Abstract
Surfactant-based EOR has thus far been demonstrated to be a potentially effective solution to improve the hydrocarbon recovery from Unconventional Oil Reservoirs (UORs). The most discussed functions of a surfactant are either Interfacial Tension (IFT) reduction or Wettability (WTA) Alteration. However, studies of the accountable effects for the enhanced production are inadequate because of the peculiar properties of shale matrix, such as the extremely low permeability and initial wetness. In addition, the current studies mainly focused on the spontaneous imbibition (SI) because of the long experimental period and limited pressure applicability with the existing experimental apparatus.
This work is to study the process of shale oil EOR by adding surfactant additives with high confining pressures applied to an in-house designed set-up. The applied pressure was as high as 3000 psi and the surfactant was selected with a spectrum of IFT values. Two operational schemes were conducted: Forced Imbibition (FI) and Cyclic Injection (CI). For the forced imbibition study, constant pressure was applied to the experimental set-up throughout the whole experimental period. The final recovery was recorded at the end of each test. The cyclic injection is also referred to as ‘huff-n-puff’ technique. The pressure is applied and released with a periodic schedule and the recoveries were recorded after each cycle by volume.
The results were compared with that of regular SI experiments. It is noticed that oil productions through the CI technique is mostly effective and efficient. In addition, WTB-alteration is the dominating mechanism in both pressurized and atmospheric pressure cases, while surprisingly, IFT-reduction could be detrimental for the recovery enhancement due to the low capillary pressure. The results gave indicative suggestions on the selection of surfactant and engineering application design for a surfactant based EOR project in shale oil reservoirs.
