Mechanism investigation of steam flooding heavy oil by comprehensive molecular characterization

Steam flooding is a widely used technique to enhance oil recovery of heavy oil.Thermal viscosity reduction and distillation effect are considered as two main displacement mechanisms in steam flooding process.However,the molecular composition understanding and contribution for oil production are still unclear.In this study,the composition analysis of the heavy oil was investigated in the core scale steam flooding process with the temperature from 120 to 280℃.The crude oil,produced oils and residual oils were characterized comprehensively by gas chromatography and high-resolution mass spectrometry.It is found that steam flooding preferentially extracts aromatics and remains more resins in the residual oil.Viscosity reduction is the dominant mechanism when steam is injected at a low temperature.Large molecular heteroatoms with high carbon number and high double bond equivalent(DBE)are eluted into the produced oil,while compounds with low carbon number and low DBE are remained in the residual oil.As the steam temperature rises,the increased distillation effect results in the extraction of light hydrocarbons from the residual oil to the produced oil.More small heteroatoms with low carbon number and low DBE enter into the produced oil,especially in the none water cut stage.The compositional difference of produced oils is characterized in DBE versus carbon number distribution of the N and O containing compound classes.This work uses a variety of composition analysis methods to clarify the steam flooding mechanism and provides a novel understanding of steam flooding mechanisms with various temperatures and production stages from the molecular perspective.

Steam Flooding after Steam Soak in Heavy Oil Reservoirs through Extended-reach Horizontal Wells

This paper presents a new development scheme of simultaneous injection and production in a single horizontal well drilled for developing small block reservoirs or offshore reservoirs. It is possible to set special packers within the long completion horizontal interval to establish an injection zone and a production zone. This method can also be used in steam flooding after steam soak through a horizontal well. Simulation results showed that it was desirable to start steam flooding after six steam soaking cycles and at this time the oil/steam ratio was 0.25 and oil recovery efficiency was 23.48%. Steam flooding performance was affected by separation interval and steam injection rate. Reservoir numerical simulation indicated that maximum oil recovery would be achieved at a separation section of 40-50 m at steam injection rate of 100-180 t/d; and the larger the steam injection rate, the greater the water cut and pressure difference between injection zone and production zone. A steam injection rate of 120 t/d was suitable for steam flooding under practical injection-production conditions. All the results could be useful for the guidance of steam flooding projects.

Analyzing the effect of steam quality and injection temperature on the performance of steam flooding

The heavy oil reservoirs are currently mainly targeted by thermal enhanced oil recovery technologies,particularly,steam flooding.Steam flooding is carried out by introducing heat into the reservoir to unlock the recovery of heavy oil by reducing oil viscosity.Several investigations were carried out to improve oil recovery by steam flooding.Most recently,high steam flooding is reported as an effective approach to improve recovery in high pressure heavy oil reservoirs.The oil recovery from steam flooding is sub-stantially affected by the steam quality and injection temperature.In this study,an attempt was made to look into the integration of parameters,i.e.steam quality and injection temperature upon steam flooding on oil recovery by using a simulation approach via ECLIPSE.The results obtained indicated that high temperature along with the moderate value of steam quality gives the best result regarding oil recovery for steam flooding in an economical way.

CO2 assisted steam flooding in late steam flooding in heavy oil reservoirs

To improve the oil recovery and economic efficiency in heavy oil reservoirs in late steam flooding,taking J6 Block of Xinjiang Oilfield as the research object,3D physical modeling experiments of steam flooding,CO2-foam assisted steam flooding,and CO2 assisted steam flooding under different perforation conditions are conducted,and CO2-assisted steam flooding is proposed for reservoirs in the late stage of steam flooding.The experimental results show that after adjusting the perforation in late steam flooding,the CO2 assisted steam flooding formed a lateral expansion of the steam chamber in the middle and lower parts of the injection well and a development mode for the production of overriding gravity oil drainage in the top chamber of the production well;high temperature water,oil,and CO2 formed stable low-viscosity quasi-single-phase emulsified fluid;and CO2 acted as a thermal insulation in the steam chamber at the top,reduced the steam partial pressure inside the steam chamber,and effectively improved the heat efficiency of injected steam.Based on the three-dimensional physical experiments and the developed situation of the J6 block in Xinjiang Oilfield,the CO2 assisted steam flooding for the J6 block was designed.The application showed that the CO2 assisted steam flooding made the oil vapor ratio increase from 0.12 to 0.16 by 34.0%,the oil recovery increase from 16.1%to 21.5%,and the final oil recovery goes up to 66.5%compared to steam flooding after perforation adjustment.

