Effects of a Viscoelastic Surfactant on Supercritical Carbon Dioxide Thickening for Gas Shale Fracturing

Abstract

Among waterless fracturing fluids, supercritical carbon dioxide (Sc-CO 2 ) has been increasingly emphasized in recent years for hydrocarbon recovery from shale. Sc-CO 2 is the most feasible choice to be an alternative to conventional hydraulic fracturing with the ability to alleviate global warming. However, Sc-CO 2 fracturing is encumbered with problems such as poor proppant-carrying capacity, easy sand plugging, large displacement, and high frictional resistance. The main aim of this study is to investigate the thickening of Sc-CO 2 by adding viscoelastic surfactants (VESs) for increasing the proppant-carrying capacity and to understand the preferential adsorption of this thickened Sc-CO 2 over methane on a heterogeneous molecular shale model. From the literature, it was found that a fluorinated polymer provides good CO 2 solubility and also thickens CO 2 . As a result, fluorinated VES, N-ethyl perfluorooctyl sulfonamide (N-ETFOSA), and nonfluorinated VES, N,N,N′-trimethyl-1,3-propanediamine (N,N,N′-TM-1,3-PDA), were used in this study for comparison. The molecular simulation of thickening Sc-CO 2 employing N-ETFOSA and N,N,N′-TM-1,3-PDA was carried out at a temperature and pressure ranging from 298 to 305 K and 100 to 7400 kPa, respectively. Although N,N,N′-TM-1,3-PDA shows better solubility in Sc-CO 2 than N-ETFOSA, both of them cause an increase in the viscosity of Sc-CO 2 by 36 and 156 times, respectively, than its actual viscosity. Adsorption simulations of CO 2 -thickened Sc-CO 2 and methane (CH 4 ) were performed on a heterogeneous molecular shale model. With increasing pressure at a constant temperature, N-ETFOSA-thickened Sc-CO 2 showed better adsorption capacity on the molecular shale model than others. Accordingly, at higher pressure, N-ETFOSA-thickened Sc-CO 2 shows better selectivity over methane. The results of viscosity and adsorption simulations have been validated by literature experiments. Nonetheless, these outstanding simulation findings need more experimental backup to pave their implementation on real field scenarios. Thus, this study helps establish a theoretical ground for the optimization of shale gas extraction from shale plays and makes it viable storage for CO 2 sequestration.

Application and Research Progress of CO2 Stimulation Technology in Unconventional Oil and Gas Reservoirs: A Review and Prospect

“…Meanwhile, cumulative oil production reached 8500 t. It is expected that the final cumulative oil production can reach 80 000 t. Meanwhile, the recovery rate can increase by 12.3%. Eventually, the recovery rate can reach 20% …”

“…Eventually, the recovery rate can reach 20%. 34 CO 2 flooding contains many branch technologies. CO 2 foam flooding technology is one of them.…”

“…In addition, CO 2 dry foam fracturing technology can use nitrogen foam to improve viscosity, stability, and sand-carrying capacity . At present, CO 2 thickeners in the world are generally divided into four categories: surfactant, hydrocarbon polymer, fluorine-containing polymer, and siloxane polymer. − CO 2 thickeners at home and abroad are shown in Table .…”