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鄂尔多斯盆地苏里格气田是我国陆上发现的较大气田之一 ,目前对该气田分析的 5口气井的气油比为 15 .9× 10 4～ 98.9× 10 4m3 /m3 ,是个湿气田或干气田 ,然而初步的实验研究结论恰恰相反 ,该气田确是一个凝析气田。气藏类型经验判断表明 ,该气田可能是“常规干气田” ,也可能是“无油环凝析气田” ,处于干气藏和凝析气藏的过度带 ,没有统一的结论。相态实验研究表明 ,该气田为特低含凝析油的凝析气田。实验还发现 ,退泵降压观测到的露点压力与进泵升压观测到的雾和油花消失的压力不相同 ,后者大于前者 ,而且相差很大 ,说明该气田凝析油一旦析出 ,就较难气化。气油比改变露点压力也相应改变 ,气油比升高 ,露点压力降低 ,说明高气油比井的气含量大、油含量少 ,使油完全溶解在气中的压力就低。定容衰竭预测结果表明 ,该气田的反凝析油量很低 ,但是如果气井在井底压力低于露点压力下经过长时间生产 ,井底周围地层中仍然会有凝析油聚集 ,造成反凝析油动态污染     

毛细管压力对凝析气相态的影响

凝析油气体系和储层多孔介质是一个相互作用的系统,考虑多孔介质界面现象对凝析气相态规律和渗流规律的影响,能更真实地反映凝析气在储层多孔介质中的相态特征和渗流特征,特别是低渗透凝析气藏,更不能忽略毛细管压力对凝析气相态的影响。建立了考虑毛管力的凝析气相态计算模型,利用SPE 21428的流体组成研究了毛管力对凝析气露点及反凝析进程的影响。研究认为,毛管力和界面张力决定毛管力对凝析气相态影响的强弱,当孔隙半径达到10-8m数量级时,毛管力对凝析气露点及反凝析进程的影响十分显著。     

Experimental study into the effectiveness of the partial gas cycling process in the gas-condensate reservoir development

In this study a laboratory study was carried out with the purposes of estimating the effectiveness of the gas cycling process during gas-condensate reservoir development. Specific laboratory equipment was constructed to carry out an experimental investigation by modelling the gas injection and reservoir depletion process. Volumetric properties, fog up, liquid drop-out condition, and retrograde dew point pressures of gas-condensate fluids were investigated. The reservoir fluid was recombined based on samples from Azerbaijan natural gas-condensate reservoir. Results are describing gas injection effect on condensate/gas ratio and condensate recovery in each pressure step. These have provided an understanding on the influence of the retrograde dew point pressure on optimum gas injection stage. The analyses also assure that as condensate/gas ratio decreases continually during the gas injection process, which causes the reservoir fluid PVT characteristics to be changed accordingly furthermore the reservoir pressure can be depleted in order to vaporize the liquid phase and to maintain the reservoir fluid to be in a single phase state during the reservoir exploitation. It was seen to be closely related with retrograde dew point pressure and fog up pressures. Therefore, in terms of incorporating colloidal systems into the subject focusing more on the region between fogging up and retrograde condensation gave interesting results.     

含水凝析气相态特征及非平衡压降过程产液特征

气态水的存在对凝析气藏相态特征的影响不容忽视,常规的相态测试过程无法模拟含水凝析气田开发过程中近井带的非平衡压降过程的实际产液特征。利用PVT筒开展了含气态水凝析油气体系相态特征实验,研究了气态水对凝析气相态特征的影响,并通过缩短凝析气体系定容衰竭过程的平衡时间,模拟含水凝析气田开发过程近井带的非平衡压降衰竭过程,对比分析了非平衡压降过程含水凝析气体系中凝析油、水的抽提蒸发效应。结果表明,气态水的存在引起了凝析油气体系中重质含量的增加,导致露点压力升高,反凝析提前,最大反凝析压力提高,反凝析液量增加。含水凝析油气体系在非平衡压降衰竭过程中,由于气液相体系未达平衡,导致液相滞后析出并随气相运动一起被采出,造成凝析油采出程度和产水量提高,且非平衡压降速度越大,凝析油采出程度越高。因此,凝析气田近井带的非平衡压降有利于凝析油的开采并缓解液锁的发生。     

A condensation model for calculating pressure gradients in condensate wells

A method is presented to calculate pressure traverses in a condensate well utilizing existing techniques for two-phase flow of fluids in pipes. Existing correlations have been developed for black oil flow where gas evolves from the oil as pressure and temperature are reduced. In the case of condensate flow, a liquid evolves as pressure and temperature are reduced, thereby making the existing correlations inapplicable. The Peng-Robinson equation of state is used to model the gas/condensate fluid and predict the gas/liquid ratio at any pressure and temperature as a traverse is calculated for the depth of the flowing well. The existing two-phase flow correlations for black oil flow are used in this work to predict gas/liquid properties such as liquid holdup, friction factors, and flow regimes. This model is then applied to several wells for which extensive data was taken, including PVT properties and pressure measurements.     

