The impacts of gas impurities on the minimum miscibility pressure of injected CO_2-rich gas–crude oil systems and enhanced oil recovery potential

An effective parameter in the miscible-CO_2 enhanced oil recovery procedure is the minimum miscibility pressure(MMP)defined as the lowest pressure that the oil in place and the injected gas into reservoir achieve miscibility at a given temperature. Flue gases released from power plants can provide an available source of CO_2,which would otherwise be emitted to the atmosphere, for injection into a reservoir. However, the costs related to gas extraction from flue gases is potentially high. Hence, greater understanding the role of impurities in miscibility characteristics between CO_2 and reservoir fluids helps to establish which impurities are tolerable and which are not. In this study, we simulate the effects of the impurities nitrogen(N_2), methane(C_1), ethane(C_2) and propane(C_3) on CO_2 MMP. The simulation results reveal that,as an impurity, nitrogen increases CO_2–oil MMP more so than methane. On the other hand, increasing the propane(C_3)content can lead to a significant decrease in CO_2 MMP, whereas varying the concentrations of ethane(C_2) does not have a significant effect on the minimum miscibility pressure of reservoir crude oil and CO_2 gas. The novel relationships established are particularly valuable in circumstances where MMP experimental data are not available.

An improved correlation to determine minimum miscibility pressure of CO2–oil system

An accurate and reliable estimation of minimum miscibility pressure(MMP) of CO2-oil system is a critical task for the design and implementation of CO2 miscible displacement process.In this study,an improved CO2-oil MMP correlation was developed to predict the MMP values for both pure and impure CO2 injection cases based on ten influential factors,i.e.reservoir temperature(TR),molecular weight of C7+oil components(MWC7+),mole fraction of volatile oil components(xvol),mole fraction of C2-C4 oil components(xC2-C4),mole fraction of C5-C6 oil components(xCs-5-C6),and the gas stream mole fractions of CO2(yCO2),H2S(yH2S),C1(yC1),hydrocarbons(yHC)and N2(yN2).The accuracy of the improved correlation was evaluated against experimental data reported in literature concurrently with those estimated by several renowned correlations.It was found that the improved correlation provided higher prediction accuracy and consistency with literature experimental data than other literature correlations.In addition,the predictive capability of the improved correlation was further validated by predicting an experimentally measured CO2-Oil MMP data,and it showed an accurate result with the absolute deviation of 4.15%.Besides,the differential analysis of the improved correlation was analyzed to estimate the impact of parameters uncertainty in the original MMP data on the calculated results.Also,sensitivity analysis was performed to analyze the influence of each parameter on MMP qualitatively and quantitatively.The results revealed that the increase of xC2-C4,xC5-C6 and yH2 S lead to the decrease of MMP,while the increase of TR,MWC7+,xvol,yCO2,YC1,yHC and yN2 tend to increase the MMP.Overall,the relevance of each parameter with MMP follows the order of TR> xC5-C6> MWC7+> xvol> yH2 S> yHC> yCO2>yC1>yN2>xC2-C4.

Estimation of Minimum Miscibility Pressure for Flue Gas Injection Using Soft Experimentations

A new approach is demonstrated in which soft experimentation can be performed for MMP measurements, thus replacing the common practice of slim tube displacement laboratory experiments. Recovery potential from oil reservoirs by miscible flue gas injection was studied by slim tube and field-scale numerical simulation using two flue gases and seven crude oils sampled at different depths in three candidate reservoirs. The soft experimentations were conducted using Eclipse300TM, a three-phase compositional simulator. This study investigates minimum miscibility pressure (MMP), a significant miscible gas injection project screening tool. Successful design of the project is contingent to the accurate determination of the MMP. This study evaluates effects of important factors such as injection pressure, oil component composition, and injection gas composition on the MMP and recovery efficiency for slim tube and field-scale displacements. Two applicable MMP correlations were used for comparison and validation purposes.

