Laboratory Visualization of Enhanced Gas Recovery in Shale
- Youssef Elkady (Energy Resources Engineering, Stanford University) | Anthony Kovscek (Energy Resources Engineering, Stanford University)
- Document ID
- Society of Petroleum Engineers
- SPE Annual Technical Conference and Exhibition, 26-29 October, Virtual
- Publication Date
- Document Type
- Conference Paper
- 2020. Society of Petroleum Engineers
- 1.6 Drilling Operations, 1.6.9 Coring, Fishing
- enhanced recovery, unconventionals, shale, laboratory studies, nondestructive imaging
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In this work, we lay the experimental groundwork for measuring CO2 storage, and other industry-relevant gases, in shale on a core scale. This works emphasizes the role of adsorption on gas storage using two core samples (one Eagle Ford and one Wolfcamp). Mass balance and Computed Tomography (CT) methods are used independently to co-validate our results. The validation process allows for confidence in the accuracy of the CT visualizations. In addition, the CT method significantly reduces the characterization time needed for measuring gas storage before running any further investigations related to gas flow and recovery.
The pulse-decay technique is initially used to quantify apparent porosity, permeability, and adsorption for He, N2, Kr, CH4, and CO2 at room temperature (and 42 °C in some cases) up to 800 psia pore pressure. In the case of Kr, Eagle Ford core (EF1) is imaged at the end of each pressure pulse step to compare CT-derived to pulse decay derived results. At 650 psia, CO2 and Kr storativity (SCF of gas per ton of rock) in sample EF1 have roughly 4.5× and 2× the storativity of He, respectively. Absolute adsorption of CO2 (181 SCF/Ton) is significantly greater than N2 (5 SCF/Ton) and Kr (45 SCF/Ton) at 650 psia pore pressure. Furthermore, our proposed CT approach yields a good match to the mass balance characterization results for Kr as opposed to the conventional CT formulation.
Permeability results show negative correlation between adsorption affinity of gas and sample liquid-like permeability. In the case of Kr and N2 measurements on sample EF1, the greater compressibility of Kr is overcome by its larger adsorption affinity resulting in a greater than N2 permeability at lower pore pressures but lower permeability at higher pore pressures. The Wolfcamp sample (WC2) captures a potentially irreversible effect of CO2 on permeability attributed to either permanent matrix swelling or matrix softening.
This study bridges both CT and mass balance derived results to ensure accurate visualization of the physics during characterization. Both methods show a better displacement of in-situ Kr (proxy for CH4) with CO2 as compared to N2 injection. CT visualizations of both gas displacement experiments show two relatively permeable flow pathways emerge during early times.
|File Size||1 MB||Number of Pages||22|
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