二氧化碳—原油多相多组分渗流机理研究

二氧化碳与烃类体系的多相多组分渗流机理,对于深入理解实际油田注二氧化碳的驱替特征、提高采收率及地质埋存等都具有非常重要的意义。应用细管和多次接触实验以及包含相间传质的多相多组分CO₂驱油藏数值模拟模型,系统研究了CO₂—原油体系的相变规律以及多组分体系的变相态渗流特征。结果表明,,CO₂能够大量蒸发C₁₁以下的烃组分,甚至能够蒸发C₃₂等重烃组分;CO₂气驱过程是一个蒸发与凝析的混合过程, 混相带出现在气驱前缘附近;温度越高,CH₄和N₂含量越大,最小混相压力越大。     

A new correlation for predicting the minimum miscibility pressure regarding the enhanced oil recovery processes in the petroleum industry

Miscible gas injection is a promising technique to enhance the oil recovery from petroleum reservoirs. Natural gas is usually injected because of consistency between the gas and reservoir fluid composition and accessibility of the injected fluid. In this work a new correlation is presented for accurate prediction of the required minimum miscibility pressure (MMP) for multicontact miscible displacement of reservoir petroleum by hydrocarbon gas injection. Accurate estimation of the MMP is required for optimal design of recovery systems and optimization of the production economics. It is shown that the presented correlation is very accurate and reliable for predicting the MMP over wide ranges of oil and gas compositions. Comparison of the suggested correlation with the most important existing correlations shows that the presented correlation outperforms the other alternatives both in accuracy and generality.     

混相驱提高原油采收率室内实验研究

详细地叙述了混相驱提高原油采收率室内实验研究所进行的压力－组分实验、细管实验和长岩心驱替实验。通过室内试验筛选了注入溶剂，确定了在一定实验条件下注入溶剂与地层原油形成混相的最小混相压力小混相富化量，获得了注入溶剂在岩心驱替过程中的驱油效率和动态特征等方面的重要成果。     

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。     

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.     

CO_2细管模型驱油效果研究

鉴于气驱技术对开发低渗透油藏的良好效果,运用了目前最可靠的测量最小混相压力的细管实验方法,进行了对CO2气体与原油最小混相压力的预测研究.详述了细管实验的实验条件、实验方法、具体步骤与原理.分析结果得到了注采压差、采油速度和采收率随驱替压力的变化规律,并测量了原油与CO2作用的最小混相压力,给出了合理的驱替压力范围,为油藏开采提供了参考依据.     

Calculation of minimum miscibility pressure

A method is described and tested for calculation of minimum miscibility pressure (MMP) that makes use of an analytical theory for one-dimensional, dispersion-free flow of multicomponent mixtures. The theory shows that in a displacement of an oil by a gas with n_c components, the behavior of the displacement is controlled by a sequence of n_c−1 key tie lines. Besides, the tie lines that extend through the initial oil and injection gas compositions, there are n_c−3 tie lines, known as crossover tie lines, that can be found from a set of conditions that require the extensions of the appropriate tie lines to intersect each other. The MMP is calculated as the pressure at which one of the key tie lines becomes a tie line of zero length that is tangent to the critical locus. The numerical approach for solving the tie line intersection equations is described; slim tube test and compositional simulation data reported in the literature are used to show that the proposed approach can be used to calculate MMP accurately for displacements with an arbitrary number of components present.     

不同油藏压力下CO2驱最小混相压力实验研究

CO2-原油体系的最小混相压力是影响CO2驱开发效果的关键因素。随油藏开发阶段的不断深入,当油藏压力低于原始饱和压力后,溶解在原油中的溶解气会部分脱出。油藏流体组分及其高压物性也会发生变化,影响CO2-原油体系的最小混相压力,利用原始地层流体样品测试得到的最小混相压力不再适用。为此,以中国西部某油田8个典型区块为例,进行细管实验测试和多组分数值模拟,对不同油藏压力下的最小混相压力进行系统研究。与其他油田相比,研究区各油藏油样的C1摩尔含量较高,为31.12%~51.69%,平均为43.25%;C2-C6摩尔含量较低,为8.0%~18.48%,平均仅为11.3%。细管实验和数值模拟结果表明,在原始地层压力下,CO2均与8个典型区块地层原油样品发生混相驱替,但不同区块CO2驱最小混相压力差异很大,其值为17.60~41.18 MPa。当油藏压力低于原始饱和压力后,CO2驱最小混相压力主要呈微小幅度下降的趋势。随脱气压力进一步降低,油相组分构成中,C1N2摩尔含量呈递减趋势、C7+和C24+组分呈递增趋势,而中间组分(C2和C3+)摩尔含量变化较小。在各级脱气压力下,脱出气体以C1为主,中间组分摩尔含量仅在最后一级脱气压力下急剧升高。CO2-原油混相带出现在注入CO2波及前缘靠近注入端的位置,混相带随着驱替的进行而逐渐变宽。     