Miscibility of light oil and flue gas under thermal action

The miscibility of flue gas and different types of light oils is investigated through slender-tube miscible displacement experiment at high temperature and high pressure.Under the conditions of high temperature and high pressure,the miscible displacement of flue gas and light oil is possible.At the same temperature,there is a linear relationship between oil displacement efficiency and pressure.At the same pressure,the oil displacement efficiency increases gently and then rapidly to more than 90% to achieve miscible displacement with the increase of temperature.The rapid increase of oil displacement efficiency is closely related to the process that the light components of oil transit in phase state due to distillation with the rise of temperature.Moreover,at the same pressure,the lighter the oil,the lower the minimum miscibility temperature between flue gas and oil,which allows easier miscibility and ultimately better performance of thermal miscible flooding by air injection.The miscibility between flue gas and light oil at high temperature and high pressure is more typically characterized by phase transition at high temperature in supercritical state,and it is different from the contact extraction miscibility of CO_(2) under conventional high pressure conditions.

Estimation of the minimum miscibility pressure for CO_(2)ecrude-oil systems by molecular dynamics simulation

CO_(2)injection is an effective enhanced oil recovery technique for energy security with the benefits of carbon neutrality.To reach the maximum oil recovery,the miscible condition between CO_(2)and oil needs to be maintained in the reservoir,which requires the operation pressure to be higher than the minimum miscibility pressure(MMP).There are two types of MMPs:the first-contact MMP(FC-MMP)and the multi-contact MMP(MC-MMP).In this study,molecular dynamics simulations were performed for the CO_(2)eoil interface system using two simplified digital oil models:a Bakken dead oil with four lumping components and a live-crude-oil model with 50 types of oil molecules but with no asphaltenes and heavy oil fractions.The vanishing interfacial tension method was used to predict the MMP.Different CO_(2)eoil volume ratios were considered to mimic the different degrees of vaporization.To estimate the MMP accurately and rapidly,the interfacial tension in the low-pressure regime was used for the prediction.Consequently,different MMPs were obtained,where the MMP value increased with increasing CO_(2)eoil volume ratio.FC-MMP can be predicted when the CO_(2)eoil volume ratio is sufficiently high.When the CO_(2)eoil volume ratio was approximately 9e10,MMP was closest to the actual MC-MMP value.The condensing and vaporizing mechanism was also studied at the molecular scale.Because pure CO_(2)was used,only the vaporizing effect on MMP occurred.It was found that the intermediate C2eC6 components have the main effect on the MMP calculation.This study can help to establish a computational protocol to estimate FC-MMP and MC-MMP,which are widely used in reservoir engineering.

热作用条件下烟道气与轻质原油混相规律

通过细长管混相驱替实验开展高温高压条件下烟道气与不同类型轻质原油的热混相规律研究。在高温高压条件下烟道气可以与轻质原油实现混相驱替;相同温度条件下,烟道气驱油效率与压力呈近线性关系;相同压力条件下,随温度增加驱油效率先平缓增加,然后急速增加,驱油效率快速达到90%以上,实现混相驱,驱油效率急速增加过程与稀油轻质组分随温度增加发生蒸馏相变有着密切关系;相同压力条件下,原油越轻,烟道气与原油的最小混相温度越低,越容易实现混相,注空气热混相驱替开发效果越好;高温高压条件下轻质原油与烟道气的混相更多体现的是超临界状态的高温相变特征,与常规高压条件下CO_(2)的接触抽提混相存在较大差异。

