Advanced Characterization and Gas Enhanced Oil Recovery in Tuscaloosa Marine Shale

Abstract This work experimentally determines the viability of enhanced oil recovery (EOR) by gas injection in core samples from Tuscaloosa Marine Shale (TMS) while investigating the effects of gas type, rock dimension, EOR modes and rock brittleness on the EOR performance. TMS is a promising play in Louisiana with estimated reserves of 7 billion barrels of oil. Experimental studies on EOR performance in several shale plays exist but none have been performed to study its viability in TMS. An Eagle Ford sample with dimensions 1.0-inch diameter by 1.0-inch length, TMS cores with dimensions 1.0-inch diameter by 1.0-inch length, 1.0-inch diameter by 2.0-inchlength, and 1.5-inch diameter by 3.0-inch length from 5 wells were used for this study. The cores were cleaned prior to vacuuming and saturation with TMS oil. The coreflood experiments were run at a pressure of 2000 psi and temperature of 70°F. Nitrogen (N2) and carbon dioxide (CO2) were used as injectants for the enhanced oil recovery (EOR) experiments. X-ray Diffraction (XRD) was used to determine the mineralogical content of the TMS core plugs. XRD tests show the fractured cores contain carbonates (5% to 50%) including quartz which makes the rock brittle and more favorable to complex fractures desirable for maximizing recovery in shales, while carbonates are absent in the unfractured cores. Samples E have fractures with higher wt% of quartz and carbonate but lower wt% of clay compared to samples B, C and L. The study shows gas EOR is promising in TMS with CO2 EOR recovery within 22% - 26% compared to N2 EOR recovery within 18% - 19.76%. Gas Assisted Gravity Drainage (GAGD) continuous mode showed higher recovery than GAGD Huff-n-Puff. The ratio of quartz/carbonates to clay in B and C (1.22 - 2.51: 1) was lower compared to the ratio in E (6:1) which explains why B1, B2 and C2 (1.0-in diameter by 2.0-incu length) did not disintegrate prematurely during the experiments compared to E1 with equal dimension. The samples with larger pore volumes, like EL1 (1.5-in diameter by 3.0-in length) displayed more structural integrity than E1(1-in diameter by 2-in length) which disintegrated during its 2nd experiment. This study shows the potential of gas EOR in TMS shale which is insightful as CO2 sequestration has now become increasingly important. It identifies sweet spots for further exploitation and demonstrates the importance of mineralogical content in geomechanical properties in successfully planning EOR experiments. This extends to field applications of EOR. Furthermore, it reveals important findings regarding optimum saturation periods for shale cores in EOR experiments.