Study of steam heat transfer enhanced by CO_(2) and chemical agents: In heavy oil production

Steam flooding with the assistance of carbon dioxide (CO_(2)) and chemicals is an effective approach for enhancing super heavy oil recovery. However, the promotion and application of CO_(2) and chemical agent-assisted steam flooding technology have been restricted by the current lack of research on the synergistic effect of CO_(2) and chemical agents on enhanced steam flooding heat transfer. The novel experiments on CO_(2)–chemicals cooperate affected steam condensation and seepage were conducted by adding CO_(2) and two chemicals (sodium dodecyl sulfate (SDS) and the betaine temperature-salt resistant foaming agent ZK-05200).According to the experimental findings, a “film” formed on the heat-transfer medium surface following the co-injection of CO_(2) and the chemical to impede the steam heat transfer, reducing the heat transfer efficiency of steam, heat flux and condensation heat transfer coefficient. The steam seepage experiment revealed that the temperature at the back end of the sandpack model was dramatically raised by 3.5–12.8 °C by adding CO_(2) and chemical agents, achieving the goal of driving deep-formation heavy oil. The combined effect of CO_(2) and SDS was the most effective for improving steam heat transfer, the steam heat loss was reduced by 6.2%, the steam condensation cycle was prolonged by 1.3 times, the condensation heat transfer coefficient was decreased by 15.5%, and the heavy oil recovery was enhanced by 9.82%. Theoretical recommendations are offered in this study for improving the CO_(2)–chemical-assisted steam flooding technique.

Quantitative description of steam channels after steam flooding

Steam channeling is one of the main barriers for EOR after steam flooding.In order to enhance the oil recovery in steam flooded reservoirs,steam channel volumes should be precisely known.In this paper,a set of methods has been established in order to study steam channeling quantitatively by using dynamic data.Firstly,steam channeling wells are identified through curves of watercut and temperature.Then,considering the hysteresis phenomenon,channeling relations are identified with the correlation coefficients between injection wells and production wells under different conditions.Lastly,an analytic model,in which steam condensation,pressure and temperature are considered,is established to calculate the steam channel volumes.A production well named L31615 in some block in Henan Oilfield in China is systematically analyzed by using the method established.The whole block is further analyzed,and the distribution map of steam channels and the steam channel volumes are obtained.The results show that steam channeling does not only occur inside a well group,but also sometimes occurs between wells in different well groups.The calculation of the steam channel volumes provides a theoretical basis for bringing a remedial action like plugging into operation.

页岩油藏提高采收率技术现状、瓶颈及对策

介绍了页岩油的储量分布、成因及赋存机理,详细概述了页岩油早期勘探、储层改造及后期提采等不同阶段的开发现状。在此基础上,着重综述了当前国内外页岩油藏提高采收率主体技术的应用现状及进展,深入分析了不同页岩油提采技术的优势与不足,同时给出了针对理论认识、技术及经济壁垒的相应策略,最后从不同角度入手,展望了今后页岩EOR的发展前景。

稠油含油污泥凝固剂研制与性能评价

针对稠油开采过程中产生的含油污泥污染环境的问题,以烧黏土、硬石灰为主要原材料研制了含油污泥凝固剂,并以含油污泥凝固剂和含油污泥为主要成分,配制了可在油层凝结固化的含油污泥调剖堵水剂,以达到含油污泥无害化和资源化利用的目的。采用XRD检测和抗压强度测试等手段,对含油污泥调剖堵水剂封堵性能影响因素进行了分析和优化,并评价了其调剖堵水性能。研究表明:该调剖堵水剂具有较长的凝胶时间、良好的施工安全性、可泵注性和适当的结构强度等优点;当含油污泥凝固剂质量分数在17%以上时,岩心封堵率达到98%以上,突破压力在20 MPa以上,具有较高的封堵强度;同时该调剖堵水剂也是一种固体废弃物资源化利用新技术,符合循环经济、绿色发展要求。含油污泥凝固剂技术有效解决了含油污泥外排造成的环境污染问题,为油田综合治理、降低生产成本提供了一种新手段。