Investigating the Effect of Capillary Number on Performance Prediction of an Iranian Fractured Gas Condensate Reservoir

Abstract

Gas condensate reservoirs are one of the most complicated reservoirs in which the special thermodynamic behavior of reservoir fluid leads to condensate buildup instead of gas expansion, when the reservoir pressure drops below dew point pressure. To justify the phase behavior of such reservoirs, several models have been proposed. One of the models is a capillary number model that has a considerable effect on the shape of relative permeability curves. Taking account of capillary number is shown to improve the performance prediction of gas condensate reservoirs that otherwise is poorly predicted. In pressures below dew point pressure, velocity and surface tension between gas and oil increases more rapidly in the vicinity of the well compared with other parts of the reservoir, which results in condensate saturation reduction and gas relative permeability improvement. The authors model a fractured gas condensate reservoir with and without taking capillary number into consideration; the performance prediction results are compared to the actual results. The model with capillary number included is shown to be able to predict the performance with a greater accuracy than the case without capillary number.     

The solubility of gas components and its importance in gas-condensate reservoir development

The authors investigated the solubility of the gas components in the natural gas-condensate systems and its importance in gas-condensate reservoir development. Also, they discuss some fundamental aspects of preferable methods for recovering trapped retrograde condensate in the formation that is left after primary production. Based on the obtained results from the constant composition expansion test of seven different gas-condensate systems provided a greater understanding of the occurrences and interchanges between liquid and gas phases in the recombined reservoir fluids. The correlation between amount of the dissolved gas in the liquid phase, the volume of vaporized condensate in the gas phase and retrograde condensation pressure was investigated. Analysis of this data identified that increasing dissolved gas in the liquid phase, increases vaporized condensate even in the same thermobaric condition and decreases the retrograde condensation pressure of the gas-condensate systems. It was determined that the solubility of gas components in the fluid should be considered when projecting the gas-condensate reservoirs development. As, improving the solubility of gas components in the condensate decreases the system fog up and retrograde condensation pressures and improves stability of aerosol condition of gas-condensate fluid, it influences on the reservoir condensate bearing to be increased. Therefore, injected gas for gas cycling or revaporization of accumulated condensate from the core can be controlled for the purpose of increasing its solubility and condensate bearing capability.     

凝析气藏压力恢复试井分析的新认识

低于露点压力的凝析气藏的压力恢复曲线特征不同于高于露点压力的凝析气藏，文中根据三区域径向复合模型，将低于露点压力的凝析气藏压力恢复曲线的上翘解释为地层流体凝析饱和度的变化，内区为低凝析饱和度区，外区为原始流体凝析饱和度区，中间过渡带为高凝析饱和度区，而非传统的储层物性变化或部分渗透断层的影响，并结合矿场实例，说明其适用性。     

水驱凝析气藏地层压力计算方法

凝析气藏地层压力是计算气藏储量、评价气井产能、进行动态分析及反凝析评价等必不可少的重要参数。水驱凝析气藏的开发是气藏开发中最复杂的类型之一,在开发过程中,地层压力不断下降,凝析油析出,凝析气中水蒸汽含量增多,边、底水不断侵入,准确计算及预测地层压力就显得尤为困难及重要。通过计算考虑多孔介质吸附及毛管力影响的反凝析油,实验测试不同压力下凝析气中水蒸汽含量,根据物质平衡原理,建立了考虑多孔介质吸附、毛管力及水蒸汽影响的水驱凝析气藏物质平衡新方程,并迭代求解得到任意生产时刻地层压力。应用结果表明,考虑多孔介质吸附、毛管力及水蒸汽影响计算的地层压力,更接近实测地层压力,从而减轻了现场测试工作量。     

低渗凝析气藏气井产能的正确预测

地下多孔介质因具有较大的比面积而对凝析油气流体具有较强的吸附能力，多孔介质吸附对凝析油气渗流过程的影响是国内外较为关注的问题。文章在新的凝析油气渗流微分方程的基础上，通过渗流数学模型的建立与求解，建立了考虑相态变化与多孔介质吸附影响的凝析气井产能方程，探讨了凝析气井产能正确预测的方法。通过实例计算和分析，结果表明：考虑与不考虑多孔介质吸附影响的凝析气井产能存在较大的差别，凝析气井地层压力低于露点压力后，将出现反凝析液损失，将引起气井产能较快地降低，验证说明了在对凝析气井进行试井解释时可考虑采用复合气藏模型。     

