(659l) Experimental Evaluation of Asphaltene Deposition-Associated Damage and Oil Recovery from Shale Cores By Cyclic Nitrogen Injection

Production from unconventional reservoirs using gas enhanced oil recovery has gained much attention due to its ability to increase oil recovery to high percentages. Gas Enhanced Oil Recovery (GEOR) is one of the most applied EOR methods to increase oil recovery. Asphaltene precipitation and deposition during nitrogen injection to displace oil are major problems during production. This research investigates the effect of using immiscible cyclic nitrogen injection on oil recovery and asphaltene pore plugging using Eagle Ford shale cores.

Methodology

The minimum miscibility pressure of nitrogen was determined using a slim tube. Eagle Ford shale cores were fully saturated with 19 cp viscosity crude oil. A high-pressure vessel was used to accommodate the core during the cyclic pressure. Different soaking immiscible pressures (500, 750, and 1000 psi) were used to study the effect on the oil recovery when using immiscible pressure. Also, Various soaking times (6, 12, 24 hours) were selected to investigate the effect of soaking time. Finally, the number of cycles (1, 2, 3, 4, and 5) and production times (30, 60 minutes) were investigated to identify the impact of cycles injection pressure. SEM analysis used to investigate the pore plugging by asphaltene.

Results

The MMP was determined to be 1600 psi from the slim-tube test. Results showed that as the number of cycles increased, RF also increased, and this increase depended on different parameters (e.g., soaking time). The RF achieved after conducting three cycles of nitrogen injection was 35.33%, 7.14% higher than RF after performing five cycles of nitrogen injection. The results revealed that the efficacy of high nitrogen injecting to produce oil from the core samples is higher than lower pressures at the same operating parameters. The higher pressure, the higher recovery factor in all experiments. The SEM analysis showed that the asphaltene plugged the pores of the cores significantly. Although higher huff pressure causes more reduction in oil recovery by asphaltene deposition, the oil recovery by higher pressure is still higher.

Novel Information

This research investigates asphaltene deposition and its impact on oil recovery during nitrogen huff-n-puff injection. This research will help highlight the severity of asphaltene damage, especially in nano pores, mainly present in unconventional reservoirs. By studying the impact of different factors on asphaltene formation damage during nitrogen injection, asphaltene deposition may be avoided in future applications.