrelation length and Dykstra eParsons coefficient,but decreases with the increase in kv/kh.Such a decrease is attributed to enlarged swept volume induced by gravity override.The study provides important implications for fieldscale CO_(2)EOR and storage applications in ROZs.

Single Well Chemical Tracer Applied to Measuring Residual Oil Saturation in Shengli Oilfields

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Low gas-liquid ratio foam flooding for conventional heavy oil

The recovery of heavy oil by water flooding is 10% lower than that of conventional crude oil, so enhanced oil recovery （EOR） is of great significance for heavy oil. In this paper, foam flooding with a gas-liquid ratio （GLR） of 0.2：1 for the Zhuangxi heavy oil （325 mPa.s at 55 ℃） was performed on cores, sand packs and plate model. In sand pack tests, polymer enhanced foam flooding increased oil recovery by 39.8%, which was 11.4% higher than that for alkali/surfactant/polymer （ASP） flooding under the same conditions. Polymer enhanced foam flooding in plate models shows that the low GLR foam flooding increased oil recovery by about 30%, even when the extended water flooding was finished at 90% water cut. Moreover, it was discovered by microscopy that foam was more stable in heavy oil than in light oil. These results confirm that low GLR foam flooding is a promising technology for displacing conventional heavy oil.

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.

Developing High Water-cut Oil Fields Deeply to Enhance Their Oil Recovery

As stated above,the ultimate recovery of conventional oil in our country is estimated to be 33.6%,i.e,about 66.4%of the oil reserves cannot be recovered by water injection and may only be targeted for tertiary oil recovery or for other ty pes.of new technologics.A screening of 82 major oifields developed by water injection and an analysis of their potential showed that application of tertiary recovery technique such as polymer flooding,surfactant flooding and gas miseible flooding will inerease the oil recovery by 12.4%.The total recoverable reserve increment cor-responds to 56%of the current remaining recover-able reserves.This means that the recoverable r'eserves in OUr country can increase by more than one half by a fully tapping of the potential.Therefore,the development of tertiary recovery technology will be an important strategic measure in China's petroleum industry.

页岩油蓄能体积压裂开发效果预测与评价方法

蓄能体积压裂(以下简称蓄压)是页岩油藏提前补充地层能量、大幅提升单井产量的主要开发方式,应用广泛。通过渗吸与驱替机理结合实际生产数据统计分析,提出了根据返排率预测蓄压开发阶段最大累计产油量方法。研究结果表明:返排率30%之后,蓄压的累计产油量与返排率对数呈强线性相关,可预测压后单井最大累计产油量;该方法已经得到其他页岩油藏实际生产数据的实证,较递减曲线分析法更加准确且更具普适性,是对储层条件、压裂规模与工艺、焖排采工作制度等主客观因素的综合评价。返排率法可进一步确定液油比和合理返排速度。蓄压排采的平均返排速度控制在6~8 m^(3)(/d·km),与渗吸排油速度相匹配,能够更加高效地利用蓄压补充的弹性能量,取得较高采收率和较低的液油比。单井压后最大可采油量的返排率预测法为蓄压的经济效益评价、生产制度优化、压裂成本控制等提供了依据,对地质-工程一体化、优化井网井距和压裂设计具有重要指导意义。

英买2缝洞型油藏注水及注气提高采收率研究

针对英买2缝洞型油藏大量剩余油未被采出问题,基于典型储层结构组合特征制备了可视化物理模型,开展了注水和注气等不同开发方式的提高采收率物理模拟实验研究。通过对比不同阶段的含水率和采收率,定量分析了不同开发方式对英买2缝洞型油藏剩余油的动用效果;利用制备的裂缝孔洞模型和断溶体模型,研究底水驱后注水、注气和气水交替开发方式的可行性,并明确了进一步提高英买2缝洞型油藏采收率的合理注采方式——低注高采注水驱油方式、高注低采注气驱油方式以及气水交替注入方式,其中,气水交替可较大幅提高原油采收率。研究结果可为英买2缝洞型油藏进一步提高采收率提供支撑。

