Abstract

We are developing swellable Preformed Particle Gels (PPG), which can control preferential fluid and heat flow through fracture networks to increase the performance of EGS reservoirs. Part of this development is a mathematical model and numerical simulator to simulate PPG treatments by considering coupled thermal-hydraulic-mechanical effects, and gel swelling kinetics and plugging efficiency, from which an optimized gel treatment design and operation can be achieved. The starting point for our mathematical model is the TOUGH2-CSM formulation and code. The TOUGH2-CSM fluid and heat flow formulation is based on the TOUGH2 one for multiphase, multicomponent, and multi-porosity systems, with the latter including the MINC and EDFM models. We modified our formulation to simulate injection of PPG into fractures. We developed an equation of state module for gel-water systems based on a previous TOUGH2 module that handles air and water since PPGs consist mostly of water. We used experimental studies of PPG flow through fractures to obtain the PPG flow formulation, formulating PPG flow as that of a shear-thinning fluid with a yield stress (Herschel-Bulkley fluid). Injected PPG consists of polymer-based particles that are swollen with water. When injected into a fracture whose walls are permeable, it was found that water leaks off through the fracture walls and a more concentrated PPG is deposited there as a filter cake. In addition, the transverse pressure gradient under which PPG flows can also dehydrate the PPG, resulting in a more concentrated, flowing PPG and a separate flowing water phase. These features of PPG were also incorporated into our model, as well as the ability of PPG to swell over time. Our simulator's features were verified by matching data from experimental studies. They include PPG injection into open fractures, which were used to verify our PPG rheology and longitudinal dehydration models, and PPG injection into a closed fracture, which were used to verify our transverse dehydration model. We then applied our model to a two-fracture case to demonstrate the ability of the formulations to simulate PPG blockage of highly conducting fractures, and finally applied it to a synthetic EGS to ascertain the effect of blocking these highly conductive fractures on energy production.

Department(s)

Geosciences and Geological and Petroleum Engineering

Publication Status

Available Access

Comments

Office of Energy Efficiency and Renewable Energy, Grant DE-EE0009790

International Standard Book Number (ISBN)

978-195902558-0

International Standard Serial Number (ISSN)

2689-5382; 2689-5366

Document Type

Article - Conference proceedings

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2025 Society of Petroleum Engineers, All rights reserved.

Publication Date

01 Jan 2025

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