A Sequential Polymer Injection Treatment Using RPM: Effects of Multilayer Adsorption of Cationic and Anionic Polymers

摘要

Relative permeability modifiers (RPMs) have proven to be an effective technology to control water production without significantly damaging hydrocarbon-production potential. Systems most commonly used for this purpose are single solutions of water soluble, high molecular weight polymers that adsorb onto the pore surface and change the flow properties of the porous media. However, these adsorbed polymers are only developed thin single film layer on the pore surfaces, resulting in a moderate success to maximize the water controlling efficiency. Moreover, high molecular weight injecting polymers can cause inaccessible pore volumes (IPVs), resulting in the failure of controlling water production for a long period of time. Because blocking polymer chains in front of IPVs can easily be penetrated due to strong water resistance after the treatment. To overcome this unsuccessful scenario, this paper presents the laboratory development of a novel polymer injection system, which is a sequential injection of polymers considering ionic characteristic as well as controlling molecular weight, injection volume and concentration. When cationic and anionic polymers are injected sequentially into a sandstone formation, a first injected cationic polymer induces preferential adsorption onto the negatively charged sandstone pore surfaces. Thereafter, anionic and cationic polymers are injected stepwise. These injecting polymers will be adsorbed and stacked making multiple adsorbed layers by electrostatic interactions, which results in a higher level of hindrance to water flow while still maintaining the minimal effect on hydrocarbon flow. Furthermore, increasing molecular weight and concentration of polymers can be injected sequentially to reduce IPVs. Injection volume can be designed to decrease to simulate maximum water controlling efficiency near wellbore regions. Experimental results from Berea cores showed that there are improvements in Frrw values (up to 9.29) and Frrw/Frro ratios (up to 3.34) in a sequential injection process compared to conventional single injection processes. Frrw/Frro ratios showed an improving tendency with pore volume injected until the ends of experiments. The obtained results clearly indicate the effectiveness of sequential injection method in verifying improved RPM performance.