Maximizing Geothermal Energy Recovery from Enhanced Geothermal Systems Through Huff-And-Puff: A Comprehensive Simulation Study
Authors: Sekar Lokesh Kumar , Okoroafor Esuru. R. 
Published: August 2024

ABSTRACT:
The huff-and-puff technique, originally developed for cyclic single well operations in low-permeability sedimentary reservoirs, has shown promise for improving oil recovery. This approach is particularly relevant in tight reservoirs where conventional multi-well patterns face challenges due to extremely poor permeability. The technique involves cyclic injection of various fluids like steam, solvents, surfactants, or their combinations to enhance the recovery process. This study extends the application of the huff-and-puff technique to deep, tight Enhanced Geothermal Systems (EGS) with the aim of harnessing geothermal energy. Leveraging a sophisticated thermohydromechanical model, a key scenario is investigated: which is optimizing huff-and-puff cycle durations. The results demonstrate that substantial enhancements in geothermal system performance can be achieved by fine-tuning the heat farming strategy through strategic adjustments in injection and soak times. While this method may not provide continuous geothermal energy, it presents a viable option for heat storage and direct utilization. These insights represent a significant step towards the more efficient exploitation of geothermal resources, ultimately enhancing the overall energy recovery process in tight EGS reservoirs. This research opens avenues for broader applications of the huff-and-puff technique in geothermal energy production and promotes sustainable energy solutions in challenging subsurface environments.

1. INTRODUCTION
Geothermal Energy involves harnessing heat beneath the Earth's surface to generate electricity. The process involves drilling wells to access geothermal reservoirs and using steam or hot water to drive turbines and produce electricity (Bagher et al., 2014). Flexible energy resources are key for a reliable power supply in a decarbonized grid with a significant fraction of variable power sources (Cruz et al., 2018). Geothermal energy has always been an economic resource for baseload power and district heating (Kyriakis & Younger, 2016). Recently, geothermal facilities have been expanding beyond baseload to supply flexible heat and electricity (Aljubran & Horne, 2024). The major challenge associated with geothermal energy tapping is its reduced thermal performance over time (Abbas et al., 2014). To reduce dependency on naturally occurring geothermal reservoirs and to increase the contact area in low permeability reservoirs, Enhanced Geothermal Systems (EGS) are introduced. EGS involves creating an artificial reservoir by stimulating the natural permeability of hot rock formations beneath the Earth's surface (Lu, 2020). The technology delineates the establishment of a meticulously engineered geothermal reservoir within hot, often crystalline rock through the utilization of reservoir stimulation methodologies. Subsequently, water circulation is employed within this engineered reservoir to harness thermal energy from the heated rock (Duchane & Brown, 2000).