考虑扩散的CO2驱多相多组分分区渗流模型

在注CO2开采原油的过程中,当注入井井底压力高于最小混相压力时,注入气与原油体系达到混相,流体的渗流阻力降到最低,大幅度地提高了原油采收率.此过程中,存在混相驱区域和非混相驱区域;同时注入气与地层流体之间存在分子间的扩散作用.从相平衡和物质平衡规律出发,利用达西线性渗流定律,推导出传统的注CO2多相多组分渗流数学模型.在此基础上,考虑CO2的扩散作用,首次推导出考虑扩散的CO2非混相驱和混相驱多相多组分的分区渗流数学模型.     

流固耦合多相多组分渗流数学模型的建立

根据流固耦合渗流的基本思想，首次建立了流固耦合渗流的运动方程，并在此基础上建立了流固耦合多相多组分渗流的数学模型，为流固耦合渗流油藏数值模拟奠定了理论基础。     

大庆油田二氧化碳驱油最小混相压力预测

本文综合分析了见诸国外文献的18种二氧化碳驱油最小混相压力预测方法的应用条件。不同油田的原油性质不同,要得到符合实际的最小混相压力预测值,必须根据应用条件认真选用适合本油田原油的预测公式。本文在分析对比各种公式的基础上,找出了适用于预测大庆油田石蜡基原油与二氧化碳最小混相压力的Silva方法。     

改进的CO2-原油最小混相压力计算模型

利用试验测定的多个油田CO2-原油最小混相压力(MMP)数据,建立了改进的MMP预测模型,并将该模型与其他模型进行了对比。结果表明,改进模型相比于其他模型具有更高的计算精度和稳定性,尤其在20～30MPa的混相压力范围内比其他模型计算精度更高,平均误差仅为2.32%。对国内外35个典型的陆相和海相原油组分组成及相应MMP的统计分析发现,由于陆相原油组分中C2～C6的平均含量要明显低于海相的,重组分C1+6的含量又明显高于海相的,导致CO2与陆相原油的MMP明显高于海相原油的。利用该模型对吉林油田和胜利油田不同区块油样的CO2驱最小混相压力进行了计算,其计算值与试验值的误差均在平均误差之内,验证了改进的模型对我国陆相油田原油的适用性。     

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。     

CO2与原油混相及非混相条件下渗流机理差异

在CO2的资源化利用获得广泛认识的同时,CO2提高采收率技术得到深入发展.研究CO2驱替过程中气、液组分变化有利于发现CO2-原油混相或非混相状态对渗流特征影响的原因.采出程度、含水及气油比等变化规律显示CO2在孔隙中具有独特的渗流特征.相同驱替量的情况下,非混相状态较早进入含水快速上升期,采出程度平缓增长,而混相状态的采出程度则保持较长时间的线性增长.组分分析结果显示, CO2驱替过程中油、气组分变化具有相似的变化规律.除此之外,混相状态的 CO2易于与油相组分作用,而非混相状态的CO2则偏向于与气相组分作用,说明混相或非混相状态时CO2与原油的作用方式不同.     

酯类化合物降低原油与二氧化碳体系最小混相压力实验

针对试验区近井地带达到混相驱、远井地带尚未达到混相驱的问题,通过注入油溶性表面活性剂(柠檬酸异丁酯或柠檬酸异戊酯)来降低原油与二氧化碳体系的最小混相压力,该表面活性剂既能够溶于原油中降低原油黏度,又能够溶解在超临界二氧化碳中降低原油与二氧化碳之间的界面张力,从而降低原油与二氧化碳之间的最小混相压力。采用长细管驱替实验的方法,测定了2种油溶性表面活性剂对试验区原油与二氧化碳体系的最小混相压力的影响。实验表明,注入的油溶性表面活性剂能够明显降低试验区原油与二氧化碳体系的最小混相压力,2种表面活性剂降低的最小混相压力值分别为7.2 MPa和6.6 MPa,并且随着表面活性剂注入段塞的增大,测得的原油与二氧化碳体系的最小混相压力逐渐降低,但是降低幅度越来越小,结合表面活性剂制备价格,得到最经济的表面活性剂注入段塞量为0.003 PV,并建议选择柠檬酸异丁酯作为试验区降低最小混相压力的化学试剂。     

复合驱油体系物理化学渗流机理研究

复合驱油体系内含有各种化学剂,这些化学剂与油层岩石间的相互作用及化学剂在各相中的分配与化学反应,都会影响到复合驱物理化学渗流的机理和规律.在前人研究的基础上系统的阐述了复合驱油过程中的物理化学作用和驱油机理;此外,将复合驱过程中的物理化学影响因素归纳为几个等效因素,可以将复合驱物理化学渗流方程归纳为带吸附作用的对流扩散方程.结果表明：复合体系在亲水和亲油多孔介质中的驱油渗流机理有很大的不同.亲水条件下,复合体系驱油的主要特征是原油被驱油体系夹带运移通过喉道;亲油条件下,复合体系驱油的主要特征是体系进入孔隙与原油形成油包水型乳状液,并可变形通过喉道.给出的渗流方程可用来预测化学剂的传输规律.     

