双重孔隙介质油藏中的吸渗排油作用

利用美国SSI公司研制的COMPⅣ模拟软件对双重孔隙介质油藏一种重要的开采机理－吸渗排油－进行了模拟研究，考察了一个基质岩块为四周裂缝所包围时，在驱动压力和毛管压力的不同平衡（驱动压力和毛管压力的相对大小）关系下的水驱油采收率和水驱油效率的变化规律。     

不同驱油动力下裂缝油藏水驱方向与驱油效率的关系

本利用美国ＳＳＩ公司研制的ＣＯＭＰⅣ模拟软件对驱油分别受毛管压力控制、毛管压力和驱动压力共同控制、驱动压力控制时，裂缝油藏注水开发的水驱方向与驱油效率之间的关系进行了研究。     

砂岩孔隙结构对水驱油效率影响的研究

利用压汞毛管压力曲线求得的微观均质系数α,是表征储层孔隙结构均质程度和影响水驱油效率的主要特征参数之一.比较某些孔隙结构的特征参数与水驱油效率有更好的线性关系.并说明在一定条件下,储层孔隙结构对水驱油效率的影响主要是均质程度.本文建立了均质系数α的数学表达式,以及它与亲油、亲水岩样水驱油效率的统计关系式,应用α与水驱油效率关系等图版,预测了几个油田岩样的水驱油效率,结果与实际比较符合.     

水驱微观渗流特征及剩余油启动机理

通过微观驱油实验、岩心驱油实验及渗流理论分析,明确了水驱微观渗流规律,量化了水驱后微观剩余油分布特征,提出了改善水驱效果及提高采收率方法机理。水驱后剩余油启动需要克服启动压力,按照驱油机理划分,水驱后剩余油可划分为受黏附力控制的剩余油和受毛管力、黏滞力控制的剩余油2种类型,其中受毛管力和黏滞力控制的剩余油占90%以上。通过增加驱替压力梯度、降低界面张力启动和增加驱替体系黏度可以提高油层采收率。     

复合驱驱油过程中存在两种不同驱动状况

油藏数值模拟研究发现,驱油过程中,随着毛管数增大,驱油效果改善,但当毛管数超过一定范围,出现驱油效果相对变差变化.通过对不同毛管数条件下驱油过程的细致分析研究发现,在毛管数超过一极限后,出现水相流速相对加大变化,即发生驱动状况变化.这一研究结果已经得到了驱油实验的验证,而且在现场试验中也找到了证据.详细介绍了证实复合驱油过程中存在两种不同驱动状况的驱油实验研究过程和结果以及现场驱油试验存在两种不同驱动状况的证据.     

数值模拟发现复合驱油过程中存在两种不同驱动状况

油藏数值模拟研究驱油方案过程中发现,驱油过程中,毛管数增大,驱油效果改善,但当毛管数超过一定范围,出现驱油效果相对变差变化.对不同毛管数条件下驱油过程研究得出,在毛管数超过一极限毛管数后,出现水相流速相对加大变化,即发生了驱动状况变化.通过深入剖析两种驱动状况,找到了模拟计算出现驱动转化的原因是来自于软件有关相渗透率曲线的描述.结论不仅得到了实验验证,而且在现场试验中找到了证据,在此基础上又完成了新的毛管数实验曲线.研究成果,可为复合驱技术的实际应用提供指导.     

