水驱油过程中的动电效应

Electrokinetic effect in water-oil displacement

流动电位是动电效应的一种,其产生与岩石和流体的性质有关.通过测量渗流过程中的流动电位效应不仅可以反映地层性质,还有可能反映压力和饱和度的变化.当前能够帮助识别油层出水位置和方向的方法众多,但探测距离有限;地球物理学界普遍认为,使用流动电位方法有助于解决该问题,因为油、气、水三种流体化学性质上存在明显极性差异,且油井生产中压力会伴随随着生产制度而人为改变,同时电位效应传播的距离较通常方法更远,特别是智能完井技术的进步为井下传感器的安装创造了条件.本文通过实验获得了填砂条件下一维水油单相流动及两相流动时的流动电位和压力数据,并根据实验参数建立渗流和电流的耦合数学模型对物理模拟实验进行了解释.结果显示单相流动中,油、水的两种流体的动电效应存在明显差异,水相流动时的电效应比油相大一个数量级;而水驱油过程中,随着注入水向生产井的推进,电位值逐渐增大,数值模拟结果显示电位的峰值出现在油水前缘位置与实验结果趋势一致,该结果对电测井曲线挖潜和新颖油藏动态监测工具的开发具有指导意义.

Streaming potential （SPs） is one kind of electrokinetic phenomena that are generated through coupling mechanism. It arises from fluid flow through porous media under pressure gradient, which could be used to invert properties of reservoir, pressure and saturation variation. Interest in application of SPs method to geosciences has been growing for years, such as hydrology, geothermal and mineral exploration. Although many techniques can help us with identifying depth and orientation of water-outlet layer, however detecting distance is limited; The present research home and abroad shows that streaming potential method in theory is helpful to deal with this challenge, because electrokinetic properties are very different among oil/water and gas water system, and reservoir pressure vary with manual controlled production rate, electrical current is able to conduct in the lithosphere more widely; especially with advancement of intelligent well technique multi-sensor could be fixed downhole which is more convenient for electrical signal measurement. In the paper, we are interested in whether streaming signal is measurable in unconsolidated sand physical model and have the tendency with the coming of water. We performed 1D water-oil displacement experiment in a acrylic tube with insulate boundary condition, recorded pressure and voltage data simultaneously with different pump flow rate, and established numerical model based on coupling flow theory to compare with the experiment. The result shows there is significant discrepancy between oil flow and water flow in signal phase flow period, coupling parameter is nearly one order larger in water flow than in oil. In multiphase flow, the numerical model shows that voltage peakappears at oil-water front, descented to each side, and going toward to the production well, this is in line with physical experiment data. So, we can conclude that streaming potential is useful to identify the potential zone from electrical logging data and is probably a new kind of reservoir dynamic monitoring method.