(236c) 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 Eagle Ford core samples were used for each group. One group were saturated with Soltrol 130 refined 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 efficiency by measuring the weight difference of a core sample before and after the huff-n-puff process, the core was imaged using X-ray CT to visualize the phase flow and fluid distribution inside the core. It is the first time to compare the RF results from shale core samples saturated with refined oil and crude oil by using 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 accumulative recovery factor of core samples after each cycle. The CT images of samples were generated at various recovery process that core samples were scanned in the slice thickness of 1.25 mm under the conditions of dry, fully oil-saturated as well as during the huff-n-puff process. The results show that recovery factor of samples saturated with refined 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 refined oil is produced under 3 hours soaking time compare with 1 hour soaking time with other operation parameters being the same, while the rule is not fit for the case of cores saturated with crude oil. Other factors that need to be investigated may cause such consequence. So the RF is sensitive with oil properties.