流固耦合多相多组分渗流数学模型的建立

根据流固耦合渗流的基本思想,首次建立了流固耦合渗流的运动方程,并在此基础上建立了流固耦合多相多组分渗流的数学模型,为流固耦合渗流油藏数值模拟奠定了理论基础。     

杂质气体对二氧化碳驱最小混相压力和原油物性的影响

注入二氧化碳中混有的杂质气体会不同程度地影响二氧化碳驱最小混相压力和原油物性。研究杂质气体含量对二氧化碳驱的影响对制定合理有效的开发方案具有重要意义。利用数值模拟方法,在原油PVT数据拟合的基础上,研究了甲烷与氮气这2种杂质气体的含量对二氧化碳驱最小混相压力的影响,分析了杂质气体对二氧化碳驱原油物性的影响。结果表明,甲烷与氮气会不同程度地增大二氧化碳驱最小混相压力,且氮气对最小混相压力的影响更显著。当注入气的摩尔分数为60%时,纯二氧化碳气体可使原油粘度降低71.9%,体积膨胀系数达1.42;含30%摩尔分数的甲烷注入气使原油粘度降低69.72%,体积膨胀系数为1.41;而含30%摩尔分数氮气的注入气使原油粘度降低65.92%,体积膨胀系数为1.36。对于目标区块,注入二氧化碳中甲烷的临界摩尔分数为5.6%,氮气的临界摩尔分数为2%。     

用界面张力法测定CO2与原油的最小混相压力

采用悬滴法,测定了在模拟地层温度为356.5K、压力为8.54~23.43MPa时的CO₂与原油间的界面张力.实验发现,CO₂与原油间的界面张力随压力的增加近似呈线性下降趋势.对该数据进行了线性回归,并用外推法计算出当界面张力为零时的最小混相压力为24.17MPa,与实验观测达到一次接触混相状态时的压力(23.43MPa)相比,相对误差为3.16%.采用界面张力确定CO₂与原油间的最小混相压力,既可通过直接观测接触混相状态确定,也可利用所测界面张力数据进行估算,操作简单易行,且耗时少.     

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.     

大庆长垣外围特低渗透扶余油层CO2驱油试验研究

大庆长垣外围特低渗透的扶余油层有3.7×10⁸t储量在常规注水开发条件下不能经济有效动用。以探索适合扶余油层地质特点的经济有效开采方式和提高单井产量、采收率为目标，采用室内实验和数值模拟的综合方法进行了CO₂驱油问题的研究。通过实验测定了扶余油层CO₂驱替的相关参数，对几种驱替方式进行了比较；根据相关参数，利用数值模拟方法，对扶余油层CO₂驱油矿场试验方案进行了优化，制定了矿场实验的注入方案。室内实验结果和矿场试验生产动态综合分析表明，CO₂非混相驱油适应于大庆长垣外围特低渗透扶余油层，但由于试验区油藏的非均质性导致气窜严重。因此，抑制气窜，提高波及效率是扶余油层改善CO₂驱替效果的关键。     

特低渗透油藏CO2驱油多相渗流理论模型研究及应用

根据一系列实验成果,对特低渗透油藏CO₂驱油渗流数学描述进行了理论研究,建立了特低渗透油藏CO₂驱油渗流数学模型。该模型能反映特低渗透储层CO₂混相和非混相驱油过程中油和CO₂的混相作用以及水、油、溶剂(CO₂)的相互作用与传输、质量的相互转换,包括对流扩散、质量转换和气、液间的转换,并能反映各相流体的非达西渗流、相对渗透率及有效黏度等特性。运用该模型在扶杨油层进行了注CO₂开发试验,取得了较好效果。     

