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Title: Environmentally Friendly, Rheoreversible, Hydraulic-fracturing Fluids for Enhanced Geothermal Systems

Abstract

Cost-effective creation of high-permeability reservoirs inside deep crystalline bedrock is the primary challenge for the feasibility of enhanced geothermal systems (EGS). Current reservoir stimulation entails adverse environmental impacts and substantial economic costs due to the utilization of large volumes of water “doped” with chemicals including rheology modifiers, scale and corrosion inhibitors, biocides, friction reducers among others where, typically, little or no information of composition and toxicity is disclosed. An environmentally benign, CO2-activated, rheoreversible fracturing fluid has recently been developed that significantly enhances rock permeability at effective stress significantly lower than current technology. We evaluate the potential of this novel fracturing fluid for application on geothermal sites under different chemical and geomechanical conditions, by performing laboratory-scale fracturing experiments with different rock sources under different confining pressures, temperatures, and pH environments. The results demonstrate that CO2-reactive aqueous solutions of environmentally amenable Polyallylamine (PAA) represent a highly versatile fracturing fluid technology. This fracturing fluid creates/propagates fracture networks through highly impermeable crystalline rock at significantly lower effective stress as compared to control experiments where no PAA was present, and permeability enhancement was significantly increased for PAA compared to conventional hydraulic fracturing controls. This was evident in all experiments, including variable rock source/type, operation pressuremore » and temperature (over the entire range for EGS applications), as well as over a wide range of formation-water pH values. This versatile novel fracturing fluid technology represents a great alternative to industrially available fracturing fluids for cost-effective and competitive geothermal energy production.« less

Authors:
; ; ; ; ; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1222893
Report Number(s):
PNNL-SA-105984
48176
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geothermics, 58:22-31
Country of Publication:
United States
Language:
English
Subject:
Geothermic; fracking; environmental; rheoreversible; Environmental Molecular Sciences Laboratory

