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.     

基于流固耦合的变质岩潜山裂缝型凝析气藏数值模拟研究

BZ气田为渤海最大的变质岩潜山凝析气田,具有储渗类型多样、特高含凝析油、应力敏感性强的特点,目前尚无类似开发实例。通过网格之间流体渗流的等效方式建立砂砾岩、半风化带、潜山内幕三类复杂储层并存的油藏模型,利用应力敏感实验获得BZ气田渗透率残余系数表达式,结合反凝析特征规律开展流体渗流-多孔介质变形动态耦合及评价。研究表明：多渗流系统精细表征及耦合是精细油藏数值模拟基础,流固耦合效应是影响开发效果影响的关键;考虑BZ气田裂缝发育,构造高部位注气易形成气顶驱,扩大波及体积;考虑反凝析特征,保持地层压力高于露点压力能最大限度降低凝析油的损失;按冬季供气需求阶段性循环注气有利于形成压力脉冲,扩大波及体积,提高凝析油采收率。研究成果对类似复杂裂缝性凝析气藏开发具有重要的指导意义。     

凝析气藏工业气流量计算方法

国土资源部颁发的《DZ/T 0217-2005 石油天然气储量计算规范》给出了我国东部地区气藏不同埋藏深度下估算的工业气流标准,但该标准没有考虑气藏储渗条件的影响,也没有明显体现凝析油成分对工业气流的影响,不适合凝析气藏的对照使用。根据投入产出平衡原理,提出了凝析气藏工业气流计算模型,以我国西部凝析气藏为例,根据目前各项参数测算了相应的工业气流,绘制了工业气流图版。提出的方法也适用于含硫化氢等其他复杂成分气藏工业气流的计算。     

川东北清溪场裂缝型气藏形成过程分析

在局部构造发育演化史、天然气的成因类型与来源、流体包裹体特征与天然气的充注史分析的基础上,分析了清溪场裂缝型气藏的天然气成藏过程。结果表明,清溪场裂缝型气藏的天然气主要为上二叠统烃源岩的干酪根裂解气;裂缝型气藏的储层的有机包裹体以天然气包裹体为主,天然气的充注时间为中-晚侏罗世;晚燕山-喜山期,大巴山的强烈挤压推覆产生构造叠加,直接导致清溪场背斜和裂缝型储集层形成,干酪根裂解气沿断裂运移至储集层形成裂缝型天然气藏;裂缝型储集层的形成与规模直接影响了天然气的充注和聚集规模。     

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.     

大张坨凝析气藏循环注气的动态监测

对于循环注气开发的凝析气藏，全过程动态监测工作十分重要，但目前国内还没有可借鉴的方法。以大张坨凝析气藏为例，建立了一套适合于凝析气藏循环注气开发的动态监测体系和监测结果的分析方法。监测对象包括开发过程中的地层压力、示踪剂运移规律和井流物组分变化。监测数据和分析结果为大张坨凝析气藏合理开发及动态调整提供了依据，从而达到提高采收率之目的。     

低渗致密气藏压裂水平井产能预测新方法

压裂水平井是有效开发低渗致密气藏和页岩气藏的主要手段,压裂水平井产能是决定非常规气藏开发成败的关键技术指标.但目前能够经济、快速地获得低渗致密气藏压裂水平井产能的方法很少.基于此,采用理想模型与数值模拟相结合的方式,得出了一种能快速评价低渗致密气藏压裂水平井产能的新方法.根据我国低渗透致密气藏的地质特点,建立了单井数值模拟模型.设计了8组16次正交试验,并对其进行了修正等时试井数值模拟.模拟结果表明,储层渗透率和储层有效厚度是影响气井产能的2个主要因素,并建立了不同裂缝条数的压裂水平井的二项式产能方程系数A和B与地层系数的经验关系.通过实例验证,该方法具有计算简单、适用性强、结果可靠的特点,能够节省大量时间和成本,适合现场快速评价应用.     

高凝析油含量凝析气藏单井衰竭式开发动态预测

饱和凝析气藏在开发过程中,地层会出现反凝析现象,各相组份及物理化学特性也会有所改变。应用PR三参数平衡状态方程拟合了凝析气藏流体PVT实验数据,建立了单井径向非均匀网格系统,应用凝析气藏多组分渗流数学模型和组分模拟软件进行预测,得到近井地带压力分布特征和凝析油饱和度分布特征,体现了近井地带反凝析液增大了流体渗流阻力。通...     

凝析气藏试井分析研究现状及展望

从渗流机理和试井理论模型两个方面对凝析气藏试井分析现状进行了回顾和评述，指出以三区流动模型为基础，采用两相拟压力的方法是目前的主要研究方向。提出了凝析气藏试井研究存在的问题，并对以后的研究方向进行了展望。     

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.     

平湖凝析气藏衰竭式开采凝析油可采储量预测

有水凝析气藏衰竭式开采凝析油采收率受到多种因素的影响,预测难度大。结合平湖油气田平湖组气藏的生产实际,提出了经验公式法、物质平衡法、动态递减法和数值模拟联解法等 4 种方法,预测计算了该气藏衰竭式开采凝析油可采储量。预测结果表明,4 种方法都具有较强的适用性。实际应用过程中可以结合实际情况选择使用,也可以进行多方法的综合评价。     

大涝坝凝析气藏循环注气注采参数优化研究

大涝坝凝析气藏在衰竭式开发过程中,受反凝析和水侵的双重影响,产能快速下降,为提高采收率,开展了循环注气开发.注采参数是影响循环注气采收率及经济效益的主要指标.针对大涝坝这类开发中后期进行循环注气的水驱凝析气藏,该文通过数值模拟方法,开展注采比、注采方式等注采参数优选,优化循环注气方案,保证了循环注气开发的效果.     