单变量相分异指数在驱油效率分微相研究中的应用

针对分微相研究驱动压差与最终驱油效率关系时逐步判别分析方法消除各类干扰因素所存在的不足,引入了单变量相分异指数UFDI来定量表征某类变量在不同沉积微相之间的分异性,区分已消除和未消除的干扰因素.在留楚油田沙一段储集层的水驱油实验和其他相关实验测定数据的基础上,进行单变量相分异指数的计算,结果表明孔隙度和渗透率对最终驱油效率的影响并不能通过分沉积微相来消除.按照毛管压力的平均方法对驱动压差进行标准化后,最终建立了理想的驱动压差与最终驱油效率关系曲线,得到了各沉积微相驱动压差对最终驱油效率的不同影响规律.图3表2参10     

油层岩石的孔隙结构与驱油效率的关系

根据岩石的毛管压力曲线资料．在矩法确定的岩石孔隙结构特征值基础上,提出了孔隙结构特征值函数的方法．室内驱油实验结果证明,孔隙结构特征值函数与水驱油效率有很好的正相关性,利用孔隙结构特征值函数可以预测油藏的水驱油效率．     

油层岩石的孔隙结构与驱油效率的关系

根据岩石的毛管压力曲线资料,在矩法确定的岩石孔隙结构特征值基础上,提出了孔隙结构特征值函数的方法。室内驱油实验结果证明,孔隙结构特征值函数与水驱油效率有很好的正相关性,利用孔隙结构特征值函数可以预测油藏的水驱油效率。     

扶余油田储油层的均质系数与水驱效率的关系

通过压汞样品的毛管压力曲线计算出均质系数值。根据样品实测的含油饱和度,求出目前水驱油的效率,进行数理统计处理后,求出均质系数与矿场目前水驱效率的关系式,这对了解油田的水驱效果,指导油田注水开发和提高驱油效率都有一定的意义。     

粘弹性流体平行于界面的力可以提高驱油效率

水驱后残余油的微观形态可划分为油滴状、油膜状和簇状残余油3种类型.前人研究工作表明,若要用牛顿流体驱动水驱后的残余油,其驱动力必须要再增加1000～10000倍才能克服束缚残余油的毛管力,而实际油藏中的粘滞力不可能增加如此之大.虽然聚丙烯酰胺水溶液对油水界面张力影响不大,但实验室内和矿场试验数据表明,用聚合物水溶液驱替后,孔隙介质中所有类型的残余油均减少,减少的量取决于驱替液的弹性.实验条件相似的流体,其弹性越大,驱替后残余油饱和度越低.微观可视岩心模型实验研究结果证实,粘弹性驱替液可降低不同润湿性岩心的残余油饱和度.粘弹性驱替液驱替残余油的力与牛顿流体的力不尽相同,它不仅有垂直于油水界面克服束缚残余油的毛管力,而且还有较强的平行于油水界面驱动残余油的拖动力.     

Interfacial Coupling in Vertical, Two-Phase Flow Through Porous Media

Vertical, two-phase flow through natural porous media is affected by interfacial coupling. Such coupling may be of two types: viscous and capillary. In this study, macroscopic defining equations for the viscous and capillary coupling parameters have been constructed. Moreover, these defining equations, together with modified forms of Kalaydjian's transport equations, have been used to construct equations that can be used to analyze the effect of interfacial coupling on vertical, two-phase flow in natural porous media. These equations reveal that viscous coupling is dependent explicitly on mobility ratio, and that the effect of viscous coupling on vertical flow is bounded. Moreover, these equations show that capillary coupling depends explicitly on porosity. Furthermore, on the basis of the analysis carried out, it is argued that the effect of viscous coupling on vertical flow is small, and that the effect of capillary coupling on horizontal flow is an order of magnitude larger than that of viscous coupling. The data from two sets of gravity-driven, steady-state, cocurrent and countercurrent flow experiments were used to test the interfacial coupling theory. It was found that the experimentally determined and predicted values of the capillary coupling parameters were consistent for both the wetting and the nonwetting phase, provided proper account was taken of the contribution of the net buoyant force to the driving force for each phase. Because of a lack of sufficient experimental evidence, further experimental testing of the theory must be undertaken before it can be accepted with confidence. Even so, the new equations should be, because they show explicitly the role of mobility ratio and porosity, useful tools for improving our understanding of the effect of interfacial coupling on vertical, two-phase flow through natural porous media.     

