扩散对凝析气藏相变与渗流机理的影响研究

发布时间：2018-05-18 06:27

本文选题：凝析气藏 + 传质扩散　；参考：《西南石油大学》2017年硕士论文

【摘要】：凝析气藏作为一种特殊的复杂气藏,在石油与天然气勘探开发以及国家能源战略储备中占有重要的地位。其特殊的复杂性主要表现为凝析气在露点压力以下时会发生反凝析现象,析出的凝析油与凝析气在气液界面处发生分子扩散现象,油、气的相态也会随之发生转变,导致储层内油气饱和度的变化,从而影响体系渗流的特性。由于体系达到新的平衡需要一定的平衡时间,所以这一转变过程是非瞬时平衡的。本文研究受国家自然科学基金项目(51374179)资助;首先配制两种流体样品(含水/不含水)开展平衡态与非平衡态条件下的高压物性测试实验,分析了气态水和非平衡效应对体系相态的影响;利用现场获取的实际储层岩心开展不同衰竭速度的模拟实验,分析衰竭速度对凝析气藏开采效果的影响;在双膜理论的基础之上,建立了考虑扩散影响的凝析气非平衡相态计算模型,以及一维多组分渗流数学模型。通过系统研究,得到如下重要结论及认识。(1)气态水类似重烃的性质,凝析气—气态水之间发生传质现象,造成凝析气中轻组分损失而重组分的含量增加。气态水的存在加快了体系的反凝析和反蒸发速度,导致凝析气体系膨胀能力增强及露点压力上升,并且气油比和反凝析液饱和度均增加。(2)恒组成膨胀实验研究表明,衰竭速度越大,体系偏离平衡态就越严重,非平衡效应越严重,析出反凝析液饱和度更低。(3)岩心衰竭实验表明,随衰竭速度增大,析出凝析油重组分含量及凝析油采收率逐渐增大;衰竭至最大凝析压力之前,体系以反凝析为主,凝析油采出程度增长幅度较大,气油比缓慢升高;在最大反凝析压力以后,体系以反蒸发为主,气油比出现陡升,凝析油采出程度增长速度变缓。(4)非平衡相变模型计算结果表明,非平衡效应会降低反凝析液的析出,随着非平衡态压降速度的增加,体系偏离平衡态的程度越大,反凝析液的饱和度越小,"非平衡"现象越明显。同时,在整个降压的过程中,气相向液相的传质通量大于液相向气相的传质通量,且随着C原子数的增加,净传质通量越来越小,表现为反凝析现象强于反蒸发现象。体系中各组分的净传质通量随着压力的降低而逐渐减小,压降速度越大,各组分的净传质量越大。(5)非平衡渗流模型计算结果表明,受分子扩散传质的影响,衰竭速度越快,凝析气中重质组分含量增大,而凝析油中轻质组分含量增加;非平衡效应使凝析液析出滞后随气相一同被采出。受扩散和非平衡效应的综合影响,地层中析出凝析油饱和度均低于平衡态计算值。凝析油采收率受衰竭速度、束缚水饱和度、储层物性的影响较大,但是干气采收率受影响程度较小。
[Abstract]:As a special complex gas reservoir, condensate gas reservoir plays an important role in oil and gas exploration and development as well as national energy strategic reserve. Its special complexity mainly shows that the condensate gas will occur reverse condensate phenomenon when the dew point pressure is lower, the condensate oil and the condensate gas will have the molecular diffusion phenomenon at the gas-liquid interface, and the phase state of oil and gas will also change with it. The change of oil and gas saturation in the reservoir will affect the percolation characteristics of the system. Since it takes a certain time for the system to reach the new equilibrium, the transition process is non-instantaneous equilibrium. In this paper, funded by the National Natural Science Foundation of China 51374179, two kinds of fluid samples (water / no water) are prepared to test the physical properties of high pressure under the condition of equilibrium state and non-equilibrium state. The effects of gaseous water and non-equilibrium effects on the phase behavior of the condensate gas reservoir are analyzed, and the effects of failure velocity on the recovery of condensate gas reservoirs are analyzed by using the actual reservoir cores obtained in the field to carry out simulation experiments of different failure rates. Based on the two-film theory, a model for calculating the non-equilibrium phase behavior of condensate gas considering the effect of diffusion and a mathematical model for one-dimensional multicomponent percolation are established. Through systematic study, the following important conclusions and cognition. 1) the properties of gaseous water are similar to heavy hydrocarbons. Mass transfer occurs between condensate gas and gaseous water, which results in the loss of light component and the increase of recombination fraction in condensate gas. The existence of gaseous water accelerates the rate of reverse condensation and reverse evaporation, which leads to the enhancement of the expansion ability and the increase of dew point pressure of the condensate gas system, and the gas / oil ratio and reverse condensate saturation increase by the constant composition expansion experiment. The larger the failure rate, the more serious the system deviates from the equilibrium state, the more serious the non-equilibrium effect is, and the lower the saturation of precipitated reverse condensate is. The recombination content of condensate oil and the recovery factor of condensate oil gradually increased. Before the maximum condensate pressure, the system was mainly reverse condensate, the recovery degree of condensate oil increased greatly, the ratio of gas to oil increased slowly, and after the maximum reverse condensate pressure, The calculation results of non-equilibrium phase transformation model show that the non-equilibrium effect will decrease the precipitation of reverse condensate, and the pressure drop rate of non-equilibrium state will increase with the increase of pressure drop rate in non-equilibrium state. The more the system deviates from the equilibrium state, the smaller the saturation of the reverse condensate solution is, and the more obvious the "non-equilibrium" phenomenon is. At the same time, the mass transfer flux from the gas phase to the liquid phase is larger than that from the liquid phase to the gas phase during the whole depressurization process, and with the increase of the number of C atoms, the net mass transfer flux becomes smaller and smaller, showing that the reverse condensation phenomenon is stronger than the reverse evaporation phenomenon. The net mass transfer flux of each component decreases gradually with the decrease of pressure, and the larger the pressure drop rate, the larger the net mass transfer mass of each component. 5) the calculation results of non-equilibrium seepage model show that, under the influence of molecular diffusion mass transfer, the failure rate is faster. The content of heavy component in condensate gas increases, while the content of light component in condensate oil increases, and the precipitation lag of condensate is produced with gas phase due to non-equilibrium effect. Due to the influence of diffusion and non-equilibrium effect, the saturation of condensate oil in formation is lower than the calculated value of equilibrium state. Condensate oil recovery is greatly affected by depletion rate, irreducible water saturation and reservoir physical properties, but the dry gas recovery is less affected.
【学位授予单位】：西南石油大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TE312

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