CO2辅助重力驱油开发效果影响因素分析

针对各类地质参数对CO₂辅助重力驱油技术开发效果影响规律尚不明确的问题,以某中低渗油藏为研究对象,建立多个一注一采机理模型研究地层沉积韵律、倾角、渗透率、孔隙度、垂直渗透率与水平渗透率比值、渗透率级差对CO₂辅助重力驱油效果的影响。结果表明:正韵律沉积地层相较于反韵律地层更适用于CO₂辅助重力驱油;地层倾角有利于重力分异和形成气顶;中低渗低孔油藏开展CO₂辅助重力驱油,对抑制气窜突破具有一定作用;垂直渗透率与水平渗透率比值越小,越有利于抑制气体的纵向快速扩散;渗透率级差对CO₂辅助重力驱油影响不大;不同地质因素对采出程度影响由大到小依次为垂直渗透率与水平渗透率的比值、地层倾角、地层渗透率、地层孔隙度、地层渗透率级差。A油藏矿场实践表明,CO₂辅助重力驱油能够使其阶段累计产油量提高3倍以上,可取得明显的增产效果。研究成果可为同类油田的CO₂驱开发提供理论指导。     

水驱转CO2混相驱渗流机理及传质特征

CO₂混相驱作为三次采油技术一般在注水开发之后实施,其需要考虑水驱后残留在孔隙中的注入水对CO₂混相驱的影响。基于常规PVT多次接触实验,采用带多点取样孔的长填砂管,在不同含水阶段分别开展注气驱替实验和气水交替驱实验,研究多孔介质中可动水参与下的多相多组分渗流规律以及不同含水率对油、气两相组分传质的影响。研究结果表明：在不同含水率下CO₂与原油仍能发生混相,CO₂的注入形成了新的渗流通道,扩大了水驱波及体积。但高含水率对油相和气相间组分传质有一定的抑制作用。此外,不同含水率下转CO₂驱会在储层中形成不同的油、气、水三相渗流和分布特征,从而影响采出程度,而气驱最终采收率主要受注气驱油效率和水驱波及体积共同作用的影响。     

稠油油藏CO2泡沫启动残余油机制的可视化实验

国内外对于CO₂泡沫与稠油作用的理论研究已相对成熟,但能直观表现CO₂泡沫在驱替稠油过程中对残余油的启动过程以及作用方式的可视化研究较少,为了进一步探究CO₂泡沫与稠油的作用机理,利用自制二维平面模型,通过可视化实验驱替系统开展了CO₂泡沫在驱替过程中对残余稠油启动效果的微观动态实验研究,观察了启动盲端残余油、剥蚀油膜、段塞前端乳化驱油等过程;利用高温高压配样装置,开展了CO₂泡沫体系作用下稠油的PVT实验。温度从30℃升至90℃,气体溶解度变化不大;稠油体积因子由1.19上升至1.42;降黏率由13.55%上升至67.42%。一方面,CO₂泡沫选择性封堵大孔道、启动残余油的微观作用;另一方面,CO₂泡沫流体降低了驱替系统的流度比。这两者的共同作用,使得CO₂泡沫流体具有改善波及体积、增加驱油效率的效果。     

志丹油区长7页岩油储层CO2吞吐室内实验

为了评价页岩油储层CO₂吞吐驱油效果及不同尺度孔喉下原油可动性,选取延长油田志丹油区长7储层天然岩心,基于高温高压长岩心CO₂吞吐实验和短岩心剩余油在线核磁共振实验,在评价驱油效果的基础上,分析不同测压点CO₂混相状态及驱替规律,对比纳米、微米级孔喉尺度下混相吞吐与非混相吞吐效果,评价页岩油储层不同尺度空间原油可动性。研究表明：CO₂非混相吞吐波及效果较差,岩心内部压力增加不明显,压力波及范围小;CO₂混相吞吐波及范围广,压力梯度大,单位时间产油量高,驱油效果明显好于CO₂非混相吞吐,在注入相同孔隙体积倍数条件下,采收率较CO₂非混相吞吐提高8.24个百分点;CO₂混相吞吐前2周期生产压差大,混相吞吐区间距离长,混相驱特征明显;在整个岩样孔喉中,微米级孔隙占比低,纳米级、亚微米级孔隙是原油主要贡献者。该研究成果可为页岩储层补充地层能量、提高采收率提供重要参考。     