Interfacial Coupling in Vertical,Two-Phase Flow Through Porous Media

Abstract:

Vertical, two-phase flow through natural porous media is affected by interfacial coupling. Such coupling may be of two types: viscous and capillary. In this study, macroscopic defining equations for the viscous and capillary coupling parameters have been constructed. Moreover, these defining equations, together with modified forms of Kalaydjian's transport equations, have been used to construct equations that can be used to analyze the effect of interfacial coupling on vertical, two-phase flow in natural porous media. These equations reveal that viscous coupling is dependent explicitly on mobility ratio, and that the effect of viscous coupling on vertical flow is bounded. Moreover, these equations show that capillary coupling depends explicitly on porosity. Furthermore, on the basis of the analysis carried out, it is argued that the effect of viscous coupling on vertical flow is small, and that the effect of capillary coupling on horizontal flow is an order of magnitude larger than that of viscous coupling. The data from two sets of gravity-driven, steady-state, cocurrent and countercurrent flow experiments were used to test the interfacial coupling theory. It was found that the experimentally determined and predicted values of the capillary coupling parameters were consistent for both the wetting and the nonwetting phase, provided proper account was taken of the contribution of the net buoyant force to the driving force for each phase. Because of a lack of sufficient experimental evidence, further experimental testing of the theory must be undertaken before it can be accepted with confidence. Even so, the new equations should be, because they show explicitly the role of mobility ratio and porosity, useful tools for improving our understanding of the effect of interfacial coupling on vertical, two-phase flow through natural porous media.     

多孔介质中气水渗流的微观机理研究

利用微观玻璃模型进行了气水两相渗流微观机理研究.孔隙水平的直观观察表明:气水两相排驱和渗吸的微观渗流机理截然不同,低流速时虽然二者均受毛管力的影响,但排驱时气水前缘始终沿连续的大喉道路径运移,存在明显的跳跃式运移现象;速度较高时,有明显的粘性指进现象,气体前缘呈树枝状,随流速的增加,分叉更多.而低速渗吸时水沿壁进入孔隙,首先充满小喉道,发生严重的毛管指进,并沿壁能到达孔隙模型的各个角落,前缘推进随流速的增加而变得均匀.实验结束后的气水微观分布分析,对提高油气采收率的研究具有指导意义.      

Formation mechanism of micro-flows in aqueous poly（ethylene oxide） droplets on a substrate at different temperatures

The drying of aqueous poly(ethylene oxide)(PEO) droplet on a substrate at different temperatures was studied.It was found that the contact line receded when the substrate was at a temperature above 60 oC.Different nucleation behavior and surface profiles of PEO films were found in different droplets drying processes.The rheological properties of aqueous PEO solutions were studied to understand the mechanism of contact line recession and micro-flow in drying aqueous PEO droplets.It was found that at low temperature,the contact line was static because of great viscous stress;while at high temperature,it receded because of great Marangoni force and the decrease of viscous stress.It was indicated that Marangoni convection was inhibited by the outward capillary flow and viscous stress at low temperature,whereas it became dominant at high temperature.Two types of mechanism for surface profiles and nucleation of PEO film from drying droplets are proposed,providing a theoretical guide for polymer solution application in oil and gas foam flooding technology.     

