毛细管数效应对凝析气井流入动态的影响

凝析油析出是凝析气藏开发中普遍存在的现象, 因而常表现出与干气流入动态不同的特性。理论和现场应用表明, 直接利用干气或折算方法进行凝析气井动态预测会带来较大的误差。其原因是忽略了反凝析液对凝析油气相对渗透率的影响。利用凝析气相态理论和闪蒸计算方法, 考虑流体相态和组分的变化以及凝析气井的表皮系数, 引入稳态理论的两相拟压力函数, 考虑毛细管数效应对凝析油气体系相对渗透率的影响, 建立了拟稳态条件下的凝析气井流入动态预测方法。实例应用表明, 采用考虑毛细管数效应的凝析油气两相拟稳态流入动态方程, 弱化了凝析油的堵塞作用, 有助于正确评估凝析气井的产能, 准确把握凝析气藏的动态特征。     

Experimental Research of Critical Condensate Saturation and Flow Characteristics of Gas Condensate Reservoir

The critical condensate saturation is a key parameter to reflect condensate flow capacity. The authors propose an experimental method to determine the critical condensate saturation and analyze the flow characteristics of gas condensate by coreflooding and chromatography. Using this method, they perform two sets of experiments with real-core of a gas condensate reservoir and a binary mixture fluid of methane and n-pentane under 84°C. Experimental results show that the critical condensate saturation is 3.04% and 4.66% when irreducible water saturation is 40% and 27%, respectively. The results also indicate porous media will raise the dew point pressure. The irreducible water and capillary number effect is conducive to the flow of condensate. Based on experimental researches, the authors theoretically analyze the distribution and mobilization characteristics of condensate. Although critical condensate saturation is low, it doesn't mean the condensate will be able to flow freely when it achieves the value, and condensate saturation will continue to increase. Compositional simulation is performed to demonstrate that the critical condensate saturation is low, which is important for the high effective development of a gas condensate reservoir.     

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.     

凝析气藏考虑毛管数和非达西效应的渗流特征

近期的大量理论和试验研究发现,高速流动导致的毛管数和非达西效应对近井油气相对渗透率有显著影响,仅考虑非达西效应无法准确描述油气真实渗流状态。准确理解并考虑这2种效应的影响对凝析气藏渗流动态分析以及生产动态预测有很重要的意义。建立了油气两相渗流的定解问题,得到了拟稳态形式的流入动态方程。在三区渗流机理上,首次综合考虑了毛管数和非达西效应对相对渗透率的影响。实例分析揭示了高速流动下油气相对渗透率变化及油气分布状态新特征。对不同流入动态模型的对比分析表明,本方法比现有方法更有助于正确预测生产动态,评估气井产能。     

The Effect of Water Vaporization on the Well Productivity of Gas Condensate Reservoirs

Well productivity is a crucial concern in predicting the performance of many gas condensate reservoirs. Accurate forecasting of gas-condensate well productivity usually requires fine-grid simulation to model the formation of the liquid bank and to account for high-velocity phenomena and changes in relative permeability at high capillary numbers. At early stages of production, the pressure drop in the near-wellbore region builds up the molar content of water in gas. This, in turn, results in water vaporization, and hence a drop in the connate water saturation. When water vaporization occurs, pores that were formerly filled by connate water now becomes occupied by gas and condensate only. This causes a change in gas and condensate saturations near the wellbore that can affect the well productivity. No lucid numerical simulation approach considering this effect is suggested in the literature. The authors investigated the effects of water vaporization on the near-wellbore region by compositional simulator of GEM. Enhancement of gas well productivity is observed.     

水力裂缝设计对凝析气藏产能的影响

通过对凝析气藏水力裂缝伤害的机理分析,提出一种计算模型,预测凝析气藏压裂井的产能,量化气体渗透率降低对产能的影响,进而优化凝析气藏水力裂缝设计。这种模型的独特性主要倾向于必要的裂缝长度,目的是弥补凝析液析出产生的伤害。该模型也为准确计算用来优化凝析气井产能的压力降提供了依据。     

