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。     

深层低渗变形介质凝析气藏流体相态研究

以中原油田的深层低渗变形介质凝析气藏为研究对象,采用实验测试和理论研究相结合的方法,研究了气态地层水、界面效应和储层变形作用综合影响下气藏流体的真实相态特征.研究结果表明,气态地层水、界面效应和储层变形作用将导致深层低渗凝析气藏中流体露点压力升高,反凝析过程提前,反凝析油饱和度增加,反凝析污染加重.研究结果对合理编制气田开发方案,提高气田开发水平具有指导意义.     

变形介质中毛细管压力对凝析气藏相态的影响

低渗凝析气藏在开采过程中,随着地层压力的降低,储集层会发生变形,孔隙半径会随有效应力的增大而减小,毛细管压力效应会随孔隙半径的改变而发生变化.为研究毛细管压力对凝析气藏相态的影响,定量分析了储集层变形对平均孔隙半径的影响,建立了同时考虑储集层变形和毛细管压力影响的相平衡数学模型,模拟了一个凝析气藏露点和等组成膨胀过程的相态特征,研究结果表明,变形介质中毛细管压力对凝析油气相态特征的影响比无变形多孔介质中的影响更强,应当考虑变形介质中毛细管压力对液相压力、反凝析液饱和度、液相摩尔含量等产生的影响（对液相压力的影响尤为明显）.在相态特征分析和组成分析的基础上,剖析了毛细管压力对凝析油气相平衡过程的作用机理.     

变形介质中毛细凝聚对凝析气藏露点的影响研究

在凝析油气储层中，毛细凝聚作用会影响凝析气的露点，孔隙越细小，毛细凝聚作用越强。低渗凝析气藏在开采过程中，储层要发生变形，平均孔隙半径会随有效应力的增大而减小，毛细凝聚作用会增强。对此，首先建立了平均孔隙半径随有效应力变化的动态模型；接着基于常规相平衡理论和Kelvin方程，建立了同时考虑毛细凝聚和介质变形的露点压力预测模型；最后作了实例分析，得出了相应的结论：变形介质中毛细凝聚作用对露点的影响比在无变形的介质中强，对低渗透变形介质而言，毛细凝聚作用对上露点压力的影响很小，可忽略不计，而对下露点压力的影响较显著，应当考虑。     

毛细管压力对凝析气体系相平衡的影响

当凝析气藏的地层压力低于露点压力以后,凝析油会因为反凝析现象从气相析出,储层中同时存在气、液、固（指岩石）三相,对于气,液两相流体的气－液界面,由于界面张力的存在,将会产生一个曲面附加压力（称之为毛细管压力）,在多孔介质中,由于孔隙半径小,因而毛细管压力应予以考虑,本文在建立了考虑毛细管压力的相平衡计算模型之后,针对一个实际凝析气藏,分别对其油气体系的毛细管压力,露点压力和恒组成膨胀过程中反凝析液量进行了相态模拟计算,并得出相应的结论。     

地层水对凝析气藏注CO_2相态的影响

常规的凝析气藏衰竭开发和注CO_2开发研究中均忽略了地层水的影响,这与真实情况存在偏差,有可能导致研究结果的不确定性加大。为此,基于CO_2—烃—水相平衡热力学模型,以一个实际近临界凝析气藏为例,通过相态模拟研究了地层水存在对凝析气藏反凝析相态特征和注CO_2相态的影响规律;计算了考虑地层水存在的凝析气定容衰竭反凝析液饱和度和剩余流体组成,以及注CO_2过程中凝析油气相体积分数和CO_2在凝析油气相中体积分数的变化规律。结果表明:1考虑地层水时定容衰竭的反凝析油饱和度更大,剩余流体重组分含量更高;2近临界凝析气藏压力衰竭过程中,由凝析气转变为挥发油的相变发生得更早;3在注CO_2过程中,地层水的存在使得CO_2对凝析油的反蒸发作用降低;4考虑地层水存在时凝析油相体积分数高约14%,CO_2在凝析油中溶解量比不考虑地层水大6%,CO_2含量高和压力较高时差异更明显,同时,地层水的存在也增强了CO_2的溶解封存能力。该研究成果对凝析气藏注CO_2提高采收率和温室气体CO_2埋存评价具有指导意义。     