Experimental Testing of Interfacial Coupling in Two-Phase Flow in Porous Media

Two-phase flow through natural porous media is affected by the interfacial coupling that takes place across the interfaces located in a porous medium. Such coupling may be of two types: viscous and capillary. In this study, defining equations for the capillary and viscous coupling parameters have been constructed. Moreover, these equations, together with a modified form of Kalaydjian's transport equations, have been used to analyze interfacial coupling in two-phase flow through porous media. On the basis of the analysis carried out, it is argued that interfacial coupling has no effect on steady-state, cocurrent flow, and only a small effect on unsteady-state, cocurrent flow. Moreover, it is suggested that interfacial coupling has a significant effect on steady-state, countercurrent flow. Two methods were used to test the theory. In the first method, data from steady-state, cocurrent, and countercurrent experiments were used to show that experimentally determined values of the capillary coupling parameters were in good agreement with those predicted theoretically. Because of experimental problems, it was not possible to determine experimentally, when using the first method, the magnitude of the viscous coupling parameters. In the second method, data from steady-state and unsteady-state, cocurrent flow experiments, using fluids having different viscosity ratios, and porous media having different grain-size distributions, were used to test the theory. Because of a lack of sufficient precision in the measured data, it was not possible to make definitive statements with respect to the adequacy of the theory, or the possible impact of viscosity ratio and grain-size distribution on capillary coupling. Moreover, for the same reason, it was not possible to obtain reliable estimates of the magnitude of the capillary coupling parameters. Because the second method is based on the assumption that viscous coupling is negligible, it was not possible to use this method to determine experimentally the magnitude of the viscous coupling parameters.     

储层油水两相动态毛管力测试方法

针对目前毛管力测试方法无法准确反映出渗流过程中毛管力的动态变化问题,在借鉴气水两相动态毛管力的基础上,提出了油水两相动态毛管力的概念,并制作了动态毛管力测试装置。利用半渗透薄膜分别制作了单独测量油相和水相的压力传感器,在人工胶结岩心两个表面对称制作了8个压力测试点,采用环氧树脂将油相压力传感器与水相压力传感器紧密固定在人工胶结岩心上,采用类似稳态法测相渗曲线的实验流程,注入比例恒定的油水混合液体,测试不同饱和度条件下的毛管力。利用动态毛管力测试仪,对人工胶结岩心的动态毛管力进行了测量,得到了3条不同驱替速度条件下的动态毛管力曲线,分析发现,不同驱替速度条件下的毛管力数值存在差异,并且会对水驱油过程的数值计算带来较大影响。     

正韵律厚油层注气提高上部层段采收率的试验研究

按照相似原理,应用自己研制的油层物理模型,对正韵律厚油层注气提高上部层段采收率进行了实验研究。在非混相条件下,研究了油、气、水三相在不同地质特征的正韵律油层模型中的渗流机理;并且观察到在重力、粘滞力和毛管力作用下,油、气、水运动的特征及纵向分布特点。研究表明:油层地质特征是决定注气效果的关键;产出气液比是反映注气效果的重要指标。为开展渗流物理实验研究,研制了5～9米长的物理模型和油、气、水三相分离器,及进、出口计量等一套装置。对比了物理模拟实验和数值模拟研究结果,得出结论是一致的。为大庆油田正韵律厚油层现场注气试验提供了依据。     

Pressures acting in counter-current spontaneous imbibition

Four water/oil and four oil/air linear counter-current spontaneous imbibition experiments were performed on Berea sandstone cores with permeabilities ranging from 0.065 to 1.094 μm². The cores were initially 100% saturated with non-wetting phase and all faces except one end were sealed. The experiments showed a clear frontal displacement mechanism. Capillary pressure was the driving force of the imbibition process. As well as viscous drag in both phases between the imbibition front and the open face, there is a significant opposing capillary back pressure associated with production of non-wetting phase at the open face. The location of the imbibition front, the overall changes in core saturation, and the pressure in the nonwetting phase in the dead end space ahead of the imbibition front, were monitored during the course of imbibition. The dead end pressure was essentially constant after a short start-up period. The distance advanced by the imbibition front was proportional to the square root of time. Based on the assumption that the properties of Berea sandstone of different permeabilities can be scaled, the experimental data were matched by numerical simulation to predict the saturation and pressure profiles, the saturation and capillary pressure at the imbibition front, and the capillary back pressure at the open face. The ratio of the capillary back pressure to the estimated capillary pressure at the imbibition front ranged from approximately 1/3 to 2/5, for oil displacing air, to approximately 1/9 to 1/4, for water displacing oil.