降混剂对二氧化碳在稠油中的溶解度和最小混相压力的影响

针对CO_(2)驱油过程中,稠油体系与CO_(2)难混相,最小混相压力高于地层破裂压力的问题,对CO_(2)与原油的混合体系进行了分子模拟,考察了降混剂种类和加量、温度、压力的影响。由径向分布函数得到混相过程中CO_(2)分子及沥青质分子的聚集程度,进而明确各类分子的分散状态,分析其作用机理。在此基础上,开展高温高压PVT相态实验,测定CO_(2)与原油混合体系中添加不同降混剂后的体积膨胀系数和CO_(2)溶解度,对分子模拟结果进行验证。最后,对柠檬酸三甲酯、苯甲醇、苯甲酸乙酯3种降混剂进行优选,得到最优复配配方,并通过细管实验评价其降混性能。分子模拟结果表明,柠檬酸三甲酯的降混效果最为显著,可有效增大CO_(2)分子间的聚集程度,降低沥青质分子间的聚集程度;在高压(6.90 MPa)低温(308.15 K)的条件下,降混剂更能发挥其作用。PVT相态实验结果表明,0.23%柠檬酸三甲酯的增溶与增膨作用最佳,与分子模拟结果一致。降混剂最优复配配方为80%柠檬酸三甲酯+20%苯甲酸乙酯。在原油-CO_(2)体系中加入0.23%复配降混剂,最小混相压力降幅为21.47%,CO_(2)溶解度和原油采收率提高。降混剂含有亲油的烃类基团和亲CO_(2)的酯基,不仅能与原油体系中的极性分子结合,拆散各沥青分子的聚集体,同时在双亲性能作用下,能吸附在原油与CO_(2)的界面上,降低原油与CO_(2)的界面张力,进而降低最小混相压力。

延长油田低渗油藏注CO_(2)后原油相态特征研究

为了解决延长低孔低渗油藏注水开发中后期面临水淹水窜等一系列开发矛盾问题,通过室内CO_(2)与原油PVT相态实验和细管实验测试,研究了地层原油中注CO_(2)后相态变化特征及CO_(2)与原油的最小混相压力。实验结果表明,原油中注CO_(2)后,饱和压力逐渐上升,原油膨胀能力很强,目前地层压力下地层原油的体积膨胀系数为1.2023,原油粘度的最大降幅可以达到70%以上,细管实验表明CO_(2)与地层原油的最小混相压力为22.51 MPa,原始地层压力下不能实现混相驱。该研究为延长油田注CO_(2)驱油可行性提供了理论依据,对延长低渗透油藏长期持续发展具有重要意义。

基于分子动力学方法的致密砂岩储层CO_(2)驱油研究进展

随着致密砂岩储层CO_(2)-EOR项目的不断增加,亟需对CO_(2)与致密砂岩储层流体在孔隙介质中的相互作用机理进行研究,但室内实验难以观察到CO_(2)与流体在孔隙通道中的动态过程,而分子动力学模拟则可以弥补传统实验和数值方法的不足。为此,围绕该方法在CO_(2)-EOR研究中的2大重点——界面行为与受限空间运移行为,对包括萃取、溶胀、降黏、降低界面张力、最小混相压力、润湿性等6个方面界面行为的相关研究成果进行了系统梳理,结合前人对CO_(2)与致密砂岩储层流体在受限空间中运移行为的研究成果,提出了分子动力学在致密砂岩储层CO_(2)-EOR研究中的关键科学问题。研究结果表明:①分子动力学能够很好地将CO_(2)萃取原油中—轻烃组分的过程进行可视化,建议根据原油实际组分构成分析CO_(2)的萃取能力,从而弄清CO_(2)萃取原油中各组分的优先顺序及效率;②有关CO_(2)分子对原油溶胀降黏作用的研究,大多数成果中的原油组分体系较为单一,建议根据实际储层的原油组分,系统探讨高温高压条件下CO_(2)的溶胀降黏作用;③对于CO_(2)与油水两相之间界面张力的研究更多是在体相中进行展开,而在纳米受限空间界面行为的研究还有待完善;④有关地层水在孔隙壁面的润湿性研究,对不同因素之间的协同效应影响润湿性的机理尚不明确。结论认为,随着量子力学研究的不断深入以及计算性能的日益强大,该方法可以在更大尺度上进行复杂体系的计算,以其为基础的油藏、页岩油气藏CO_(2)-EOR机理等研究将会取得较大的突破。

