**5. Conclusions**

Figure 7 shows the pressure, stress and stress level evolution for the well block in the caprock for the thermal and isothermal model. In the isothermal model, due to the low permeability of caprock, pressure increase in caprock is negligible compared to the reservoir, and stress level remains low. However as seen in Figure 8 (which shows the stress, pressure and temperature variation of the well block in the caprock during the first 10 years of injection), the first caprock layer is quickly pressurized, and later its temperature also decreases due to heat transfer. Stress level is rapidly increasing with time due to thermally induced decrease of total stresses. Therefore the chance of failing the rock in shear for the caprock is higher for the

0 5 10 15 20 25 30

Pressure(Isothermal) Pressure(Thermal)

Minimum Stress(Isothermal) Minimum Stress(Thermal) Stress Level(Isothermal) Stress Level(Thermal)

**Time(yr)**

**Figure 7.** pressure, minimum total stress, and stress level for the thermal and isothermal model for the well block in

The changes inthe stress level correspondto themovement oftheMohr circle withtime. Shortly after injection (0.1 days), the stress circle moves to the right due to the slight growth of total stresses. This is a poroelastic effect which is a result of early time-increase of the block pres‐ sure in the caprock. This can be clearly seen in Figure 8. However, as soon as the block temper‐ ature is lowered due to thermal diffusion (conduction), thermoelasticity dominates and total minimum stress reduces (Figure 8) and stress circle moves to the left toward the failure cone.

The mechanism shown here is somewhat exaggerated because of the upstream numerical treatment of the fracture transmissibility between the blocks, but the relative comparison is valid. Accurate modeling would require very fine vertical grid at the reservoir-caprock interface or the development of more sophisticated numerical technique. These aspects are

0.5

0.55

0.6

0.65

**Stress level**

0.7

0.75

thermal model compared to isothermal model.

24000

the immediate caprock layer

being currently studied.

29000

34000

39000

**Pressure,Minimum stress(kPa)**

44000

49000

954 Effective and Sustainable Hydraulic Fracturing

This paper studies thermo-elastic and poro-elastic response of the reservoir and caprock to increasing of pressure and reduction of temperature after CO2 injection and the resulting consequences for the possibility of reaching tensile or shear failure both for the injection below and above reservoir's fracture pressure.

When injecting a fluid below isothermal fracture pressure with a temperature below reservoir temperature, the fracture pressure will decrease and minimum effective stress in the reservoir may reduce below zero for the fracturing to initiate and propagate in the reservoir.

Our results show that the reduction of the minimum effective stress due to thermal effects is larger for the lower reservoir layers. Therefore in case of dynamic fracture propagation, fracture growth would be larger for the lower reservoir layers due to larger cooling for these layers.

Thermal effects of injection with cold CO2 may also create the possibility of shear failure in the caprock.

#### **Author details**

Somayeh Goodarzi1\*, Antonin Settari1 , Mark Zoback2 and David W. Keith3

\*Address all correspondence to: sgoodarz@ucalgary.ca

1 University of Calgary, Calgary, Canada

2 Stanford University, USA

3 Harvard University, USA

#### **References**

[1] Solomon, S. Carbon Dioxide Storage: Geological Security and Environmental Issues-Case Study on the Sleipner Gas Field in Norway. The Bellona Foundation. (2006).

[9] Gupta, N. (2008). The Ohio river valley CO2 storage project, Final Technical Report, prepared for US Department of Energy-National Energy Technology Laboratory [10] Van Genuchten, M. T. equation for predicting the hydraulic conductivity of unsatu‐

Thermal Effects on Shear Fracturing and Injectivity During CO2 Storage

http://dx.doi.org/10.5772/56311

957

[11] Collieu, A. McB., Powney, D. J., Girifalco, L. A. et al., (1975). The Mechanical and Thermal Properties of Materials and Statistical Physics of Materials. Phys. Today 28,

[12] Fjaer, E, Holt, R. M, Horsrud, P, et al. (2008). Petroleum Related Rock Mechanics. 441.