考虑毛管数和非达西效应的凝析气液两相流入动态

近期的大量理论和实验研究发现,高速流动导致的毛管数和非达西效应对近井油气相对渗透率有显著影响,而目前仅仅考虑非达西效应无法准确描述油气真实渗流状态。如何准确理解并考虑这两种效应的影响对于凝析气藏渗流动态分析以及生产动态预测有很重要的意义。本文建立了油气两相渗流的定解问题,得到了拟稳态形式的流入动态方程。在三区渗流机理上,首次综合考虑了毛管数和非达西效应对相对渗透率的影响。实例分析揭示了高速流动下油气相对渗透率变化及油气分布状态新特征。对不同流入动态模型的对比分析表明,本文方法较之现有方法更有助于正确预测生产动态,评估气井产能。     

考虑气液两相流的凝析气井生产动态研究

凝析气藏开发中,反凝析液析出常 常不可避免,由此造成储集层渗流表现出与干气或常规溶解气驱流动不同的特性。目前大多采用单相气或折算方法来进行凝析气井的流入动态预测,理论和现场应用表明,这类方法会带来较大的误差,因其忽略了凝析液析出对气相相对渗透率的影响。尽管众多学者对此进行了大量的理论研究,但由于模型过于复杂或是缺乏严格、全面的理论描述,均限制了其应用。以油气两相渗流的基本理论为基础,可以给出拟稳态形式的流入动态方程,同时还可以对储集层参数分布计算进行严格理论证明。实例应用表明,采用提出的油气两相流入动态方程有助于正确评估凝析气井产能,准确把握储集层动态。     

页岩气储层水力压裂物理模拟试验研究

为了给彭水地区页岩气开发提供技术支持,进行了页岩储层水力压裂物理模拟试验研究,建立了一套页岩储层水力压裂大型物理模拟试验方法。利用声发射监测系统实时监测了页岩压裂裂缝的产生与扩展演化过程,观察了水力压裂裂缝形态,并探讨了压裂液黏度、地应力差异系数、压裂液泵注排量等因素对水力裂缝形态及其扩展的影响。试验结果表明,随着压裂液黏度降低、地应力差异系数减小,水力裂缝沿着天然裂缝方向延伸,将原有天然裂缝沟通并形成网络裂缝。根据泵压曲线变化结果,提出在实际压裂施工过程中采用变排量的方式提高压裂改造体积,这可为页岩气压裂优化设计提供依据。      

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。     

Comparison of Simulation Methods in Gas Condensate Reservoirs

Formation of condensate bank around a gas condensate well due to reduction in bottom-hole pressure below its dew point will impose a significant reduction on the well productivity owing to a sharp fall in the gas effective permeability. Hence a better understanding and modeling of this behavior will lead to a more precise prediction of reservoir performance. Therefore the objective of this work was to make a comparison between different simulation methods of gas condensate reservoirs in order to check the validity of them respect to the most accurate one (i.e., fine grid) fully compositional model. This study shows that the modified black oil model would be adequate to simulate depletion cases above and below gas condensate dew point. However, the two phase pseudo-pressure method is not always applicable in simulating gas condensate reservoirs especially in the presence of high velocity flow effects.     

Long-Term Performance of Hydraulically Fractured Layered Rich Gas Condensate Reservoir

Compositional simulator has been used to investigate the effect of hydraulic fracture on the performance of a layered rich gas condensate reservoir in Saudi Arabia. The reservoir consists of five layers having permeabilities ranging from 0.08 to 115 md with about 68% of the gas reserve located in the lowest permeability layer. The fracture is assumed to penetrate all layers. The results of this investigation showed that hydraulic fracturing of such a reservoir is effective in improving the productivity of the gas condensate wells. The productivity index (PI) of the cases investigated was found to increase by as much as 3.6 folds. Hydraulic fractures were also found to delay the onset of the dew point pressure and consequently extend the production plateau above the dew point pressure. The production plateau above the dew point pressure was found to increase with increasing the dimensionless fracture conductivity. The results of this study also showed that once the dew point pressure is reached, the flowing bottom hole pressure was found to drop sharply to the specified minimum flowing bottom hole pressure in the fractured and nonfractured cases. However, the drop is less severe in the fractured case. This sharp drop in the flowing bottom hole pressure results in dropping the productivity of the gas condensate wells. Condensate build up along the fracture faces was found to be more significant in the high permeability layers. At early times after reaching the dew point pressure, the highest condensate saturation was found to be in the highest permeability layer. However, at late times (after reaching pseudo steady state) it decreased to a certain level above the critical condensate saturation. Finally, formation cross-flow is found to improve the productivity of the fractured and the nonfractured gas condensate wells. However, the improvement is more pronounced in the fractured cases.     