X区块低渗油藏CO_(2)混相驱影响因素分析

为研究X区块低渗油藏注CO_(2)混相驱的影响因素,通过开展室内实验分析注入气CO_(2)与地层流体的最小混相压力,分析接触时间、渗透率、非均质性、杂质气体对CO_(2)混相驱油的影响,为X区块低渗油藏注CO_(2)提供理论依据。实验主要得到以下结论:通过细管实验测定得到该区块的最小混相压力为17 MPa。接触时间、渗透率和杂质气体会影响CO_(2)混相驱的效果,CO_(2)与地层流体的接触时间越长,CO_(2)与地层原油的混相效果越好。低渗油藏中CO_(2)混相驱的效果优于中高渗油藏。非均质性对混相的影响较小。CO_(2)混相压力随N_(2)及CH_(4)的摩尔分数的增大而升高,随C_(2)及C_(4)摩尔分数的增加而降低,注入气CO_(2)的纯度应该在95%以上,以上分析为目标区块后续注CO_(2)混相驱油提供了理论依据。

海上低渗油田CO_(2)驱降混剂的研发与评价

针对海上低渗J油田注CO_(2)难以实现混相驱的问题,通过室内合成柠檬酸异丁酯,采用高温高压界面张力仪和细管实验仪开展了不同降混剂的界面性能及浓度优选评价实验,筛选出适合目标油田的降混剂。实验结果表明:J油田地层压力低于CO_(2)驱油最小混相压力,无法达到混相。室内合成的柠檬酸异丁酯相比乙二醇、石油醚具有更高的安全性,能有效降低最小混相压力至17.5 MPa,可以实现混相,最佳质量分数为0.6%。

经验关联式预测烃气驱MMP方法评价

最小混相压力的预测是注气可行性评价中的重要工作之一。一般地说,确定原油与烃气最小混相压力主要采用实验方法。当实验存在困难时,可采用经验法。不同的经验方法其预测精度可能存在较大差别。目前文献中对这些注烃气混相驱MMP预测的精度评价较少。在比较了多种方法后,选择了几种主要的经验关联式方法及其适用范围,选取了部分国内油田的MMP实例数据,对比了各经验关联式MMP预测精度。结果表明在注烃气混相驱MMP预测方面,Firoozabadi-Aziz关联式较为实用,精度最高。

A review of chemical-assisted minimum miscibility pressure reduction in CO_(2) injection for enhanced oil recovery

Miscible CO_(2)injection appears to be an important enhanced oil recovery technique for improving sweep efficiency and eliminating CO_(2)-oil interfacial tension resulting in up to 10%higher oil recovery compared to immiscible flooding,in addition to the environmental benefits of reducing greenhouse gas emissions through carbon capturing utilising and storage(CCUS).Moreover,this technique could be similarly applicable to natural gas and nitrogen projects to increase oil recovery and to reduce the associated gas flaring.However,miscible displacement may not be achievable for all reservoirs,in particular,reservoirs with high temperature where high injection pressure would be needed to reach miscibility which likely exceeds the formation fracture pressure.Therefore,to further achieve reservoirs’potential,there is a pressing need to explore a viable means to decrease the miscibility pressure,and thus expand the application envelop of miscible gas injection in reservoirs with high temperatures.In this work,we aim to provide insights into minimum miscibility pressure(MMP)reduction by adding chemicals into CO_(2)phase during injection.We achieved this objective by performing a comprehensive review on chemical-assisted MMP reduction using different chemical additives(e.g.,alcohols,fatty acids,surfactants)and different experimental methodologies.Previous experimental studies have shown that a fraction of chemical additives can yield up to 22%of MMP reduction in CO_(2)-oil system.Based on results analysis,surfactant based chemicals were found to be more efficient compared to alcohol based chemicals in reducing the interfacial tension in the CO_(2)-oil system.Based on the current experimental results,adding chemicals to improve the miscibility and reduce the MMP in the CO_(2)-oil system appears to be a promising technique to increase oil recovery while reducing operating cost.Selection of the effective chemical additives may help to expand the application of miscible gas injection to shallow and high temperature reservoirs.Furthermore,our review provides an overall framework to screen potential chemical additives and an injection strategy to be used for miscible displacement in CO_(2)and/or gas systems.

