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Currently, about 50% of US oil production comes from unconventional basins, where only around 10% of the mobile oil is recovered. Advanced technologies, such as gas EOR, are essential to significantly increase recovery and improve economic viability. Much of the work on EOR for unconventionals has focused on gas injection methods. We thoroughly reviewed the current understanding of gas Huff-n-Puff (HnP) technologies and found a lack of evaluation criteria for the success of HnP gas injection and its potential risks. We formed a team of geologists, petroleum engineers, geoscientists, and field operators to conduct a field gas-EOR pilot test. This study aims to develop a criteria-based assessment workflow that combines laboratory simulation, reservoir modeling, and field pilot testing. Our plan for creating a gas HnP workflow includes three objectives: 1) to investigate new injectants that improve miscibility and sweep efficiency, 2) to identify optimal conditions for Huff-n-Puff injection, and 3) to trace oil contributions from the matrix versus the fractures during production.
A custom-built high-pressure and high-temperature gas adsorption apparatus enables us to simulate gas Huff-n-Puff injection. The gas intake experiment was conducted on 3/8” core plugs at high temperature. The process involves three steps: re-saturation of the core plugs with gas (up to 15,000 psia, rapid release of gas from the chamber, and degassing of the core plugs. The apparatus can evaluate the effect of lithology and lithofacies on gas EOR.
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