NMR and CT characterizing the influence of O2 in air injection performance in shale oil cores

Abstract

BackgroundThe primary objective of this paper is to evaluate the performance of extracting shale oil resources by air injection experiments. In this paper, the shale cores were acquired from Xinjiang Permian Lucaogou formation, with an average porosity of 14% and an average permeability of 0.3mD. 2) Method: The remaining oil distribution and mobilization of oil saturation was characterized by online NMR spectra and X-ray CT scanner. Nitrogen, 8% oxygen of air and 16% oxygen of air injection were evaluated for their enhanced shale oil recovery performance. 3) Significant findings: With the increase of oxygen concentration in the air, a higher oil recovery factor was yielded. Under different O2 concentration, oil recovery factor by nitrogen drive is 45.31%, and the highest (16% oxygen) is 69.81%. Most of hydrocarbons were produced from the 1～5 μ m pore size. Approximately 50% of oil was recovered by the first 0.6 PV of air injection. Oil recovery efficiency is remarkably declined for successive 0.6 PV of air injection. From the CT images of air injection into the fractured shale cores, air injection has the potential to recover incremental oil in the presence of fractures.