多层砂岩油田热采油藏管理提高采收率

概述了美国科恩河油田多层砂岩稠油油藏的特征和开发历史,重点讨论了强化热采油藏管理提高采收率的实践。科恩河油田为水动力圈闭的单斜油藏,蒸汽驱开采后期,碳氧比能谱测井、四维时移热采动态及注采井动态监测结果,孤立单河道砂体识别、追踪,全油田三维地质建模及数值模拟研究为识别剩余油和提高采收率提供了依据。人工智能、蒸汽泡沫驱、双油管完井分层注蒸汽等措施扩大了蒸汽驱波及体积。加密井、水平井钻井及浅部油藏侧钻水平井可大幅度增加可采储量,水平井产量达到相邻直井的3倍以上。为开采油藏下倾部位油水界面附近未动用的“冷油藏”,在下倾部位水层钻产水井泄压,使蒸汽驱得以有效波及到该部位剩余油。

CO_(2)对稠油油藏的物性调控及辅助蒸汽驱提高采收率

为提高稠油油藏蒸汽驱后期开发效率,聚焦“双碳”背景下CCUS-EOR(碳捕集利用和封存体系提高采收率)技术的应用,以克拉玛依油田J6区为研究对象,通过对CO_(2)作用前后的稠油四组分分析,测试饱和压力、膨胀系数、黏度和密度变化情况,探究CO_(2)对稠油物性的调控效果;通过并联岩心物理模拟实验研究CO_(2)辅助蒸汽驱提高采收率效果。研究结果表明:稠油黏度主要受胶质和沥青质含量影响,稠油随着CO_(2)溶解气量的增加,饱和压力由2.08 MPa上升至11.11 MPa,膨胀系数总体呈上升趋势,上升7.6%;同时,黏度降低30.5%,密度减小3.5%。表明CO_(2)在提高饱和压力的同时,通过优化膨胀系数、黏度和密度,有效改善了稠油物性。此外,采用CO_(2)辅助蒸汽驱后,在CO_(2)溶解降黏、破乳的作用下,稠油采收率从38.55%提高至46.46%,相比纯蒸汽驱提高了7.91%。为CO_(2)辅助蒸汽驱提高稠油采收率的应用提供了理论和实验基础,可为同类型稠油油藏提高采收率提供借鉴。

Organic bases as additives for steam-assisted gravity drainage

Steam-assisted gravity drainage(SAGD)is a mature technology for bitumen recovery from oil sands.However,it is an energy-intensive process that requires large amounts of steam to heat and mobilize bitumen.The purpose of this work is to develop ways to enhance SAGD performance through the use of organic base additives.The research is approached from three focus areas that supplement and guide each other:characterization tests,sand-pack floods,and computational simulation.A number of key mechanisms for enhancing oil recovery were identified,high-temperature additive characterization tests were developed,and promising alkalis were tested in porous media.Simulation was employed to history-match sandpack flood production data,in order to demonstrate the effect of an additive on the oil–water relative permeability.Based on these results,it was concluded that oxygenated organic bases had the most potential for improving bitumen recovery through reducing the oil–water interfacial tension(IFT)by increasing the pH of the system.These organic bases favorably modify the interfacial energies between the immiscible oil–water phases and enable them to flow easily through the porous media during production.Sand-pack flood tests have successfully demonstrated a 10%–15%improvement in bitumen recovery,over baseline,in the presence of IFT-reducing additives.Simulation results further showed that an IFT reduction had a positive impact on SAGD performance.This work demonstrates the potential of organic bases to improve not only SAGD,but other steam injection processes.Furthermore,a number of experimental methods were developed,tried,and tested during the course of this work.