Citation Formats

Shao, Hongbo, Kabilan, Senthil, Stephens, Sean A., Suresh, Niraj, Beck, Anthon NR, Varga, Tamas, Martin, Paul F., Kuprat, Andrew P., Jung, Hun Bok, Um, Wooyong, Bonneville, Alain, Heldebrant, David J., Carroll, KC, Moore, Joseph, and Fernandez, Carlos A. Environmentally Friendly, Rheoreversible, Hydraulic-fracturing Fluids for Enhanced Geothermal Systems. United States: N. p., 2015. Web. doi:10.1016/j.geothermics.2015.07.010.
Shao, Hongbo, Kabilan, Senthil, Stephens, Sean A., Suresh, Niraj, Beck, Anthon NR, Varga, Tamas, Martin, Paul F., Kuprat, Andrew P., Jung, Hun Bok, Um, Wooyong, Bonneville, Alain, Heldebrant, David J., Carroll, KC, Moore, Joseph, & Fernandez, Carlos A. Environmentally Friendly, Rheoreversible, Hydraulic-fracturing Fluids for Enhanced Geothermal Systems. United States. doi:10.1016/j.geothermics.2015.07.010.
Shao, Hongbo, Kabilan, Senthil, Stephens, Sean A., Suresh, Niraj, Beck, Anthon NR, Varga, Tamas, Martin, Paul F., Kuprat, Andrew P., Jung, Hun Bok, Um, Wooyong, Bonneville, Alain, Heldebrant, David J., Carroll, KC, Moore, Joseph, and Fernandez, Carlos A. 2015. "Environmentally Friendly, Rheoreversible, Hydraulic-fracturing Fluids for Enhanced Geothermal Systems". United States. doi:10.1016/j.geothermics.2015.07.010.
@article{osti_1222893,
title = {Environmentally Friendly, Rheoreversible, Hydraulic-fracturing Fluids for Enhanced Geothermal Systems},
author = {Shao, Hongbo and Kabilan, Senthil and Stephens, Sean A. and Suresh, Niraj and Beck, Anthon NR and Varga, Tamas and Martin, Paul F. and Kuprat, Andrew P. and Jung, Hun Bok and Um, Wooyong and Bonneville, Alain and Heldebrant, David J. and Carroll, KC and Moore, Joseph and Fernandez, Carlos A.},
abstractNote = {Cost-effective creation of high-permeability reservoirs inside deep crystalline bedrock is the primary challenge for the feasibility of enhanced geothermal systems (EGS). Current reservoir stimulation entails adverse environmental impacts and substantial economic costs due to the utilization of large volumes of water “doped” with chemicals including rheology modifiers, scale and corrosion inhibitors, biocides, friction reducers among others where, typically, little or no information of composition and toxicity is disclosed. An environmentally benign, CO2-activated, rheoreversible fracturing fluid has recently been developed that significantly enhances rock permeability at effective stress significantly lower than current technology. We evaluate the potential of this novel fracturing fluid for application on geothermal sites under different chemical and geomechanical conditions, by performing laboratory-scale fracturing experiments with different rock sources under different confining pressures, temperatures, and pH environments. The results demonstrate that CO2-reactive aqueous solutions of environmentally amenable Polyallylamine (PAA) represent a highly versatile fracturing fluid technology. This fracturing fluid creates/propagates fracture networks through highly impermeable crystalline rock at significantly lower effective stress as compared to control experiments where no PAA was present, and permeability enhancement was significantly increased for PAA compared to conventional hydraulic fracturing controls. This was evident in all experiments, including variable rock source/type, operation pressure and temperature (over the entire range for EGS applications), as well as over a wide range of formation-water pH values. This versatile novel fracturing fluid technology represents a great alternative to industrially available fracturing fluids for cost-effective and competitive geothermal energy production.},
doi = {10.1016/j.geothermics.2015.07.010},
journal = {Geothermics, 58:22-31},
number = ,
volume = ,
place = {United States},
year = 2015,
month = 7
}
  • Abstract The primary challenge for the feasibility of enhanced geothermal systems (EGS) is to cost-effectively create high-permeability reservoirs inside deep crystalline bedrock. Although fracturing fluids are commonly used for oil/gas, standard fracturing methods are not developed or proven for EGS temperatures and pressures. Furthermore, the environmental impacts of currently used fracturing methods are only recently being determined. These authors recently reported an environmentally benign, CO2-activated, rheoreversible fracturing fluid that enhances permeability through fracturing due to in situ volume expansion and gel formation. The potential of this novel fracturing fluid is evaluated in this work towards its application at geothermal sitesmore » under different pH conditions. Laboratory-scale fracturing experiments using Coso Geothermal rock cores under different pH environments were performed followed by X-ray microtomography characterization. The results demonstrate that CO2-reactive aqueous solutions of environmentally amenable polyallylamine (PAA) consistently and reproducibly creates/propagates fracture networks through highly impermeable crystalline rock from Coso EGS sites at considerably lower effective stress as compared to conventional fracturing fluids. In addition, permeability was significantly enhanced in a wide range of formation-water pH values. This effective, and environmentally-friendly fracturing fluid technology represents a potential alternative to conventional fracturing fluids.« less
  • Cost-effective yet safe creation of high-permeability reservoirs within deep bedrock is the primary challenge for the viability of enhanced geothermal systems (EGS) and unconventional oil/gas recovery. Although fracturing fluids are commonly used for oil/gas, standard fracturing methods are not developed or proven for EGS temperatures and pressures. Furthermore, the environmental impacts of currently used fracturing methods are only recently being determined. Widespread concerns about the environmental contamination have resulted in a number of regulations for fracturing fluids advocating for greener fracturing processes. To enable EGS feasibility and lessen environmental impact of reservoir stimulation, an environmentally benign, CO2-activated, rheoreversible fracturing fluidmore » that enhances permeability through fracturing (at significantly lower effective stress than standard fracturing fluids) due to in situ volume expansion and gel formation is investigated herein. The chemical mechanism, stability, phase-change behavior, and rheology for a novel polyallylamine (PAA)-CO2 fracturing fluid was characterized at EGS temperatures and pressures. Hydrogel is formed upon reaction with CO2 and this process is reversible (via CO2 depressurization or solubilizing with a mild acid) allowing removal from the formation and recycling, decreasing environmental impact. Rock obtained from the Coso geothermal field was fractured in laboratory experiments under various EGS temperatures and pressures with comparison to standard fracturing fluids, and the fractures were characterized with imaging, permeability measurement, and flow modeling. This novel fracturing fluid and process may vastly reduce water usage and the environmental impact of fracturing practices and effectively make EGS production and unconventional oil/gas exploitation cost-effective and cleaner.« less
  • We have used an environmentally friendly and recyclable hydraulic fracturing fluid - diluted aqueous solutions of polyallylamine or PAA – for reservoir stimulation in Enhanced Geothermal System (EGS). This fluid undergoes a controlled and large volume expansion with a simultaneous increase in viscosity triggered by CO2 at EGS temperatures. We are presenting here the results of laboratory-scale hydraulic fracturing experiment using the fluid on small cylindrical rock cores (1.59 cm in diameter and 5.08 cm in length) from the Coso geothermal field in California. Rock samples consisted of Mesozoic diorite metamorphosed to greenschist facies. The experiments were conducted on 5more » samples for realistic ranges of pressures (up to 275 bar) and temperatures (up to 210 °C) for both the rock samples and the injected fluid. After fracturing, cores were subjected to a CO2 leakage test, injection of KI solution, and X-ray microtomography (XMT) scanning to examine the formation and distribution of fractures. The design and conduct of these experiments will be presented and discussed in details. Based on the obtained XMT images, Computational Fluid Dynamics (CFD) simulations were then performed to visualize hydraulic fractures and compute the bulk permeability. OpenFOAM (OpenCFD Ltd., Reading, UK), was used to solve the steady state simulation. The flow predictions, based upon the laminar, 3-D, incompressible Navier-Stokes equations for fluid mass and momentum, show the remarkable stimulation of the permeability in the core samples and demonstrate the efficiency of such a CO2 triggered fluid in EGS.« less
  • Success of a hydraulic-fracture treatment depends on selection of the proper fracturing fluid, among other things. This study reviews the evaluation of hydraulic properties of fracturing fluids. Present-day fracturing fluids are classed as Newtonian, polymer solutions, cross-linked polymer solutions, emulsions, micellar solutions, and gelled organic liquids in solution with a liquefied gas. Fracturing fluids exhibit many different forms of time-independent and time-dependent non-Newtonian fluid behavior. New experimental techniques are required in many instances to evaluate these fluids.A fracturing fluid should be compatible with both rock-matrix material and natural fluids contained within matrix pores. Sometimes salt solutions or acidic water basemore » fluids are used to help prevent damage to the rock matrix by clay swelling. In the case of extreme water sensitivity, an oil-base fluid might be used rather than a water-base fluid. (24 refs.)« less