Recovery mechanisms and relative permeability for oil/gas system at near-miscible conditions: effects of immobile water saturation, wettability, hysteresis and permeability

Seyyed Mobeen Fatemi, Mehran Sedah Sohrabi, Shaun Ireland, Mahmoud Jamiolahmady

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

Near-miscible gas injection represents a number of processes of great importance to reservoir engineers including hydrocarbon gas injection and CO2 flood. Very little experimental data is available in the literature on displacements involving very low-IFT (interfacial tension). In this paper, we present the results of a series of two-phase and three-phase gas injection (drainage) and oil injection (imbibition) core flood experiments for an gas/oil system at near-miscible (IFT= 0.04 mN.m-1) conditions. Two different cores; a high-permeability (1000 mD) and a lower permeability (65 mD) core were used in the experiments and both water-wet and mixed-wet conditions were examined.

The results show that despite a very low gas-oil IFT, there is significant hysteresis between the imbibition and drainage oil and gas relative permeabilities (kr) curves in the 65mD core. Hysteresis was less for 1000mD core (compared to the 65 mD core) but it still could not be ignored. Near-miscible kr hysteresis was significant for both water-wet and mixed-wet systems. Presence of immobile water in the water-wet cores improved oil relative permeabilities but reduced gas relative permeabilities in both imbibition and drainage directions. As a result, oil recovery for gas injection experiments improved when the rock contained immobile water. Both oil and gas relative permeabilities reduced when the rock wettability was altered to mixed wet from water wet and as a result, oil recovery by gas injection in the mixed-wet rock was less than that obtained under water-wet conditions. We offer explanations for these observations based on our understanding of the pore-scale interactions and mechanisms, the distribution of fluid phases and their spreading bahaviour.

The results help us better understand the impact of some of the important parameters pertinent to kr and its hysteresis especially in very low IFT gas-oil systems and mixed-wet rocks. Understanding these effects and behavior is important for improved prediction of the performance of gas injection and water-alternating gas (WAG) injection in oil reservoirs.
Original languageEnglish
Title of host publication18th SPE Improved Oil Recovery Symposium
Subtitle of host publication14-18 April 2012, Tulsa, Oklahoma, USA
PublisherSociety of Petroleum Engineers
Number of pages28
ISBN (Print)978113991978
DOIs
Publication statusPublished - Apr 2012
Event18th SPE Improved Oil Recovery Symposium 2012 - Tulsa, Oklahoma, United States
Duration: 14 Apr 201218 Apr 2012

Conference

Conference18th SPE Improved Oil Recovery Symposium 2012
CountryUnited States
CityTulsa, Oklahoma
Period14/04/1218/04/12

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    Fatemi, S. M., Sohrabi, M. S., Ireland, S., & Jamiolahmady, M. (2012). Recovery mechanisms and relative permeability for oil/gas system at near-miscible conditions: effects of immobile water saturation, wettability, hysteresis and permeability. In 18th SPE Improved Oil Recovery Symposium: 14-18 April 2012, Tulsa, Oklahoma, USA [SPE-154277-MS] Society of Petroleum Engineers. https://doi.org/10.2118/154277-MS