凝析气藏近井地层油气产状及渗流特征

提出了孔隙介质条件下凝析油气相态特征预测的相平衡模拟方法。将该方法应用于牙哈等凝析气藏的露点、反凝析油饱和度等相态特征研究,取得了令人满意的结果。将孔隙介质条件下凝析油气体系相平衡计算方法引入凝析油气渗流理论,得到了考虑吸附和毛管凝聚作用影响的凝析油气体系物化渗流模型,给出了考虑界面现象影响的凝析气井产能方程及描述凝析气藏近井地层反凝析油饱和度分布规律、气相相对渗透率分布规律、压降漏斗分布规律的数学模型。通过牙哈凝析气藏气井产能、反凝析油饱和度分布规律以及气相相对渗透率分布规律的预测计算,表明多孔介质界面现象的作用会加剧地层反凝析现象,产生附加的反凝析动态地层伤害,引起凝析气井气相相对渗透率和产能降低。     

The Effect of Nitrogen Injection on Production Improvement in an Iranian Rich Gas Condensate Reservoir

In gas condensate reservoirs, after a decrease in pressure below the dew point pressure, condensate formation would occur. One of the common and practical methods for prohibiting the rapid pressure drop in the reservoir and reduction of liquid dropout is gas injection. In this study, experimental measurement, the full field reservoir model and an economical evaluation have been performed to investigate the effect of nitrogen injection on an Iranian Southwestern gas condensate reservoir. At first, swelling and CVD tests were carried out to determine the swelling factor and changing the saturation pressure by nitrogen. Then, the full field simulation (history matching and prediction) was performed and finally an economical evaluation has been made. The results show that injecting more volumes of nitrogen cause to decrease the liquid dropout, increase the dew point pressure, and condensate ultimate recovery, but this process is not an economical project.     

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目前在研究凝析气的渗流和相态问题时，当地层压力降低到露点压力之后，采用的都是等温瞬时平衡的概念，而在凝析气井生产过程中，当近井带压力降至体系露点压力以下后，采用的都是等温瞬时平衡的概念，而在凝析气井生产过程中，当近井带压力降至体系露点以下，由于气相的高速流动，气液相并不充分接触，液相析出后运动滞后而逐渐沉积，部分液相组分会因高速气流夹带而呈气相运动一段距离后才变成液相析出，也就是说液相析出量的多少要受到平衡时间的影响。章从体系的强度性质出发，引往平衡时间因素建立非瞬时平衡相态描述方法。利用LHSS方程研究了凝析气井近井地带高速流动区在非瞬时相平衡条件下凝析液的析出和温降。结果表明，由于非瞬时平衡作用导致高速流动区液相析出量减少，近井带的凝析油动态饱和度比用瞬时平衡预测的低。     

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在油气藏中,油气流体和储层多孔介质是一个相互作用的系统,油气体系相平衡计算应考虑多孔介质中的界面现象的影响。文章从热力学基本理论出发,建立了考虑毛细管压力的相平衡计算模型。为了论证毛细管压力对油气体系相平衡的影响程度,针对我国两个凝析气藏,分别对油气体系的毛细管压力,露点压力,反凝析液量和p-T相图形态进行了相诚模拟计算。并利用热力学亚稳态和新相生成理论中的开尔文（Kelvin)方程对其相态模拟计算结果作出了满意的解释。     

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对凝析气井在高温高压下取其储层流体称之为ＰＶＴ取样,其目的是通过在室内分析该流体,得到表述储层流体物理和化学性质的参数。在现场中通常不采用井下取样,原因是：井下温度、压力高,作业困难;井筒中自上而下的温度和压力变化,导致凝析油析出,使油气比随井筒变化且规律难循;地面取样安全可靠、施工方便。对如何在地面取ＰＶＴ样作了全面和详细的介绍,包括：取样井的选择;取样前的设备选择;各类取样井的产量调整;取气样的工艺技术要求和注意事项;取液样的工艺技术要求和注意事项;分离器样品的质量检验等。该技术在对塔里木盆地凝析气井地面ＰＶＴ取样时得到广泛的应用,通过ＰＶＴ样品的室内分析,获得油气的摩尔组分、双相偏差系数、流体变化规律、露点压力、压力和体积关系、反凝析液量、反凝析压力、全相图分析等数据与资料,为优化开采方式和制定增产措施,提高油气采收率提供了理论依据。     

Mathematical Model For Bubbly Water-Heavy Oil-Gas Flow in Vertical Pipes

Abstract

In this work a unidimensional, time-dependent homogeneous mathematical model is presented. The model is able to predict pressure, temperature and velocity profiles of the flow known as bubbly-gas—bubbly-oil, which can be present when water-heavy oil and gas flow simultaneously in vertical pipes. The mathematical model consists of mass, momentum, and energy conservation equations and its numerical solution is based on the finite difference technique in the implicit scheme. The thermodynamic and transport properties of the fluids are estimated by correlations reported in the literature. The effects of different water-gas and water-oil shear stress correlations on the prediction were evaluated. As a result, some correlations are recommended to simulate the bubbly-gas—bubbly-oil flow. A new correlation for water-heavy oil-gas friction factor is suggested. A comparison of the model with existing experimental data shows a satisfactory agreement.     