用于集输管线的0.5Cr 钢在模拟塔里木油田环境中的H2S/CO2 腐蚀行为研究

运用腐蚀失重和四点弯曲实验,参照NACE 0177-2005标准研究了用于集输管线的0.5Cr 钢在模拟塔里木油田腐蚀环境中的H₂S/CO₂腐蚀行为。结果表明,0.5Cr 钢在CO₂腐蚀环境中具有极高的均匀腐蚀速率,H₂S腐蚀性气体的存在显著降低了材料的均匀腐蚀速率。在CO₂分压为2MPa、H₂S分压为0.5MPa 时,腐蚀速率仅为0.1523 mm/a,表现出良好的抗均匀腐蚀和局部腐蚀能力。在H₂S和CO₂共存的环境条件下,0.5Cr 钢表面的腐蚀产物为FeS,未出现CO₂腐蚀产物成分FeCO₃。在该模拟条件下,H₂S的腐蚀占主导作用。同时模拟油田工况条件的抗H₂S应力腐蚀开裂实验表明,0.5Cr 钢具有良好的抗H₂S应力腐蚀开裂能力。     

CO2注入对储层多孔介质及赋存流体性质影响实验研究

明确CO2注入对储层多孔介质及赋存流体性质的影响规律是分析油藏条件下CO2驱油机理和确定提高采收率潜力的基础。开展了不同压力条件下CO2与岩心静态接触实验和岩心驱替实验,测试了CO2注入前后岩心物性及微观孔喉结构和地层流体主要离子含量、采出原油组分、黏度及其沥青质含量等特征参数。实验结果表明:CO2注入压力由5 MPa升至20 MPa过程中,储层多孔介质平均孔隙度增大19.16%,平均渗透率降低11.23%,直径为100~150μm的孔隙空间增加9.73%,直径小于1.5μm的喉道空间增加15.83%,岩心亲水性显著增强;随着CO2在不同压力下的逐渐注入,地层水中Ca^2+和HCO-3含量增大,采出原油中C 5~C 33组分含量呈现先增大后基本不变的规律,采出原油黏度及其沥青质含量呈现先迅速降低,后保持不变的规律。     

Exploitation of fractured shale oil resources by cyclic CO2 injection

With shale oil reservoir pressure depletion and recovery of hydrocarbons from formations, the fracture apertures and conductivity are subject to reduction due to the interaction between stress effects and proppants. Suppose most of the proppants were concentrated in dominant fractures rather than sparsely allocated in the fracture network, the fracture conductivity would be less influenced by the induced stress effect. However, the merit of uniformly distributed proppants in the fracture network is that it increases the contact area for the injection gas with the shale matrix. In this paper, we address the question whether we should exploit or confine the fracture complexity for CO₂-EOR in shale oil reservoirs. Two proppant transport scenarios were simulated in this paper: Case 1—the proppant is uniformly distributed in the complex fracture system, propagating a partially propped or un-propped fracture network; Case 2—the proppant primarily settles in simple planar fractures. A series of sensitivity studies of the fracture conductivity were performed to investigate the conductivity requirements in order to more efficiently produce from the shale reservoirs. Our simulation results in this paper show the potential of CO₂ huff-n-puff to improve oil recovery in shale oil reservoirs. Simulation results indicate that the ultra-low permeability shales require an interconnected fracture network to maximize shale oil recovery in a reasonable time period. The well productivity of a fracture network with a conductivity of 4 mD ft achieves a better performance than that of planar fractures with an infinite conductivity. However, when the conductivity of fracture networks is inadequate, the planar fracture treatment design maybe a favorable choice. The available literature provides limited information on the relationship between fracture treatment design and the applicability of CO₂ huff-n-puff in very low permeability shale formations. Very limited field test or laboratory data are available on the investigation of conductivity requirements for cyclic CO₂ injection in shale oil reservoirs. In the context of CO₂ huff-n-puff EOR, the effect of fracture complexity on well productivity was examined by simulation approaches.     

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。     

CO2 sequestration through enhanced oil recovery in a mature oil field

Recent advances in enhanced oil recovery (EOR) technology create new opportunities for CO₂ sequestration. This paper proposes a technical–economic model for underground storage of CO₂ emitted by a fertilizer industry in the Northeast of Brazil, in a hypothetical mature oil reservoir through EOR operation. Simulations based on mass, energy and entropy balances, as well as economic analysis, were assessed for the process of CO₂ sequestration combined with EOR. This model takes into account the energy requirements for the whole CO₂ sequestration process, as well as the emissions inherent to the process. Additionally, a breakdown cost methodology is proposed to estimate the main financial determinants of the integrated EOR with CO₂ sequestration (costs of CO₂ purchase, compression, transportation and storage). Project evaluation is derived from a cash flow model, regarding reservoir production profile, price and costs, capital expenditures (CAPEX), operating expenditures (OPEX), carbon credits, depreciation time, fiscal assumptions etc. A sensitivity analysis study is carried out to identify the most critical variables. Project feasibility, as expected, is found to be very sensitive to oil price, oil production, and CAPEX. Moreover, there is the contribution from the mitigation of the greenhouse gas (GHG) by storing a significant amount of CO₂ in the reservoir where it can remain for thousands of years.