高含水致密凝析气藏特殊相态变化

高含水致密凝析气藏具有储层低孔、致密、含水饱和度高的特征,在其开发过程中,当压力降低至露点压力以下,流体会发生复杂的相态变化,析出凝析油,形成油、气、水三相渗流,导致渗流阻力进一步增大。与常规凝析气藏相比,高含水致密凝析气藏开发过程中相态变化具有特殊性:(1)储层含水饱和度较高,水相会影响流体的相态变化;(2)由于储层致密、流体复杂,井底附近渗流阻力较大,压降漏斗陡峭,流体相态表现出强非平衡相态变化特征,这与常规凝析气藏平衡相变特征存在明显差异。基于室内PVT筒实验、长岩心驱替实验及非平衡相态理论,系统研究了高含水致密凝析气藏的相态变化特殊规律。研究结果表明:(1)水相会降低凝析气藏的露点压力,增大反凝析油饱和度;(2)凝析气藏存在"凝析滞后"现象,非平衡相变效应可降低凝析油饱和度;(3)针对受地层水影响较小的气井可增大生产压差采出更多的凝析油。针对特殊相变特征,研究结果可以为高含水致密凝析气藏开发过程中制定合理的生产压差提供依据。     

凝析油蒸发动态特征

凝析气藏开采到压力降到露点压力以后，会在储集层中产生液态凝析油，凝析油饱和度常小于临界凝析油饱和度，凝析油黏度大会产生流度差异效应，往往导致凝析油滞留在储集层中。由于相平衡效应，会产生3种不同的凝析油蒸发动态情形：①压力低于最大反凝析压力后的凝析油蒸发效应；②保持压力过程中的凝析油再蒸发效应；③注入流体使地层压力上升过程中的凝析油反蒸发效应。在降压开采过程中，液态凝析油体积逐渐减小，这主要是由于整个压力衰竭过程中平衡气相的中间组分和重组分含量越来越少，为了达到相态平衡，液相中的相应组分重新分配到气相中，从而出现凝析油的蒸发现象。富凝析气藏常常采用注气开发，注入气体与原始凝析气藏流体进行组分交换，使凝析油在地下蒸发现象明显，注入干气不仅能蒸发凝析油中的中间烃类，而且也能蒸发C20 以上的重烃。实际凝析气藏在高注采比条件下，产出凝析油中较重组分含量增加幅度较大，说明当凝析油析出后，通过注气提高地层压力，可以将反凝析的重组分部分反蒸发而采出。图2表1参10     

低渗透多孔介质对高含凝析油型凝析气相态影响

低渗透气藏在我国已发现的气藏中所占比例较大;由于低渗透多孔介质的影响,与常规高渗气藏相比,开发难度较大,尤其是对于凝析气藏.因此,考虑低渗透多孔介质对凝析气体系的影响对于提高我国低渗透凝析气藏开发水平有一定实际意义.此次研究主要分析低渗透多孔介质对凝析气体系相态特征影响.采用中原桥白气藏实际低渗透储层岩心和配置的高舍凝析油型(凝析油含量364 g/m3)凝析气样分别从实验、数值模拟角度研究衰竭过程中,多孔介质、初始水饱和度对凝析油饱和度和残余油饱和度的影响,以及多孔介质对凝析气露点压力影响.研究表明:多孔介质中测试的凝析气露点压力高于PVT仪中测试值;对同一块岩心,采用相同的凝析气样品,随着初始含水饱和度的增加,测得的衰竭至大气压下凝析油残余饱和度越小;衰竭过程中,多孔介质中凝析油流动及再蒸发较PVT仪中明显,凝析油残余饱和度低于PVT仪测试值.对于低含凝析油型凝析气,由于致密储层对凝析油的吸附作用明显,岩心测试的残余油饱和度值高于PVT仪测试值,因此,对于这类凝析气藏必须考虑凝析油污染问题.     