指数递减法在凝析油气藏中的应用

指数递减法是油气藏工程中的一个重要预测方法。它可以用于预测油气田递减阶段的产量、累积产量和可采储量。将指数递减用于凝听气藏的预测，取得了很好的效果，并得到了凝析气藏的总井流体产量、干气产量和凝析油产量的递减均符合指数递减的重要结论。     

雅轮凝析气藏一次完井新技术

雅轮凝析气田是一个富含凝析油的深层凝析气藏,为做好储层保护工作,同时节约时间和成本,通过优化研究,在完井时,采用油管传输负压射孔一次完井工艺。完井工艺的焦点集中在封隔器能否成功坐封、管柱伸长量多大以及液压坐封和打压射孔双重打压级别的严格设计,通过精密计算及现场实践证实了采用液压封隔器及负压射孔联作并采用先坐封后射孔这一完井新技术是可行性。该工艺的现场成功应用,对于在其它高压油气藏完井中推广该工艺具有借鉴意义。     

Analytical Production Modeling for Hydraulically Fractured Gas Reservoirs

This article presents a complete analytical method to efficiently generate gas production profiles from hydraulically fractured reservoirs. Equations for production rates are first developed incorporating fracture parameters in the diffusivity-based drawdown solutions for transient as well as pseudo steady-state flow conditions. Some important considerations for modeling the key propped-fracture parameter—dimensionless fracture conductivity—are detailed for realistic production prediction. A time-step algorithm is then discussed to apply the rate equations to generate production profiles over a period of time. Analytical equations are presented to update declining reservoir pressure and resulting rock and gas properties in every time-step as functions of cumulative gas productions. Finally, a simple new equation is developed through a series of parametric applications of the two rate equations, to determine the time to switch from the transient rate equation to the pseudo steady-state equation, particularly in low-permeability reservoirs. To establish confidence in the predictability of the model, results are verified by a numerical reservoir simulator. Thus, the model is a high potential for efficient repetitive computation in early-stage design optimization of hydraulic fracture treatments for gas reservoirs.     

低渗致密气藏压裂水平井产能预测新方法

应用位势理论、叠加原理和流体力学的相关原理,建立了考虑裂缝干扰、污染表皮、裂缝非均匀分布、裂缝与井筒有限导流,以及裂缝-井筒汇聚流、裂缝内高速非达西流动的压裂水平井稳态流动数学模型,给出了模型的数值求解方法,并运用模型预测了实际水平井产能,分析了产能的影响因素。结果表明,该模型适用性强,能用于各种复杂情况下的水平井产能预测,预测精度较高;由于裂缝间的干扰作用,各条裂缝产量存在差异,水平井筒两端裂缝产量高,中间裂缝产量低;水平井产能随水平段长度、裂缝半长、裂缝导流能力的增大而增大;裂缝污染表皮对产能影响显著,产能随表皮系数的增加而急剧下降,因此应尽量减少压裂作业对地层的伤害;在相对合理裂缝间距范围内,裂缝分布形式对产能影响不明显;井筒半径对井筒压降有影响,应根据水平井产能的高低,设计合理的井筒半径。     

牙哈23凝析气藏剩余凝析油分布规律

为达到较高的凝析油采收率,对高凝析油含量的牙哈23凝析气藏采用了回注干气的开发方式。目前气藏开发过程中的主要矛盾是部分生产井气油比升高加快,导致凝析油产量急剧下降,回注干气效果变差。从气藏地质特征分析出发,描述了储集层的非均质特征,通过对生产剖面测试、示踪剂监测和单井生产动态的研究,认为气油比上升加快的主要原因是干气突破。研究了回注干气的推进规律,根据动态分析结果对全气藏气、水相态特征及饱和度的变化规律进行了开发动态数值模拟,最终确定出剩余高凝析油含量的富集区,为气藏的开发调整、改善回注干气的开发效果、提高凝析油采收率提供依据。     

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本文在建立多层双重介质天然气藏越流问题数学模型的基础上,利用求解差分方程的最佳点超松弛叠代法,获得了它的数值解,同时还对此类油气藏的压力特征作了分析,并指出了越流研究对油气藏勘探的指导意义。     

凝析气井流入动态分析新方法

凝析气井流入动态分析是气藏工程研究，节点分析及产能计算与配产不可缺少的一部分。文中指出了现有方法利用二项式产能方程预测凝析气井流入的动态的不足，认为利用测试资料回产能方程只能用于测试阶段，而当气藏压力变化后，产能方程中的回归系数均应随气藏压力，含水饱和度，相对渗透率等的变化而变化。     

一个计算凝析气井产能的经验公式

在分析气井稳产期单井平均产能和无阻流量关系的基础上,结合单点测试计算无阻流量方法,导出了计算凝析气井产能经验公式。实测计算结果和传统试井分析方法计算结果吻合较好。方法简单实用,易于掌握。