Lean gas Huff and Puff process for Eagle Ford Shale: Methane adsorption and gas trapping effects on EOR

Abstract

In order to improve the current recovery factor of unconventional reservoirs and take it to the next level (10–20%), gas Huff and Puff is a very promising enhanced oil recovery technology used currently. Many laboratory works and field pilot tests have been conducted recently. However, most of the research work is based on CO2 as an injected gas. Few of them were built upon the more realistic lean gas Huff and Puff process. From the feedback of lean gas Huff and Puff pilot in Eagle Ford, the field response is always beyond analysis and reservoir simulation forecast. Methane, the main component of lean gas, and its adsorption and desorption effects on the unconventional resources are pronounced due to nanopore confinement effects and a much larger surface area than conventional reservoirs. On the other hand, the minimum miscibility pressure of lean gas in Eagle Ford is high (>4000 psi), which makes gas phase and liquid phase still separate in a long period of Huff and Puff process before reservoir pressure is elevated high enough to developing the supercritical state. Therefore, relative permeability hysteresis – gas trapping effect in nature, should be also very significant on gas EOR performance for unconventional resources. To our best knowledge, there are no such studies about the lean gas adsorption and gas trapping for Huff and Puff process of unconventional reservoir reported so far. In this study, these two mechanisms are systematically analyzed and quantified in a compositional reservoir simulation study. The gas EOR dependence on permeability is also studied and the resulting gas injectivity problem is answered, trying to explore the real problem encountered in the pilot practice.