注气压力对气驱驱油效率影响的实验研究

通过多组细管实验,研究塔里木油田某区块原油在模拟地层温度108℃下注气压力对气驱驱油效率的影响,分析了不同注入压力下气驱驱油效率和气体突破的影响。实验结果证实：随着注气压力、注气体积增加,气驱驱油效率增加且增幅较大,表明提高注气压力可以显著提高驱油效率;且CO2与原油间最小混相压力为35．1MPa。注气压力越大,气体与原油混相程度越高,气驱越接近活塞式驱替,气体突破时间越长。     

沙一下油藏CO2混相驱替提高采收率的研究

以沙一下区块油藏为对象,研究了CO2混相驱技术可行性及提高采收率,通过PVT实验和细管模拟实验,确定了油藏原油的最小混相压力为18.41 MPa,原油采收率达90.01%。实验结果表明,注气驱达到混相压力后,注入压力对驱油效率影响不大,而在混相压力以下的近混相区,注入压力对驱油效率影响非常大。通过长岩心驱替模拟实验,对比了水驱和CO2驱替效率,结果表明CO2混相驱提高采收率达40.8%。     

The Development of a Robust ANFIS Model for Predicting Minimum Miscibility Pressure

Miscible gas injection has been considered one of the most important enhanced oil recovery techniques. Minimum miscibility pressure (MMP) is a key parameter in the design of an efficient miscible gas injection project. This parameter is usually determined using a slimtube apparatus in the laboratory. However, many attempts have been made to introduce MMP predicting correlations. In this study an adaptive neuro-fuzzy inference system (ANFIS)–based correlation has been developed to estimate the MMP values. In this model, the MMP of reservoir fluid is correlated with 27 variables containing concentrations of different components in reservoir oil and injecting gas, molecular weight and specific gravity of C₇ ⁺ in reservoir oil and also reservoir temperature. This correlation can be applied to predict the effect of each individual parameter on the MMP values.     

低渗油藏CO_2驱油混相条件的探讨

CO2与地层油能否达到混相状态对CO2驱油技术的应用效果有重要影响,界面张力法和细管实验法测量的最小混相压力(MMP)存在较大差异。岩心孔隙结构对原油相对体积及CO2密度的影响实验均说明,多孔介质的孔隙特征对流体物性参数产生较大影响,用细管实验MMP值作为油藏条件下CO2-原油体系MMP值的做法也需要理论完善。对影响CO2驱油混相条件的主要因素进行分析,认为岩石孔隙特征、地层压力以及注入流量对多孔介质中CO2-原油体系MMP有明显影响。渗透率下降,测量的MMP值也不同程度地降低;相对而言,平均地层压力较低的油藏,测量的MMP值也较低;对注入流量的研究认为优化流量可获得较低的MMP值。综合分析以上3个因素,初步建立计算多孔介质中CO2-原油体系MMP的方程。该研究将压力分布曲线进一步细化,补充了对不同压力间流体状态的描述。图7表1参11     

注气压力和注入气体对驱油效率影响的实验研究

在石油的开采中,CO2混相驱是提高采收率的一种行之有效的方法,尤其在气驱的过程中达到混相.针对吉林油田黑59区块低孔低渗油藏,开展了注气驱油效率细管实验.通过多组细管实验,研究了吉林油田油藏在不同注入压力和气体组成下注入气的驱油效率,分析了注入压力和注入气组成对驱油效率的影响.实验结果证实,注入压力对驱油效率影响明显,...     

