Efficacy of Surfactants in Rich Gas Shale Wells

Abstract

Abstract Foam lift has proven to be an effective method to mitigate liquid loading in unconventional resource (UCR) wells. Water-soluble surfactants are commonly used when liquid loading is mainly caused by formation water. There is a larger uncertainty involving the efficacy of water-soluble surfactant at water cuts below 80%. Therefore, oil-soluble surfactants are recommended. However, high oil-soluble surfactant price causes a significant increment in Opex, which can make the well production uneconomical. Flow loop tests have been carried out in a closed-loop 2″ ID facility to emulate continuous backside foam injection. The oil condensate is emulated using a low density commercial isoparaffin oil, while tap water and compressed air are used instead of formation water and natural gas. The experiments are conducted at water cut values that range between 70% and 100% for surfactant concentration of 250 ppm. The foamer surfactant is a commercial water-soluble surfactant that is commonly used in oil field applications. The liquid loading onset is primary parameter obtained from each test through video and data analysis. Other parameters such as flow pattern and pressure gradient are also reported. The experimental results show that liquid loading initiates at gas flow rates around 252 MSCFD for air-water flow in a 2-in. ID tubing. Adding the condensate fraction with a fixed total liquid rate and no surfactant slightly increases the critical gas rate. After surfactant injection, the reduction in critical gas flow rate is approximately 40% for most water cuts except the case of 70% water cut, where the oil presence seems to inhibit the surfactant effectiveness. Visual observations at this case show a significant reduction in generated foam, and relatively similar flow pattern transitions as the case of no surfactant. These results demonstrate that water-soluble surfactants are very effective in mitigating liquid loading at high water cuts, but their effectiveness reduces as water cut decreases. This causes an increase in the critical gas flow rate despite foam injection. Currently, most operators aim to produce from condensate-rich shale in order to increase profit. The results of this study offer a first look in the following two issues. First, the effect of oil in liquid loading is investigated and the effectiveness of surfactant at different water cuts is evaluated. Second, the results can be used to design cost effective treatments based on water-soluble surfactants. Most literature about the effect of water cut on surfactant injection effectiveness is based on small scale lab. This experimental study is one of the few flow loop tests to investigate the effect of oil on the onset of liquid loading with surfactant.