涪陵气田立体开发地质工程一体化实践

针对涪陵页岩气田一次井网开发后剩余气储量动用不充分的问题,立体开发地质工程一体化技术是提高气藏采收率,实现对剩余储量精准动用的核心手段。通过建立页岩气地质工程一体化高效开发新模式,创新形成页岩气建模数模一体化技术进行剩余气精细研究,明确页岩剩余气分布情况;通过地质工程双甜点耦合,明确穿行黄金靶窗,建立“资源+应力+天然裂缝”三位一体分层效益组合体划分标准体系;基于剩余气差异化分布形态,建立“地质—钻井—压裂—地面协同优化”钻井与压裂优化设计流程;通过实时监测进行钻井轨迹与压裂施工的动态调整,建立一体化数据共享平台及实时决策系统。立体开发地质工程一体化技术指导焦石坝区块预期采收率从12.6%提高到23.3%,立体开发区采收率达39.2%。该技术的应用使页岩气钻采投资、10×10^(8)m^(3)产能建设投资及开发成本逐年缩减,有效指导了涪陵页岩气田提高采收率与高效开发。

稠油提高采收率技术现状及发展趋势

综述了目前稠油开采的主要方式,介绍了稠油热采技术、化学驱油、二氧化碳驱油、微生物驱油以及电磁加热等稠油开采技术的现状。分析了上述稠油开发技术的优势和不足,对稠油开发方式的发展趋势进行了预测。指出兼顾效益和环保是未来稠油开发的发展趋势。热采碳排放较多,化学驱油容易带来环境污染和水处理困难等系列问题。清洁能源有利于实现稠油开发,提升稠油开采质量。

纳米材料在油田开发领域的研究及应用

可利用石油资源逐渐减少、开采难度在增大。纳米材料具有卓越的粒子尺寸和性能,通过表面改性还可在同一纳米材料上集成多种驱油功能,其被认为是解决传统提高采收率(EOR)技术所面临众多问题的潜在方案。本文主要介绍了纳米材料的制备与改性、种类,综述其在油田开发各阶段的应用与研究进展,特别是EOR方面。结合油田开发需求与纳米技术的优势,指出了纳米颗粒在EOR过程中应用的挑战和未来研究的机遇。

延长油田H区块剩余油分布规律及开发技术研究

为了更好的明确延长油田H区域剩余油的分布特征、开发潜力,以及有效的开发策略,运用油藏工程、动态监测、数值模拟相结合的方法,认识剩余油分布规律及主控因素,进一步揭示剩余油分布特征,为下一步注水开发提供理论基础。依据油藏工程及数值模拟精细描述成果,提出了能够提高采收率的合理注采比及地层压力保持水平,优选出中高含水阶段密井网下合理的开发技术,为研究区高效注水开发提供可靠的技术支撑。

沸腾床渣油加氢裂化装置投产对重油制氢装置的影响

沸腾床渣油加氢裂化装置投产后,将溶剂脱沥青装置的原料由常减压装置洗涤油和减压渣油调整为渣油加氢裂化装置未转化油,作为重油制氢装置原料的脱油沥青性质由此发生变化。对比重油制氢装置原料油性质、主要操作参数、技术经济指标、气化炉运行周期等参数,结果表明,渣油加氢裂化装置投产后,以脱油沥青为原料的重油制氢装置气化炉油气分布更均匀,气化单元有效气含量提高2.12个百分点,有效气产率提高0.20个百分点,碳转化率提高0.18个百分点,氢气产率提高1.21个百分点,吨氢标油能耗下降140 kg,装置各项技术经济指标均有较大幅度提升,气化炉烧嘴运行周期明显延长。

陆相页岩层系岩心中气态烃井场测定技术初步应用及展望

陆相页岩层系的流体分析是页岩油甜点评价的重要基础,针对岩心样品中气态烃易于散失的特性和页岩油钻井现场的需求,研发了井场岩心气态烃快速采集测定装置及方法,探讨了基于岩心气态烃分析和热解含油性分析资料快速计算视气油比和估算游离油损失的方法。研究表明,该装置适用于全直径岩心和块状样品的气态烃检测,既可以实现全直径岩心在常温、常压下逸散气态烃的采集测定,也可以测定块状岩心样品的气态烃总量,气态烃检测相对误差10%,测试结果可以转换为单位质量岩样气态烃含量。全直径岩心逸散气分析可实现岩心气态烃的非破坏式采集和测定,反映了页岩层系垂向上含油气性及其非均质性的变化特征。视气油比可反映页岩层系含油气性和可流动性的趋势,视气油比越大,代表相应页岩层系页岩油可流动性越好。利用视气油比可估算岩心经历降压降温脱气过程中游离烃的损失量,在建立岩心降温降压脱气过程的热解游离烃损失恢复方法中具有较大应用潜力。岩心气态烃井场测定技术丰富了适用于井场的岩心流体分析实验技术手段和方法,为陆相页岩层系流体评价及甜点确定提供数据支撑。

