Farajzadeh R, Guo H, van Winden J, Bruining J
Shell Global Solutions International, 2288 GS Rijswijk, The Netherlands.
Delft University of Technology, 2628 CD Delft, The Netherlands.
ACS Earth Space Chem. 2017 Apr 20;1(2):101-112. doi: 10.1021/acsearthspacechem.6b00015. Epub 2017 Mar 16.
Cation exchange is an interfacial process during which cations on a clay surface are replaced by other cations. This study investigates the effect of oil type and composition on cation exchange on rock surfaces, relevant for a variety of oil-recovery processes. We perform experiments in which brine with a different composition than that of the in situ brine is injected into cores with and without remaining oil saturation. The cation-exchange capacity (CEC) of the rocks was calculated using PHREEQC software (coupled to a multipurpose transport simulator) with the ionic composition of the effluent histories as input parameters. We observe that in the presence of crude oil, ion exchange is a kinetically controlled process and its rate depends on residence time of the oil in the pore, the temperature, and kinetic rate of adsorption of the polar groups on the rock surface. The cation-exchange process occurs in two stages during two phase flow in porous media. Initially, the charged sites of the internal surface of the clays establish a new equilibrium by exchanging cations with the aqueous phase. At later stages, the components of the aqueous and oleic phases compete for the charged sites on the external surface or edges of the clays. When there is sufficient time for crude oil to interact with the rock (i.e., when the core is aged with crude oil), a fraction of the charged sites are neutralized by the charged components stemming from crude oil. Moreover, the positively charged calcite and dolomite surfaces (at the prevailing pH environment of our experiments) are covered with the negatively charged components of the crude oil and therefore less mineral dissolution takes place when oil is present in porous media.
阳离子交换是一个界面过程，在此过程中，粘土表面的阳离子被其他阳离子所取代。本研究调查了油的类型和成分对岩石表面阳离子交换的影响，这与多种石油采收过程相关。我们进行了实验，将成分与原地盐水不同的盐水注入有和没有剩余油饱和度的岩心中。使用PHREEQC软件（与多功能输运模拟器耦合），以流出液历史的离子组成作为输入参数，计算岩石的阳离子交换容量（CEC）。我们观察到，在原油存在的情况下，离子交换是一个动力学控制的过程，其速率取决于油在孔隙中的停留时间、温度以及极性基团在岩石表面的吸附动力学速率。在多孔介质中的两相流过程中，阳离子交换过程分两个阶段发生。最初，粘土内表面的带电位点通过与水相交换阳离子建立新的平衡。在后期阶段，水相和油相的成分竞争粘土外表面或边缘的带电位点。当有足够的时间让原油与岩石相互作用时（即当岩心用原油老化时），一部分带电位点会被原油中的带电成分中和。此外，在我们实验的主导pH环境下，带正电的方解石和白云石表面被原油的带负电成分覆盖，因此当多孔介质中存在油时，矿物溶解较少发生。