浅薄层稠油蒸汽驱中后期过渡注汽方式优化——以春风油田排612区块为例

为解决稠油油藏开发过程中,连续汽驱转间歇汽驱过渡期出现的热利用率不高、蒸汽带不饱满等问题,基于油藏工程理论,采用数值模拟的方法对蒸汽驱中后期的过渡注汽方式进行对比计算。结果表明,脉冲注汽和变速注汽相较于连续注汽的热利用率更高,可有效驱替残余油。根据新疆春风油田排612区块实际地质情况,建立数值模型,对蒸汽驱生产前期的部分高汽窜井进行控关调控,研究中后期2种过渡注汽方式的最佳注汽参数,得到脉冲注汽的周期为注汽5 d停注1 d、注汽速度100 m^(3)/d时开发效果最好,变速注汽的变速时间50 d、每个变速周期的注汽速度分别为50、80、110 m^(3)/d时区块开发效果最佳,对比后得出变速注汽为目标区块过渡注汽方式的最优选择。该方式不仅可有效改善储层动用程度,同时能有效恢复底层压力,为后续间歇注汽提供能量,从而进一步提高目标区块采出程度。

海上油田水平井蒸汽驱工艺研究与先导试验

为探索海上非常规稠油多轮次热采吞吐后有效接替开发方式,以渤海A油田Bm井组为例首次开展了海上油田水平井蒸汽驱先导试验。针对蒸汽驱开发面临井筒安全控制要求高、汽窜防治难度大、设备吊装摆放困难等问题,开展了水平井蒸汽驱关键工艺研究,包括水平井蒸汽驱注热安全控制工艺、高温堵调工艺等,并试制了一套适用于海上的小型化/分段卧式过热蒸汽锅炉及配套水处理设备。水平井蒸汽驱先导试验项目于2020年6月进行现场实施,过热锅炉及配套水处理设备运行平稳,水平井蒸汽驱井口、井下管柱工具性能稳定,现场通过注入泡沫段塞实现了液流调控和化学堵调增效的目的。截至2022年12月底,先导试验累产油20.70×10^(4)m^(3)、累增油5.97×10^(4)m^(3),取得了良好的增油效果,为后续渤海油田蒸汽驱扩大应用奠定了基础,可为海上稠油热采高效开发提供借鉴。

基于CT扫描的蒸汽驱岩心孔隙结构特征及相渗分析

为明确蒸汽驱对疏松砂岩稠油油藏孔隙结构特征的影响,以LDB油田为例,应用CT技术扫描不同蒸汽驱阶段岩心,构建三维数字岩心模型,提取孔隙网络模型,获取不同蒸汽驱阶段的岩心孔隙度、绝对渗透率及孔隙结构相关特征等参数,并通过流动模拟得到相对渗透率曲线,开展定量统计及分析。结果表明:随着蒸汽驱的进行,岩心孔隙空间变大,平均孔隙半径、平均喉道半径、孔隙度及渗透率均增大,渗流能力变强,孔隙结构得到改善。研究成果可为稠油油藏蒸汽驱开发设计提供技术支持。

稠油油藏CO_(2)与化学剂协同强化蒸汽驱机制

为解决单一注蒸汽开发技术难以突破在稠油深部的携热运移问题,提出加入CO_(2)与化学剂协同辅助注蒸汽开发技术。该技术不仅可降低蒸汽无效散热,还能扩大蒸汽携热运移距离。同时,以CO_(2)辅助蒸汽热采并用于稠油开发的方式可有效捕获和封存CO_(2),有助于控制温室气体排放。结果表明:CO_(2)与化学剂注入后能够吸附在蒸汽冷凝介质表面形成隔热膜,阻碍蒸汽与传热介质间的热交换,“缓释”蒸汽热量,增加蒸汽携热运移距离,从而起到动用深部地层原油的目的;CO_(2)与化学剂协同作用下,蒸汽热损降低了5.48%,采收率提高了14.5%;研究结果可为气体与化学剂辅助蒸汽驱开发方式的优化提供理论指导。