CO2注入方式对芳48油藏开发效果的影响

大庆油田芳48断块为特低渗透油藏,对该油藏进行了水驱、CO₂驱、CO₂吞吐、CO₂转水驱、水驱转CO₂驱等开采方式室内物理模拟研究。实验结果表明,该区块水驱见水早、含水率上升快、注水能力低。在上述5种气驱方式中,CO₂吞吐后气驱的累积采收率最高,然后依次为水驱转CO₂驱、气驱、CO₂驱转水驱,CO₂吞吐的累积采收率最低。从累积气油比来看,CO₂吞吐累积气油比最高,其次为CO₂驱,而水驱转气驱、气驱转水驱、吞吐转气驱的累积气油比较低。从气体注入能力来看,气驱的注入能力最高,而水驱转气驱、气驱转水驱的注入能力比较低。考虑开采效果和气体注入能力,芳48特低渗透油藏开采应优先选择CO₂吞吐后气驱,其次为水驱转CO₂驱。     

注CO2重力驱技术在海拉尔油田高倾角断块油藏的适用性

海拉尔油田高倾角油藏石油探明地质储量规模大,地层倾角超过10°以上的储量占总探明地质储量的68.6%。受构造高差的影响,常规注水开发难以实现构造顶底部位油井均衡驱替,边底部油井含水率上升快,构造高部位油井受效差,整体开发效果不理想。针对海拉尔油田高倾角断块油藏水驱开发效果差的问题,以注CO₂重力驱油实验为基础,以油藏数值模拟为手段,开展注CO₂重力驱油机理、影响因素及适用性研究。结果表明：当以原始地层压力10.57 MPa注入1.2 PV的CO₂时,CO₂驱油效率可达55.9%,能大幅度提高高倾角断块油藏的采收率;地层倾角、储层渗透率、注气速度是影响注CO₂重力驱效果的主要因素;海拉尔油田有4 411.35×104 t石油探明地质储量适合开展注CO₂重力驱开发,注CO₂重力驱技术在海拉尔油田具有广阔的应用前景。     

CO2驱开发后期防气窜综合治理方法研究

室内实验得到的 CO₂混相驱油效率往往可达 90% 以上,但现场却难以达到室内实验的驱油效果。 限制采收率提高的主要原因是 CO₂的黏性指进、重力超覆和油层的非均质性等因素对注入 CO₂波及效率 的影响。 针对注 CO₂驱开发后期油藏气窜现象逐渐加重、开发矛盾不断加剧等问题,从开发层系、注采结 构、注入方式以及注入剖面 4 个方面开展了改善 CO₂驱开发效果的研究,并提出了细分层系、高部位注气、 水气交替注入、聚合物调剖及 CO ₂+ 泡沫驱防气窜等技术对策。 现场实施结果显示,油藏整体气油比从 2733.1 m³/m³下降到 63.84 m³/m³,日产油从注气前的 30.72 t 上升到注气后的 81.68 t。 该项防气窜综合治 理技术及经验可为类似油藏注气驱开发方案设计和后期防气窜提供借鉴。     