N2对非纯CO2驱油效果的影响

N2是驱油用CO2中常见的杂质气体,N2的存在会影响最小混相压力（MMP）和CO2驱的效果.采用延长油田原油和岩心进行了细管实验和岩心驱替实验,注入4种摩尔分数分别为0,5％,10％,15％的N2与CO2混合气体,根据细管实验确定MMP;采用高于纯CO2的MMP 20％的压力和等于MMP 50％的压力进行岩心驱替实验.细管实验结果表明,N2的存在会显著增大MMP,CO2中含摩尔分数5％的N2会使MMP增大29.34％,10％会使MMP增大64.07％;岩心驱替实验表明,N2的混入对CO2驱产生了不利影响.对于CO2混相驱,N2的摩尔分数越高,采收率的提高值越低,N2的摩尔分数对非混相CO2驱的影响较小.     

注烃混相驱最小混相压力确定方法研究

确定混相压力是混相驱的一项重要工作,核心问题是最小混相压力的确定,它是确定原油与排驱气体是否能达到完全混相的一个非常重要的参数。最小混相压力的确定方法很多,文章综合分析了实验测定和理论计算的几种常用方法,并进行了相应评价,给出了各种方法的优缺点和通用性,最终得出了确定最小混相压力的较好的几种方法,为油田注烃混相驱实践提供借鉴。     

Feasibility of Gas Drive in Fang-48 Fault Block Oil Reservoir

The Fang-48 fault block oil reservoir is an extremely low permeability reservoir, and it is difficult to produce such a reservoir by waterflooding. Laboratory analysis of reservoir oil shows that the minimum miscibility pressure for CO2 drive in Fang-48 fault block oil reservoir is 29 MPa, lower than the formation fracture pressure of 34 MPa, so the displacement mechanism is miscible drive. The threshold pressure gradient for gas injection is less than that for waterflooding, and the recovery by gas drive is higher than waterflooding. Furthermore, the threshold pressure gradient for carbon dioxide injection is smaller than that for hydrocarbon gas, and the oil recovery by carbon dioxide drive is higher than that by hydrocarbon gas displacement, so carbon dioxide drive is recommended for the development of the Fang-48 fault block oil reservoir.     

低渗透砂岩油藏注CO

着重介绍了细管实验条件对最小混相压力实验确定方法测试结果的影响。通过数值模拟方法发现,当细管长度越长、细管直径越小、驱替速度越大、孔隙度越小,则得到的最小混相压力值也越小。另外,还讨论了油藏温度、注入气组成及原油的组成与性质对混相压力的影响情况。通过对比国内外注CO₂混相驱油藏与流体的条件,说明了中国原油很难实现CO₂混相的原因即地层温度高、地面油粘度大。建议开展降低最小混相压力技术及加强防止气体突破技术的研究,以解决注气过程中气体波及效率低的问题,实现较高的采收率。     

The Use of Optimization Procedures to Estimate Minimum Miscibility Pressure

An important factor in the design of gas injection projects is the minimum miscibility pressure (MMP). A new genetic algorithm (GA)–based correlation and two neural network models (one of them is trained by back propagation [BP] algorithm and another is trained by particle swarm optimization algorithm) have been developed to estimate the CO₂–oil MMP. The correlation and models use the following key input parameters: reservoir temperature, molecular weight of C⁺ ₅, and mole percentage of the volatiles and intermediate components (for the first time, the mole percentages are used as independent variables). Then results are validated against experimental data and finally compared with commonly used correlations reported in the literature. The results show that the neural network model trained by BP algorithm and the correlation that has been developed by GA can be applied effectively and afford high accuracy and dependability for MMP forecasting.     

BP神经网络预测最小混相压力

应用BP神经网络预测CO2最小混相压力,选择C5＋分子量、油藏温度、挥发油（CH4和氮气）的摩尔分数、中间油（C2-C10）的摩尔分数作为参数,用相关文献的实验结果作为样本进行训练,选取网络模型各层函数、隐含层节点数和算法得出适合的BP神经网络,结合实际细管实验的数据及相关参数修改网络输入参数应用于实际油藏,预测最小混相压力并分析相关的影响因素,指导生产和相应理论研究。     

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.