低渗透凝析气藏的反凝析特征

深层低渗透凝析气藏的数量越来越多，了解其反凝析特征是气藏开发正确决策的重要基础。为此，以某油田的深层低渗透凝析气藏为主要研究对象，通过CVD测试及真实岩心衰竭实验测试，研究了深层低渗透凝析气藏的反凝析特征。研究结果表明：①PVT筒的定容衰竭与多孔介质中的衰竭特征有较大的差异，因此应尽可能采用岩心衰竭实验研究深层低渗透凝析气藏的真实反凝析相态特征；②该油田深层低渗透凝析气藏衰竭开发过程中反凝析呈中等偏低水平，近井地层的反凝析液堆积速度较慢，最大反凝析液饱和度值对应的地层压力与气藏标定的废弃压力接近，表明该油田深层低渗透凝析气藏比较适合于采用衰竭方式开发；③该油田深层低渗透凝析气藏衰竭开发过程中产生的凝析油饱和度小于临界流动饱和度，析出的凝析油不会产生反蒸发，因此在气藏开发过程中防止反凝析污染就显得非常重要。     

An Experimental Phase Diagram of a Gas Condensate Reservoir

Abstract

Most condensate gas reservoirs discovered in Iran are rich in intermediate components. The phase diagram of these fluids is essential for reservoir management. The available commercial reservoir fluid simulators are not able to find the critical point of some of these condensate gas reservoirs to obtain the phase diagram quality lines. The quality lines of these reservoir's samples can be obtained experimentally using the constant mass expansion test data. The authors present experimental development of gas condensate phase diagram along with retrograde condensation and revaporization characterization during the reservoir depletion process of one Iranian condensate gas reservoir.     

牙哈凝析气藏二次注气抑制反凝析机理及相态特征

为解决凝析气藏天然气回注率不足,地层压力低于露点压力而出现的反凝析损失等问题,以塔里木盆地牙哈凝析气藏反凝析损失监测井地层流体取样器(MDT)取样为基础,运用高温高压PVT相态实验测试和模拟技术,建立了牙哈凝析气藏二次循环注气抑制反凝析损失机理的相态特征研究方法,对提高牙哈凝析气藏凝析油采出程度的可行性和有效性做出了评价。通过目前地层压力下反凝析油和剩余凝析气体系的实验室再现,分别测定了其色谱组成、相态特征和p-丁相态图;分别针对反凝析油和地层剩余凝析气,开展了注气增溶膨胀实验、多次接触抽提实验和注气抽提实验,对地层剩余平衡凝析气还开展了加注干气传质扩散过程非平衡相态行为实验;分析了二次循环注气抑制反凝析损失、降低其反凝析油饱和度、使凝析油产生相态反转的相行为机理;给出了二次循环注气开发时应尽量使其注气压力高于露点压力的建议,当注入0.82 PV时,凝析油累积采出程度将提高13.55%。该研究成果为牙哈凝析气藏的增产提供了重要技术支撑。     

凝析气井井筒压力计算

准确计算凝析气井井底压力是正确预测产能、合理制订生产方案的关键,近年来凝析气井压力计算重点考虑黑油模型和组分模型的差异,而对优选气液两相管流压降模型的重要性却认识不足。为此,采用Govier-Fogarasi公开发表的94口凝析气井实验数据对工程常用的无滑脱模型、HagedornBrown、Orkiszewski、Gray、MukherjeeBrill、HasanKabir分别按黑油模型和组分模型预测井筒压力。井底流压和压降梯度统计评价结果表明:两相流模型的选择对凝析气井井筒压力预测结果影响较大,而组分模型和黑油模型对部分两相流模型在一定条件下对凝析气井井筒压力计算产生影响;推荐使用Gray模型+黑油模型和HagedornBrown模型+组分模型来预测凝析气井压力剖面,并给出了无滑脱模型的适用条件(液气比为0.5~5m3/104 m3、产气量大于5×104 m3/d);最后指出,采用组分数据计算凝析气井压力剖面时,其数据选择尤为重要,否则预测的误差会增大。该研究成果对于凝析气藏的高效开采具有重要的意义。