水驱断块油藏CO-2气顶边水双向驱油封存机理及应用

复杂断块油藏水驱后会形成高部位剩余“阁楼油”及井间剩余油,为此建立了人工CO₂气顶与人工边水组合的双向驱技术,以实现该类油藏的剩余油动用及CO₂封存。首先,建立了模拟水驱“阁楼油”及双向驱过程的物理模型及方法,开展了CO₂驱及不同渗透率条件下双向驱对比实验,明确了双向驱提高采收率及碳封存潜力。然后,基于拟合数值模型,对CO₂和N₂双向驱开展了不同油藏及注入参数的数模研究,分别揭示了双向驱驱油及封存的主要机理,对比了2种气体双向驱的差异。结果表明：双向驱的焖井过程是气顶形成及“阁楼油”置换的必要过程;高含水油藏双向驱可提高采收率20%以上,相比气驱提高8百分点以上,而封存率相比气驱提高15百分点以上;双向驱主要驱油机理为控制油气界面运移,重力分异,气顶膨胀及抽提原油组分,而主要封存机理为控制油气界面运移,重力分异及增压促溶。经矿场试验取得良好效果,研究为水驱断块油藏有效提采提压提供技术手段及参考。     

复杂断块油藏高含水期化学剂强化CO2复合驱提高采收率技术

苏北盆地洲城油田垛一段油藏含油面积小、储层分散、储量丰度低,目前处于注水开发的中后期,剩余油的量化表征及有效挖潜技术优选成为油田深度开发阶段核心工作。以高含水开发阶段复杂断块油藏剩余油挖潜及提高原油最终采收率为目标,开发了化学剂强化CO₂复合驱提高采收率技术体系（Chemicals & Carbon-dioxide,2C复合驱）。室内实验及数值模拟研究表明,水驱后注入洗油剂较大幅度降低流体界面张力,显著提高波及范围内残余油驱油效率,通过段塞式注入的CO₂的超覆作用,携带洗油剂对正韵律含油砂体高部位有效波及,改善垂向剩余油驱替效果。2C复合驱油体系通过耦合化学剂原油降黏及CO₂超覆作用扩大波及双重优势,实现高含水期驱油效率及纵向波及系数的同时提高,显著提高了原油最终采收率。     

CO2驱油及其地震监测技术的国内外研究现状

CO₂ 驱油是通过注气井将液态 CO₂ 注入到地下储层,进而驱替油气到生产井的一项特殊采油技术,它不仅能提高采收率,而且还可以封存 CO₂,减少碳排放,对环境保护和油田生产具有双重效益。 结合课题研究,在文献调研的基础上,阐述了 CO₂ 驱油技术的基本原理,总结了 CO₂ 驱油技术的国内外发展现状,对 CO₂ 驱油关键技术进行了分析,并重点对时移地震、井间地震、微地震、VSP 及 AVO 等 CO₂ 驱油地震监测技术进行了讨论,为 CO₂ 驱油技术的应用提供了依据。     

Visualization of CO2 and oil immiscible and miscible fl ow processes in porous media using NMR micro-imaging

CO₂ flooding is considered not only one of the most effective enhanced oil recovery（EOR） methods,but also an important alternative for geological CO₂ storage.In this paper,the visualization of CO₂ flooding was studied using a 400 MHz NMR micro-imaging system.For gaseous CO₂ immiscible displacement,it was found that CO₂ channeling or fingering occurred due to the difference of fluid viscosity and density.Thus,the sweep efficiency was small and the final residual oil saturation was 53.1%.For supercritical CO₂ miscible displacement,the results showed that piston-like displacement occurred,viscous fingering and the gravity override caused by the low viscosity and density of the gas was effectively restrained,and the velocity of CO₂ front was uniform.The sweep efficiency was so high that the final residual oil saturation was 33.9%,which indicated CO₂ miscible displacement could enhance oil recovery more than CO₂ immiscible displacement.In addition,the average velocity of CO₂ front was evaluated through analyzing the oil saturation prof ile.A special core analysis method has been applied to in-situ oil saturation data to directly evaluate the local Darcy phase velocities and capillary dispersion rate.     