Experimental and simulation determination of minimum miscibility pressure for a Bakken tight oil and different injection gases

The effective development of unconventional tight oil formations,such as Bakken,could include CO_(2) enhanced oil recovery(EOR)technologies with associated benefits of capturing and storing large quantities of CO_(2).It is important to conduct the gas injection at miscible condition so as to reach maximum recovery efficiency.Therefore,determination of the minimum miscibility pressure(MMP)of reservoir live oileinjection gas system is critical in a miscible gas flooding project design.In this work,five candidate injection gases,namely CO_(2),CO_(2)-enriched flue gas,natural gas,nitrogen,and CO_(2)-enriched natural gas,were selected and their MMPs with a Bakken live oil were determined experimentally and numerically.At first,phase behaviour tests were conducted for the reconstituted Bakken live oil and the gases.CO_(2) outperformed other gases in terms of viscosity reduction and oil swelling.Rising bubble apparatus(RBA)determined live oileCO2 MMP as 11.9 MPa and all other gases higher than 30 MPa.The measured phase behaviour data were used to build and tune an equation-of-state(EOS)model,which calculated the MMPs for different live oilgas systems.The EOS-based calculations indicated that CO_(2) had the lowest MMP with live oil among the five gases in the study.At last,the commonly-accepted Alston et al.equation was used to calculate live oilepure CO_(2) MMP and effect of impurities in the gas phase on MMP change.The Bakken oile CO_(2) had a calculated MMP of 10.3 MPa from the Alston equation,and sensitivity analysis showed that slight addition of volatile impurities,particularly N_(2),can increase MMP significantly.

顺北一区超深断控油藏注天然气开发的可行性

顺北一区矿场天然气资源丰富、油藏压力高、顶部剩余油富集,具备注天然气混相驱的开发潜力。通过注气流体相态模拟实验和油藏数值模拟,从注气原油相态、混相条件、注气方式等方面,论证顺北一区注天然气混相驱开发的可行性。研究表明,注CH4原油具有饱和压力低、体积膨胀系数大、混相压力低等优势;注CH4最小混相压力约为46.80 MPa,注伴生气最小混相压力较注干气约降低4.00 MPa。回注天然气,80%以上的井组可实现混相驱替;气水交替注入可延缓气水突破时间,提高驱替相波及系数,补充地层能量和实现均衡驱替,模拟3年可提高采出程度11.2%。

Development of minimum tie line length method for determination of minimum miscible pressure in gas injection process

Gas injection process is a very important technology in enhanced oil recovery.Minimum miscible pressure is one of the key parameters in gas injection processes.Various experimental methods such as slim tube are used to measure MMP.These methods are costly and time consuming.Recently computational methods are used in order to achieve a cost-effective and reliable technique to evaluate MMP.In this work,a new methodology has been proposed for determination of MMP using the minimum tie line length method.A real mixing cell model was developed to estimate the MMP,MME and key tie lines.This method is simple,robust,and faster than conventional one-dimensional simulation of slim tube.The new mixing cells method can accurately determine the whole key tie lines to a shift,regardless of the number of injection gas and reservoir fluid components.Unlike other methods of mixing cells,this method automatically corrects dispersion by additional contacts to achieve the low variation domain of tie line slope.Also,the determination and implementation of the minimum miscibility enrichment are investigated.