深层低渗透凝析气藏衰竭开发特征模拟研究

以埋藏深度大、储层低渗致密的桥口复杂断块凝析气藏为目标，开展了地层流体相态全分析和衰竭式开发特征仿真模拟实验，研究了气藏衰竭过程中地层反凝析液饱和度分布、采出井流物组成变化、井流物采出程度、一级分离器凝析油和天然气累积采出量、采出气中重质组分含量变化等相态开采指标，为气藏衰竭式开发效果的物质平衡概念评价提供依据。     

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.     

凝析气田N2吞吐解除近井污染可行性研究——以QDX井为例

凝析气藏开发过程中,地层压力降低到露点压力以后,不可避免发生反凝析现象。凝析液在井筒附近聚集,增加地层中液相的饱和度,降低气相渗透率,造成反凝析污染,导致气井产能降低。为了有效解除近井地带反凝析污染,提高单井产能,模拟N2吞吐作业下气井的产能敏感因素,分析评价了减轻反凝析污染的可行性。在QDX井开展了N2吞吐试验,结果表明:实施N2吞吐后,气井油气产量上升,增产效果明显。     

��׽���ëϸ���۶���������¶���Ӱ���о�

凝析气藏流体处于地下多孔介质中,由于多孔介质孔隙壁面的影响,毛细凝聚现象必然存在,从而不可避免地会对反凝析过程产生影响,以致影响凝析气藏的露点。为此,文章在分析毛细凝聚对凝析气藏露点影响机理的基础上,结合流体相平衡的基本理论,建立了考虑多孔介质毛细凝聚影响的凝析油气体系露点预测的相平衡计算数学模型,并结合实例计算分析研究了储层孔隙半径、润湿性等对露点的影响程度。结果表明,亲油岩石毛细凝聚使露点上升,憎油岩石毛细凝聚使露点下降;当润湿性相同时,毛管半径越小,露点所受影响的程度越大;当孔隙半径大于5×10     

A New Method to Predict Water Breakthrough Time in an Edge Water Condensate Gas Reservoir Considering Retrograde Condensation

During the development of gas condensate reservoirs, condensate oil is separated as reservoir pressure drops to the dew point pressure. The prediction for water breakthrough time, the impact of precipitation of condensate oil, is usually ignored, which results in significant difference between prediction and realistic results. In order to better develop edge water condensate gas reservoirs and accurately predict the water breakthrough time, impact from condensate oil should be considered. Therefore, a new prediction formula of water breakthrough time is derived based on fluid flow in porous media considering impact of anti-condensate. A case study demonstrates that it is necessary to consider impact of condensate oil when predicting water breakthrough time. The new predicting formula provides theoretical basis for further research on edge water displacement mechanism as well as significant guidance for management of edge water gas condensate reservoirs.     

The Effect of Hydraulic Fracturing on the Performance of Gas Condensate Systems

Gas condensate reservoirs usually exhibit complex flow behaviors due to the buildup of condensate bank around the wellbore when the bottom-hole pressure falls below the dew point. Hydraulic fracturing improves well productivity by delaying the onset of dew point pressure and also reducing the condensate saturation near the wellbore area. The authors present the results of a study that compared the near wellbore behaviors and productivities of a vertical nonfractured well and a vertical hydraulically fractured well in a low permeability lean gas condensate reservoir. Results show that there is no indication of capillary number effects in this low permeability reservoir because of low production rates.     

CO2压裂后近缝带烃类的相态特征

CO₂压裂与常规水力压裂相比，除具有滤失小、易返排、低伤害等常规优点外，还能降低烃类的露点压力，对易凝析的中间组分产生很强的抽提作用，有效解除了由于温度压力的变化所造成的近缝带凝析油污染。这为提高凝析气藏采收率、制定合理有效的开发手段提供了新的途径。以中原油田白庙凝析气田为例，建立了数值计算模型，研究了CO₂压裂停泵时刻其CO₂量不同时的凝析气藏近缝带烃类的相态变化及各点凝析油饱和度的变化情况。研究结果表明：CO₂气体对凝析气藏烃类的相态影响是CO₂压裂优于常规水力压裂的重要原因，且CO₂量不同时对烃类相态的影响程度存在显著差异。这为现场实际结果的解释及优化凝析气藏CO₂压裂的气体用量和压裂规模提供了理论依据。     

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.