Mutual Interactions of CO2/Oil and Natural Gas/Oil Systems and Their Effects on the EOR Process

Mutual interactions between oil and gas are critical factors affecting the gas enhancing oil recovery (EOR) process. Focusing on CO₂/oil and natural gas/oil systems, their interactions are researched and compared by extraction capacity and solubility measurement experiments. Core flood tests are also implemented to determine the effects of interactions on oil recovery. Results show that CO₂ can extract more light oil from the original and its extraction efficiency can reach 59.3% at 46 MPa, whereas that of natural gas is only 7.3%. However, heavy components content and viscosity of the residual oil processed by CO₂ increases significantly because of extraction, while natural gas does not affect the composition of the residual so remarkably. With increased pressure, solubility of CO₂ and natural gas in a light oil present a linear growth trend with similar rate, but the former is greater than the latter by about 130m³/m³. Core flood tests show that, for the continuous gas injection in the secondary oil recovery process, recovery of CO₂ flood is about 20% higher than that of natural gas due to the late breakthrough of CO₂, as most of the crude oil is produced before breakthrough.     

Effects of hydrocarbon solvents on simultaneous improvement in displacement and sweep efficiencies during CO2-enhanced oil recovery

The addition of hydrocarbon solvent such as liquefied petroleum gas (LPG) to the CO₂ stream leads to miscible conditions in reservoirs at lower pressures by reducing the minimum miscibility pressure (MMP). Under miscible conditions, improved displacement and vertical sweepout occur simultaneously. The influences of LPG concentration and composition on the displacement and sweep efficiencies during CO₂-LPG enhanced oil recovery (EOR) were investigated. Enhanced displacement efficiency was assessed through oil viscosity reduction and oil saturation change. Moreover, the miscible flooding induced by LPG addition, which resulted in increased solvent viscosity and a lower density difference between the injected fluid and reservoir oil, provided a smaller viscous gravity number, and improved the sweep efficiency, alleviating the impact of solvent gravity override. For CO₂-LPG EOR, oil recovery increased up to 52% as compared with that for CO₂ flooding. The amount of incremental oil recovery with 100% butane in the LPG was 16%, as compared with the 100% propane case. Mitigated gravity override enabled CO₂-LPG EOR to enhance sweep efficiency. Results indicated that the compositional modeling of the EOR process with the addition of LPG provided more accurate prediction on the performance of CO₂-LPG EOR.     

延长油田致密砂岩油藏CO2驱油机理研究

CO_2驱是提高低渗透油田产量、缓解温室效应的有效途径。针对鄂尔多斯盆地油藏压力系数低、原油轻质组分含量高的特点,通过PVT和最小混相压力等测试分析方法,揭示了低压、低孔、低渗油藏CO_2驱提高采收率主要机理。开展了CO_2注入储层与无机、有机物作用后的沉淀研究,表明CO_2在无机盐溶液中不会形成沉淀堵塞孔隙,CO_2与有机质作用后沉积点高于油藏压力,且注入压力越高,CO_2在地层原油中的溶解能力越强,目标区块CO_2注入后不易形成沥青质沉淀。物模驱替实验结果表明,均质岩心的采出程度明显高于非均质岩心,且随着岩心非均质性的增加,水驱采出程度、气驱采出程度及最终采出程度均明显下降。     

Asphaltene Deposition under CO2 Injection: An Experimental Study of the Bangestan Reservoir of Ahwaz Oilfield,SW Iran

Abstract

It is essential that precipitation of asphaltenes is recognized early in the planning stage of any CO₂ enhanced oil recovery (EOR) project so that appropriate testing can be performed to evaluate whether there will be a negative impact on reservoir performance. This article presents detailed evaluations of slim tube data that were obtained during CO₂ injection using a medium-gravity Iranian crude oil.