Long-Term Performance of Hydraulically Fractured Layered Rich Gas Condensate Reservoir

Abstract

Compositional simulator has been used to investigate the effect of hydraulic fracture on the performance of a layered rich gas condensate reservoir in Saudi Arabia. The reservoir consists of five layers having permeabilities ranging from 0.08 to 115 md with about 68% of the gas reserve located in the lowest permeability layer. The fracture is assumed to penetrate all layers. The results of this investigation showed that hydraulic fracturing of such a reservoir is effective in improving the productivity of the gas condensate wells. The productivity index (PI) of the cases investigated was found to increase by as much as 3.6 folds. Hydraulic fractures were also found to delay the onset of the dew point pressure and consequently extend the production plateau above the dew point pressure. The production plateau above the dew point pressure was found to increase with increasing the dimensionless fracture conductivity. The results of this study also showed that once the dew point pressure is reached, the flowing bottom hole pressure was found to drop sharply to the specified minimum flowing bottom hole pressure in the fractured and nonfractured cases. However, the drop is less severe in the fractured case. This sharp drop in the flowing bottom hole pressure results in dropping the productivity of the gas condensate wells. Condensate build up along the fracture faces was found to be more significant in the high permeability layers. At early times after reaching the dew point pressure, the highest condensate saturation was found to be in the highest permeability layer. However, at late times (after reaching pseudo steady state) it decreased to a certain level above the critical condensate saturation. Finally, formation cross-flow is found to improve the productivity of the fractured and the nonfractured gas condensate wells. However, the improvement is more pronounced in the fractured cases.     

反凝析污染对凝析气井生产动态的影响研究

凝析气藏随着压力、温度等热动力学条件的改变,凝析油气体系的组成及其物性参数也发生变化,发生相间传质和相态变化等物理化学现象,并且存在反凝析现象,降低气相渗透率,减少气井产能。该研究使用Eclipse数值模拟软件中的组分模型,结合新疆某凝析气藏X19井地质及油藏工程资料建立单井模型,研究凝析气井生产过程中凝析油饱和度的分布状况、井底流压变化规律,以及配产气量、渗透率、生产时间等因素对于凝析气井生产动态的影响。     

凝析气平衡冷凝液量计算

根据相平衡理论和闪蒸计算,给出了根据井沆物组分计算不同压力温度条件下的液量的公式和详细的计算步骤,以吐哈油田一口凝析气井为例进行了凝析液量的计算。结果表明,计算结果与实测值接近,方法可行。     

不同注入气对凝析气相态的影响

凝析气藏开发过程中最大的问题是由于地层压力低于露点压力以下而造成凝析油损失,注气是防止凝析油析出并提高采收率的较好方法,但目前不同注入介质对凝析气相态影响还未进行系统研究,以一个真实的凝析气藏为例,使用自行开发的PVTCOG软件和PR状态方程,研究和对比了在凝析气藏定容衰竭不同阶段,注干气、氮气及二氧化碳气对凝析气相态的影响。研究表明不同种类的气体对凝析气露点、凝析油饱和度及采收率有明显不同的影响。     

苏里格气田压裂效果评价方法

为探索适宜的压裂工艺技术并提高整体开发效益,研究了苏里格气田压裂效果的评价方法,建立了压裂效果经济评价的模型。从工艺技术效果和经济的角度综合评价认为,适度规模压裂、CO2压裂、分层压裂应是苏里格气田的主要压裂工艺措施。     

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.     

白庙凝析气藏压裂工艺技术研究与应用

针对白庙气田反凝析严重 ,储层物性差 ,具有低孔、低渗、压裂难度大的特点 ,研究了压裂液和施工参数对气田压裂效果影响。通过优选适合该地区的低伤害压裂液 ,减少液体对储层的伤害 ;采用压前进行小型压裂测试 ,提高压裂设计参数的准确性 ;应用复合压裂工艺技术、前置液中加入支撑剂段塞及裂缝强制闭合技术 ,在施工过程中采用分段破胶和保护地层 ,以及撬装制氮气举排液等技术 ,大大提高了白庙气田的施工成功率和压裂效果。     

凝析气井超完全覆盖射孔效果评价方法探讨

对于天然气和凝析油同产井,评价超完全覆盖射孔效果影响因素增多,加大了评价难度.在分析影响产能评价因素的基础上,提出新的技术途径消除这些影响,用该方法求出的评价指标能精确地评价射孔效果,且操作简便,易于掌握.