海上特殊凝析气藏流体相态及混相特征

随着海上油气勘探不断向深层拓展,以近临界态近饱和、高含凝析油为特征的特殊凝析气藏越来越多,但目前对海上该类凝析气藏的高压物性及注气混相机理仍认识不清,有待进一步深入研究。以渤海特殊凝析气藏流体高压物性测试(PVT)为基础,通过开展室内注气膨胀、多次接触及长细管最低混相压力实验分析,结合注气相态数值模拟方法,模拟从油气层上、中、下部不同深度进行伴生气注入,明确了海上特殊凝析气藏的相态特征,并探索了伴生气与地层剩余油气体系的配伍性及混相机理。结果表明:海上特殊凝析气藏一旦发生压降,地层中会产生大量的反凝析液,形成带气顶的挥发油藏,恒质膨胀过程中会发生乳光效应及轻烃抽提分层现象;伴生气对降低顶部凝析气体系的反凝析伤害作用不大,降低反凝析液量小于1%,中部轻烃凝析油体系与伴生气的多次接触混相压力为26.80 MPa,伴生气与底部凝析油体系通过溶解作用存在凝析气驱混相机理的同时,通过抽提作用存在蒸发气驱混相机理,最低混相压力为41.58 MPa,亦低于地层压力,能够达到很好的混相效果。研究成果对海上特殊凝析气藏注气提高采收率意义重大,为中后期气藏高效开发设计提供了坚实可靠的理论依据。

纳米颗粒对原油-CO_(2)体系界面张力的影响

注CO_(2)开发含沥青质油藏会导致沥青质沉淀,造成储层堵塞,而注入纳米颗粒能够有效抑制沥青质沉淀。在明确原油注CO_(2)产生沥青质沉淀特征的基础上,选取不同地区4种沥青质质量分数的原油,分别测定了无机纳米颗粒SiO_(2)、金属氧化物纳米颗粒Co_(3)O_(4)和Fe_(3)O_(4)作用下的CO_(2)与原油的界面张力,并评价了原油性质对纳米颗粒性能的影响。结果表明:原油中沥青质沉淀量随压力的增加而增大,CO_(2)与原油间界面张力随压力的增加呈现出先快速下降后逐渐变缓的趋势,对应的一次接触最小混相压力也随沥青质沉淀量的增加而增大;纳米颗粒具有较高的表面活性和比表面积,能够吸附沥青质颗粒,抑制沥青质聚集,有效降低油气体系界面张力,其中纳米颗粒性能高低依次为无机纳米颗粒SiO_(2)、金属氧化物纳米颗粒Co_(3)O_(4)和Fe_(3)O_(4);纳米颗粒性能随原油黏度和沥青质质量分数的增加而变好,随原油中硫质量分数的增加而变差。研究成果为改善CO_(2)驱替效果和抑制沥青质沉淀提供了参考和借鉴。

碳中和背景下CO_(2)驱油技术研究进展

CCUS是指CO_(2)捕集、利用和封存,是解决全球气候变暖、控制CO_(2)排放的重要技术手段,CO_(2)驱油是CO_(2)利用的主要形式之一。本文阐述了CO_(2)混相驱、非混相驱和近混相驱的驱油机理、影响因素及国内外发展简况,系统整理并归纳了国内外CO_(2)防气窜及提高波及体积技术,重点介绍了水气交替技术、化学封窜剂、CO_(2)泡沫驱、碳化水驱和增稠的CO_(2)驱,包括基本做法、封气窜原理、研究进展等,探讨了CO_(2)驱油过程中存在的问题及解决对策,为碳中和背景下非常规油气的绿色开发提供理论指导和技术支持。

二氧化碳-原油体系最小混相压力预测模型

二氧化碳-原油体系的最小混相压力(CCMMP)是CO2驱油方案设计的关键参数之一。为了提高CCMMP的预测精度,利用实验测定的46个二氧化碳-原油体系最小混相压力数据,选取油藏温度、原油中的挥发组分、中间组分、C5+、注入二氧化碳中所含的甲烷、乙烷-丁烷、氮气和硫化氢的含量8个因素,运用统计与回归理论建立了8参数的CCMMP预测模型。并将本模型和已经发表的9种方法预测的46个油样的最小混相压力结果进行了对比,结果表明本模型的预测精度大幅度提高。利用该模型对吉林油田CO2驱油试验区的5口井油样的CCMMP进行了预测,并与实验结果进行了对比,相对误差范围0.05%～3.39%,进一步验证了本模型的可靠性。