A crude oil from Bangestan reservoir of Ahwaz oilfield containing 18.2% asphaltenes with ~31.5 °API gravity was flooded by purified CO₂ (>96% CO₂) in a slim tube apparatus under 2,700 psi at 110°C. We were going to determine the minimum miscibility pressure (MMP) of the sample oil under injection of CO₂ flood, but when a CO₂ slim tube test was performed for this oil at 2,700 psi, less than half of the saturated oil in the tube was recovered, which implied that the displacement process was immiscible. At this pressure, the asphaltene deposition in the slim tube apparatus was so severe that even a pressure gradient of 6,200 lb/in² was not able to displace any fluid through the capillary tube. Therefore, we abandoned MMP determination with this sample and investigated the problem.

Due to the high percentage of asphaltenes in the sample, using the slim tube MMP as an apparatus for determining minimum miscibility pressure of CO₂ and sample oil can be misleading.     

The Evaluation of Variable-Injection Rate Waterflooding,Immiscible CO2 Flooding,and Water-alternating-CO2 Injection for Heavy Oil Recovery

Abstract

Despite the existence of studies for separate evaluation of waterflooding, immiscible CO₂ flooding, and CO₂ water-alternating gas (WAG) for heavy oil recovery, there is a lack of an experimental, comparative evaluation of these three methods. The authors conducted tests for comparative evaluation of variable-injection rate waterflood (VIWF), immiscible CO₂ flood, and CO₂ WAG. The results illustrate the (a) effectiveness of VIWF, immiscible CO₂ flood, and CO₂ WAG; (b) effect of permeability and oil viscosity on VIWF, immiscible CO₂ flood, and CO₂ WAG; (c) effect of injection rate on VIWF; and (d) effect of slug ratio on CO₂ WAG.     

Modeling crude oil gasification

Abstract

The characteristics of CO₂-gasification of crude oil under steady-state condition were studied using a simulator. The model was developed using the minimization Gibbs free energy minimization. The effects of reactor temperature and CO₂/crude oil ratio on gas composition and lower heating value (LHV) of the produced syngas were investigated. As a result, the maximum LHV was obtained at a CO₂/crude oil ratio of 0.1 and gasification temperature of 800?°C.     

Influence of pressure and CO2 content on the asphaltene precipitation and oil recovery during CO2 flooding

During CO₂ flooding, the crude oil is treated with CO₂, and meanwhile it is displaced by CO₂. Based on the two processes, the influence of pressure and CO₂ content on the asphaltene precipitation and oil recovery efficiency are systematically investigated by indoor simulation experiment. With the increase of the pressure or CO₂ content during CO₂ treatment, the amount of asphaltene precipitation can be increased to a certain value. Correspondingly, the degrees of the changes of oil-water interface, the compositions of crude oil, and reservoir permeability are positively correlated with the amount of asphaltene precipitation. However, during the process, the oil recovery has an optimal value due to the combined action of asphaltene precipitation and the improvement of flow performance of the crude oil. These conclusions can provide a basis for high efficiency development of low permeability oil reservoirs by CO₂ flooding.     

Effect of stress sensitivity on displacement efficiency in CO2 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.     

含杂质超临界-密相CO2管道输送工艺参数优化

CO_2输送作为CCUS技术实现的中间环节,承担着将CO_2从捕获地输送到封存点的重要任务,结合原油、天然气管道的经验可知,由于管道输送具有输量大、安全可靠性高、连续性强等优势,是目前最主要的CO_2输送方式。根据国外40多年的CO_2管道输送经验,由于超临界-密相CO_2具有类似于液体的高密度和类似于气体的高扩散性与低黏度,被认为是最经济的管道输送方式。以国内某油田30×10~4 t/a CCUS项目为例,采用Pipephase模拟软件对不同管径的超临界-密相CO_2管道在相同入口参数下进行模拟计算,分析研究不同管径下的管道压力、温度、密度与输送距离之间的变化规律,得出含杂质超临界-密相CO_2最优管道输送工艺参数,为后续我国CCUS项目推广和发展提供理论依据。