Evaluation of cyclic gas injection eor performance on shale core samples using x-ray CT scanner

Production from tight and shale oil reservoirs will be more global in the coming decades. In order to efficiently produce unconventional reservoirs in a huff-n-puff injection mode, it is necessary to have a deeper understanding of the oil recovery mechanism. In this study, such potential is investigated by using CT imaging technique. It helps us to observe the process of oil production from the core samples and evaluate the recovery performance based on CT images. Two groups of experiments were conducted, and two Wolfcamp core samples were used for each group. One group were saturated with mineral oil, the other one were saturated with crude oil. All samples were experienced 10 cycles of huff-n-puff N2 injection to recovery oil. The only variable parameter in each group was the soaking period that were 1 hour and 3 hours, respectively. In addition to determining recovery factor by measuring the core weight loss for each cycle, the core was imaged using X-ray CT to visualize the phase flow and fluid distribution inside the core. This study compared the RF results from shale core samples saturated with mineral oil and crude oil by cyclic gas injection EOR method. The work also introduced CT imaging during the experiment to assist us to understand the oil displacement process. This study presents experimental results of cumulative recovery factor of core samples after each cycle. Samples were imaged at various recovery process of huff-n-puff. The results show that recovery factor of samples saturated with mineral oil under the soaking period of 3 hours and 1 hour are 32.9% and 24.1%, respectively. The recovery factor (RF) of samples saturated with crude oil under 3 hours and 1 hour soaking period are 23.7% and 27.9%. The obtained CT images, together with the analysis of CT number at various locations of the sample during the experiment reveal the density and composition of substance inside the plug and reflect the oil recovery. Results show that more mineral oil is produced under 3 hours soaking time compare with 1 hour soaking time with other operation parameters being the same, while the results are not the same for the case of cores saturated with crude oil. The difference in properties of core samples is believed to cause such consequence. So the RF is sensitive to rock and oil properties.