原位二氧化碳泡沫驱提高采收率实验

原位CO_(2)泡沫驱是一种很有潜力的提高采收率技术。通过原位CO_(2)泡沫驱提高采收率实验,优化了生气体系、泡沫体系以及注入参数,得到了最佳的注入量、注入速度和适用的渗透率级差范围。研究结果表明,在温度为70℃,地层水矿化度为10 000 mg/L条件下,得到可以作用于地层深部的原位CO_(2)泡沫体系,其配方为:2.1%碳酸氢铵+1.6%醋酸+9.5%氯化铵+0.1%α-烯烃磺酸钠AOS+0.1%油酸酰胺丙基甜菜碱DHSB,泡沫体积可达810 mL,泡沫综合指数为15552 mL·min。该体系形成的泡沫在油藏中部具有较高黏度和较大弹性的特性,能够有效封堵高渗通道,表现出良好的封堵能力。在渗透率级差为6左右时,原位CO_(2)泡沫体系注入速度控制在1.0mL/min左右,注入段塞量控制在0.3 PV,能够发挥最佳的调驱效果。研究还发现,该泡沫体系在渗透率级差为3.9~13.7的非均质储层中能有效提高采收率,而在渗透率级差为15.6的条件下,虽然未能显著提高低渗层采收率,但在高渗管中仍然有一定的洗油作用。本研究为原位CO_(2)泡沫驱技术的应用和优化提供了重要参考。

微观剩余油分布及提高采收率评价方法

随着常规油藏进入高采出程度和高含水“双高”阶段,剩余储量可动用性变差,稳油增产难度日益增加。为长期挖潜油藏剩余油,加强剩余油分布赋存状态及表征,全面了解剩余油分布规律成为提高原油采收率的必要前提。通过梳理国内外针对不同油藏开展的岩心分析、一维岩心驱油、微观驱油实验,并结合激光共聚焦、核磁共振成像、CT扫描成像、荧光分析等技术,从定性到定量对一到三维微观剩余油分布研究方法进行全面总结。结果表明,含油薄片分析因高保留残余油分布状态、能真实反映残余油原貌特征且技术成熟成为研究残余油分布的基本实验方法;传统岩心驱油模型是研究剩余油分布规律及提高采收率机理必不可少的实验方法,可反映真实储层情况,但只能从宏观视角分析不同因素对渗透效果的影响;真实岩心可视化模型可有效弥补传统岩心驱油模型的不足,但可视化实验装置耐高温高压有限,制作成本较高,图像处理不太清晰;微流控模型作为新兴技术,参数可控、实验重复性高,同时可将各种驱油模式下的微驱过程、流体的流动情况进行可视化展示,为评价驱油效果提供一条新途径,但简化的微观多孔模型与实际驱替实验结果仍存在一定差距。以核磁共振成像技术、X射线CT成像技术为主的成像分析技术凭借各自优势与真实岩心实验相结合,成为从微观角度有效描述剩余油分布特征的重要方法。该综述将为了解现有剩余油研究方法提供重要借鉴,为不同类型储层进行剩余油分布、高效开发、提高原油采收率等研究提供理论支撑。

薄层砂岩边底水油藏空气辅助内源微生物驱油技术

针对边底水油藏“双高阶段”零散分布剩余油如何有效动用、低成本高效微生物驱油体系如何研发、微生物驱效果评价及配套技术攻关等难题,建立微生物驱筛选图版并评价了油藏微生物驱的适应性;利用微生物分子生态学技术全面解析了油藏微生物群落结构,筛选了乳化效果好的采油功能菌株H3;通过对主要营养成分碳源、氮源、磷源的筛选,开展单因素实验和正交实验,确定了可实现原油乳化分散和抑制硫酸盐还原菌生长的复合粉激活体系;研究了底水油层“船底形”剩余油富集特征,形成了“微生物乳化+空气提效+稠化剂封堵”提高采收率驱油模式,明确了提高采收率幅度与注入菌体浓度、注入孔隙体积倍数正相关。将研究成果应用于准噶尔盆地陆梁油田薄层砂岩边底水油藏,实施“4注20采”微生物驱提高采收率矿场先导试验,注入微生物激活剂0.13倍孔隙体积,2017至2023年阶段增油5.6×104 t,采收率提高4.0个百分点,增油效果好的井主要分布在总菌浓度高、石油地质储量大、构造高部位、油层厚度大、底水薄、采出程度较高的区域。研究成果对丰富微生物驱提高采收率技术序列具有借鉴作用。

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。