重力泄水辅助蒸汽驱开采机理及油藏工程设计

针对辽河油田稠油区块蒸汽吞吐后期产量低、转换开发方式难度大的问题,按照“垂向泄水提高热效率、直平采液提高采注比、水平井注汽提干度、注采泄稳定控制扩波及”的技术思路,开展重力泄水辅助蒸汽驱油藏工程研究,进一步明确开采机理并明确了各阶段开发特征,并对油藏工程关键参数进行优化设计。研究表明:采用上下叠置水平井与直井组合的立体井网,实现了平面蒸汽驱替、垂向重力泄水的渗流模式;重力泄水辅助蒸汽驱立体井网可为蒸汽腔的形成创造良好的条件,有效缓解了深层、特-超稠油埋藏深、沿程热损失大造成的井底蒸汽干度低、注采不同平衡等系列矛盾;重力泄水辅助蒸汽驱可划分为直井、水平井井间热连通,重力泄水辅助蒸汽驱驱替阶段和蒸汽驱调整3个阶段;重力泄水辅助蒸汽驱现场试验取得较好的开发效果,预计汽驱结束采收率可达到58.6%,为深层-特深层稠油开发方式转换提供了新途径。研究成果为同类油藏进一步提高采收率提供了借鉴。

稠油油藏多相协同蒸汽驱物理模拟实验

针对稠油油藏蒸汽驱后期纵向矛盾突出、高渗层汽窜严重等问题,以新疆油田九6区稠油油藏为例,开展多介质辅助蒸汽驱物理模拟实验研究,首先评价凝胶的成胶性能和降黏剂的降黏效果,然后使用全直径岩心对多相协同蒸汽驱的组合方式进行优化。结果表明:凝胶成胶封堵高渗层后,后续注入的多相介质可有效进入低渗层,驱动低渗油藏剩余油;注入降黏剂后,再注入N_(2)可有效增强原油的弹性能量和流动性,有助于扩大蒸汽波及体积;调堵—降黏—增压的多相协同蒸汽驱开发模式是最佳的组合方式,可提高采收率23.65个百分点。研究成果可为改善稠油油藏蒸汽驱后期开发效果提供技术借鉴。

溶剂辅助蒸汽驱后期提高稠油采收率研究

以辽河油田杜84块兴Ⅵ组超稠油油藏为对象,根据SAGD蒸汽汽腔操作压力,筛选与蒸汽露点温度相近的己烷作为辅助溶剂,进行单管驱替实验。研究了不同温度下,溶剂类型和浓度对稠油的降黏效果,并对比了不同浓度的己烷辅助蒸汽驱与纯蒸汽驱的驱油效率。实验结果分析了溶剂辅助对蒸汽驱后期的油汽比,剩余油饱和度和最终采收率的影响,揭示了蒸汽温度和溶剂浓度对蒸汽驱效率的影响规律。研究结果可为SAGD开发后期提高稠油开采效率、优化现场操作参数提供理论支持。

海上蒸汽驱安全长效注汽工艺研究及应用

对于海上蒸汽驱先导试验而言,长期高温高压工况下如何保障套管和水泥环的安全、井筒完整性及注汽效果,是蒸汽驱长期稳定运行的关键一环。为此,开展了耐高温密封胶筒与金属密封结构及室内试验研究,攻克了适用海上热采井高低温交变工况的长效密封技术难题,研制了高温井下安全阀、高温封隔器、温敏封隔器及井下光缆穿越转换器等关键核心工具,形成了集“井筒高效隔热+安全控制+光纤监测+水平段均匀注汽”多功能于一体的海上蒸汽驱安全长效注汽工艺。现场试验结果表明,形成的安全长效注汽管柱及配套工具在井下经受长达630 d的高温高压及冷热交变考验后,其远程安全控制、高效隔热以及光纤监测功能依然稳定、有效。截至2022年12月,试验井组累计产油超20万m^(3)、累计增油近6万m^(3),取得了良好的增油效果。研究结果可为首次海上蒸汽驱先导试验安全、平稳运行提供有力支持与保障,具有较好的应用前景和潜力。