< Back to Calendar


September 16th, 2020 12:00 PM - 1:00 PM

Evaluation of the Factors Controlling EOR in Unconventional Shale Reservoirs

Ali Tinni

Mewbourne School of Petroleum and Geological Engineering

University of Oklahoma

Norman, OK

Link to register:


Hydrocarbon production from unconventional shale reservoirs is characterized by steep production decline and primary production recovery factors lower than 15%. To sustain their production, operators are increasingly relying on Huff-n-Puff enhanced oil recovery (EOR). However, the implementation of Huff-n-Puff EOR in shales requires a good understanding of how the injection gas will react with the remaining hydrocarbon and how the reservoir properties will affect the EOR process. We will present a workflow that involves the use of crushed rock material to evaluate how operational parameters and reservoir properties affect Huff-n-Puff EOR in the Eagle Ford, Wolfcamp, Duvernay and Montney shales.  

Huff-n-Puff experiments were completed on crushed rock samples (7 to 8 mm particle size) using gases with variable proportions of ethane and methane at injection pressures varying from 1000 psi lower than the minimum miscibility pressure (MMP) to 1000 psi larger than the MMP. The impact of soaking time was investigated by conducting Huff-n-Puff experiments with soaking times varying from 1 hour to 6 hours.

Our investigation shows that the maximum recovery factor from Huff-n-Puff EOR in shales is controlled by the total organic content (TOC) of the reservoir. As TOC increases, the maximum recovery factor reduces. Enrichment of the injection gas with ethane increases the efficiency of the EOR process. The results of this experimental program also show that soaking and injection times can be combined into a single variable we call residence time. Injection pressure relative to the minimum miscibility pressure exerts a primary control on the amount and type of hydrocarbon produced from Huff-n-Puff. At pressures lower than the minimum miscibility pressure only hydrocarbon components lighter than octadecane (C 18) are producible while at pressures greater than the minimum miscibility pressure, hydrocarbon fractions up to tetracosane (C 24) are producible.


Ali Tinni is a faculty in the Petroleum Engineering Department of the University of Oklahoma. His current research interests include fluid flow and storage as well as EOR in unconventional reservoirs. He holds Master’s and PhD degree in Petroleum Engineering from the University of Oklahoma.