Effects of Nanopores on Carbon Dioxide Enhanced Oil Recovery in Tight Oil Reservoirs
Abstract
Horizontal well drilling with multi-stage hydraulic fracturing is mainly applied in tight oil exploitation. In some tight carbonate reservoirs like Pekisko, acidizing is applied. The primary recovery factor, however, remains below 10% even with advanced technologies. Water flooding has also been proposed for tight oil development, but water can form a membrane up to 43 nm, which tremendously hinders water injectivity. A CO2 miscible process seems a promising technique to enhance tight oil recovery.
The mechanism of CO2-oil miscibility is the separation of oil molecules by the CO2 introduced; van der Waals forces that hold the oil molecules together need to be overcome. The process is similar to the vaporization of a liquid. The energy added into the liquid is used to overcome the van der Waals forces that hold the molecules of the liquid together, separate the liquid molecules and split them into the gas phase.
In a nanoscale pore medium, variations in molecular orientation and molecules arrangement result in an alteration in the van der Waals forces, thereby creating unique thermal dynamic properties. These contribute to changes in CO2-oil miscibility compared to that in conventional reservoirs. At present, no systematical study addresses CO2-oil miscibility in nanopores.
To unlock the mysteries of CO2 in enhanced oil recovery (EOR) in nanopores, the interactions between nanopores and molecules are studied using armchair, a zig-zag carbon nanotube, cubic shape smooth and rough nano-channels, and nano-channels with a functional group OH. The molecules trajectory and potential energy can be recorded by molecular dynamics simulations. The CO2-oil miscibility in nanopores is further presented including phase equilibrium, vaporizing and condensing drive, immiscible and miscible processes, and solubility parameters. The nanopore effect can be applied in screening candidate reservoirs for CO2 flooding and in selecting CO2 parameters by reservoir simulations.
The thesis can be very revealing to researchers in the area of CO2-oil miscibility in nanopores.
Description
Keywords
Engineering--Petroleum
Citation
Zhang, K. (2017). Effects of Nanopores on Carbon Dioxide Enhanced Oil Recovery in Tight Oil Reservoirs (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from https://prism.ucalgary.ca. doi:10.11575/PRISM/25829