Flow behavior of N2 huff and puff process for enhanced oil recovery in tight oil reservoirs
In the present work, the potential of N2 huff and puff process to enhance the recovery of tight oil reservoir was evaluated. N2 huff and puff experiments were performed in micromodels and cores to investigate the flow behaviors of different cycles. The results showed that, in the first cycle, N2 was dispersed in the oil, forming the foamy oil flow. In the second cycle, the dispersed gas bubbles gradually coalesced into the continuous gas phase. In the third cycle, N2 was produced in the form of continuous gas phase. The results from the coreflood tests showed that, the primary recovery was only 5.32%, while the recoveries for the three N2 huff and puff cycles were 15.1%, 8.53% and 3.22%, respectively.The recovery and the pressure gradient in the first cycle were high. With the increase of huff and puff cycles, and the oil recovery and the pressure gradient rapidly decreased. The oil recovery of N2 huff and puff has been found to increase as the N2 injection pressure and the soaking time increased. These results showed that, the properly designed and controlled N2 huff and puff process can lead to enhanced recovery of tight oil reservoirs.
CO2 injection for enhanced oil recovery in Bakken tight oil reservoirs
The combination of horizontal drilling and multi-stage hydraulic fracturing have boosted the oil production from Bakken tight oil reservoirs. However, the primary oil recovery factor is very low due to the extremely tight formation, resulting in substantial volumes of oil still remaining in place. Hence, it is important to investigate the potential of applying enhanced oil recovery methods to increase oil recovery in the Bakken formation. Although carbon dioxide (CO2) is widely used in conventional reservoirs to improve oil recovery, it is a new subject and not well-understood in unconventional oil reservoirs such as the Bakken formation. In this paper, we use numerical reservoir simulation to model CO2 injection as a huff-n-puff process with typical reservoir and fracture properties from the Bakken formation. Effects of CO2 molecular diffusion, number of cycle, fracture half-length, permeability and reservoir heterogeneity on the well performance of CO2 huff-n-puff are examined in detail. The results show that the CO2 diffusion plays a significant role in improving oil recovery from tight oil reservoirs, which cannot be neglected in the reservoir simulation model. Additionally, the tight oil formation with lower permeability, longer fracture half-length, and more heterogeneity is more favorable for the CO2 huff-n-puff process. This work can provide a better understanding of the physical mechanisms and key parameters affecting the effectiveness of CO2 injection for enhanced oil recovery in the Bakken formation.
The MR-TOF-MS isobar separator for the TITAN facility at TRIUMF
At TRIUMF’s Ion Trap for Atomic and Nuclear Science (TITAN) a multiple-reflection time-of-flight mass spectrometer (MR-TOF-MS) will extend TITAN’s capabilities and facilitate mass measurements and in-trap decay spectroscopy of exotic nuclei that so far have not been possible due to strong isobaric contamination. This MR-TOF-MS will also enable mass measurements of very short-lived nuclides (half-life > 1 ms) that are produced in very low quantities (a few detected ions overall). In order to allow the installation of an MR-TOF-MS in the restricted space on the platform, on which the TITAN facility is located, novel mass spectrometric methods have been developed. Transport, cooling and distribution of the ions inside the device is done using a buffer gas-filled RFQ-based ion beam switchyard. Mass selection is achieved using a dynamic retrapping technique after time-of-flight analysis in an electrostatic isochronous reflector system. Only due to the combination of these novel methods the realization of an MR-TOF-MS based isobar separator at TITAN has become possible. The device has been built, commissioned off-line and is currently under installation at TITAN.