Enhanced Shale Oil Recovery by the Huff and Puff Method Using CO₂ and Cosolvent Mixed Fluids

Abstract

Shale oil, as one of the unconventional resources, has become increasingly important to supplement conventional oil and gas. Although CO 2 has great potential to enhance shale oil recovery by the huff and puff method, the experimental results show that the enhanced values of shale oil recovery are unstable and have great fluctuations for different cores. In order to increase the stability of CO 2 huff and puff and further enhance oil recovery, cosolvents such as ethanol, isopropanol, ethyl acetate, and acetone were chosen to construct CO 2 /cosolvent mixed fluids and the experiments of huff and puff by the mixed fluids were carried out. The results show that CO 2 /cosolvents can enhance the shale oil recoveries of the matrix and fracture. CO 2 /ethanol has the highest oil recovery among the mixed fluids. In particular, for cycles 2 and 3 in the huff and puff process, CO 2 /ethanol has a much larger oil recovery than CO 2 . Moreover, the effects of ethanol concentration in the mixed fluids on the enhanced shale oil recovery were investigated. The enhanced oil recoveries by CO 2 /ethanol mixed fluids increase with the increase of ethanol concentration. Furthermore, the mechanisms to enhance shale oil recovery by CO 2 /cosolvent fluids were discussed by measurements of the pressure decay process and interfacial tension. The presence of ethanol can not only accelerate the transfer of CO 2 to the oil phase in the porous media during the huff process, to make more CO 2 transfer into the oil phase, but also decrease the interfacial tension between oil and CO 2 as well as the minimum miscibility pressure, to make oil and CO 2 mixed fluids have a longer time to flow out in one phase than CO 2 in the puff process. Therefore, the CO 2 /cosolvent mixed fluids, especially CO 2 /ethanol, can be used to further enhance shale oil recovery during the huff and puff process.

Synthesis and structural characterization of CO2-soluble oxidizers [Bu4N]BrO3 and [Bu4N]ClO3 and their dissolution in cosolvent-modified CO2 for reservoir applications

“…Recent studies on the solubility of light hydrocarbons in CO 2 demonstrated notable improvements when cosolvent was added to the uid. 17,18 The current application requires that only small amounts of oxidizing salts be dissolved in CO 2 . For subterranean applications where oxidizers are utilized in aqueous uids, concentrations are typically in the range of a few pounds per thousand gallons of uid (<0.1 wt%).…”

Effects of Shale Pore Size and Connectivity on scCO2 Enhanced Oil Recovery: A Molecular Dynamics Simulation Investigation

“…Under the current situation of increasingly depleted resources, traditional oil resources are gradually unable to satisfy the increasing energy requirement. − It is reported that shale oil accounts for a large proportion of the total energy supply as the conventional oil production gradually declines in recent years. Therefore, the development of shale oil plays a crucial role in alleviating the current problem of energy shortage. , Shale reservoirs are typical multi-scale porous media, in which the nanopores are extremely developed and have ultra-low permeability, making it difficult to exploit. − Multifarious approaches have been employed to improve the recovery of shale oil, such as chemical flooding, gas injection, thermal recovery, and smart water flooding. , Despite extensive attempts on thermal recovery, chemical flooding, and water flooding, applications are limited due to abominable reservoir conditions, high costs, and damage to the formation. , Gas (such as CO 2 , N 2 , and natural gas) injection-enhanced oil recovery is gradually appreciated due to their environmental protection and high efficiency. − Compared with other gases, CO 2 is supercritical under high-temperature and pressure conditions in shale reservoirs, possessing tremendous advantages and unique properties, such as a high diffusion rate and favorable dissolution capacity. , Because of these properties, CO 2 injection is regarded as an extremely promising EOR method.…”

Rough Surface Effect on CO2 Displacement at the Nanoscale

“…5,6 In light of these challenges, CO 2 injection shows great potential as a complementary energy source for shale formations. 7,8 CO 2 has a relatively high mobility in shale and can dissolve in shale oil to lower its viscosity. 9−11 Furthermore, CO 2 is preferentially adsorbed in kerogen, displacing light hydrocarbons.…”