[13] Guildner, L. A. (1958). The thermal conductivity of carbon dioxide in the region of the critical point, Proceedings of the National Academy of Sciences of the United

[14] Yaws, C. (2008). Thermophysical properties of chemicals and hydrocarbons. 793. Wil‐

[15] Sneddon, I. N, & Lowengrub, M. Crack Problems in the Classical Theory of Elastici‐

[16] Goodarzi, S, Settari, A, & Keith, D. (2012). Geomechanical modeling for CO2 storage in Nisku aquifer in Wabamun lake area in Canada. International Journal of Green‐

[17] Maurer, W. C. (1965). Bit-Tooth Penetration under Simulated Borehole Conditions,

rated soils: Soil Science Society of America Journal, , 44, 892-898.

51

Elsevier.

States of America, , 44(11), 1149-1153.

ty, John Wiley & Sons Inc., New York, (1969). , 19.

liam Andrew Publishing

house Gas Control , 10, 113-122.

Petroleum Transactions


[9] Gupta, N. (2008). The Ohio river valley CO2 storage project, Final Technical Report, prepared for US Department of Energy-National Energy Technology Laboratory

**Author details**

Somayeh Goodarzi1\*, Antonin Settari1

956 Effective and Sustainable Hydraulic Fracturing

1 University of Calgary, Calgary, Canada

Technology Conference

ogists. , 18(3), 1-20.

GHG).

139706.

2 Stanford University, USA

3 Harvard University, USA

**References**

\*Address all correspondence to: sgoodarz@ucalgary.ca

Fuel Processing Technology. (2005). , 86, 1547-1568.

, Mark Zoback2

[1] Solomon, S. Carbon Dioxide Storage: Geological Security and Environmental Issues-Case Study on the Sleipner Gas Field in Norway. The Bellona Foundation. (2006).

[2] Preston, C, Monea, M, et al. IEA GHG Weyburn CO2 Monitoring and Storage Project,

[3] Wright, L. W. (2007). The In Salah Gas CO2 Storage Project. International Petroleum

[4] QuintessaNational Institute of Advanced Industrial Science and Technology of Ja‐ pan, Quintessa Japan, JGC Corporation, Mizuho Information and Research Institute. (2007). Building Confidence in Geological Storage of Carbon Dioxide. Ministry of Economy, Trade and Industry (METI), IEA Greenhouse Gas R&D Programme (IEA

[5] Goodarzi, S, Settari, A, Zoback, M, & Keith, D. A Coupled Geomechanical Reservoir Simulation analysis of CO2 storage in a Saline Aquifer in the Ohio River Valley. (2011). Environmental Geosciences journal. American Association of Petroleum Geol‐

[6] Goodarzi, S, Settari, A, Zoback, M, & Keith, D. Thermal Aspects of Geomechanics and Induced Fracturing in CO2 Injection With Application to CO2 Sequestration in Ohio River Valley. SPE-PP, SPE International Conference on CO2 Capture, Storage, and Utilization held in New Orleans, Louisiana, USA, 10-12 November (2010). ,

[7] Zoback, M. D, & Zoback, M. L. State of stress and intraplate earthquakes in the cen‐

[8] Lucier, A, Zoback, M, Gupta, N, & Ramakrishnan, T. S. (2006). Geomechanical as‐ pects of CO2 sequestration in a deep saline reservoir in the Ohio River Valley region.

tral and eastern United States. Science, (1981). , 213, 96-109.

Environmental Geosciences 13 (2), 85-103.

and David W. Keith3


**Chapter 49**

**Scale Model Simulation of Hydraulic**

**Fracturing for EGS Reservoir Creation**

Luke Frash, Marte Gutierrez and Jesse Hampton

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/56113

**Abstract**

**Using a Heated True-Triaxial Apparatus**

Geothermal energy technology has successfully provided a means of generating stable base load electricity for many years. However, implementation has been spatially limited to rare high quality traditional resources possessing the combination of a shallow high heat flow anomaly and an aquifer with sufficient permeability and fluid recharge. Enhanced Geother‐ mal Systems (EGS) technology has been proposed as a potential solution to enable addition‐ al energy production from the much more common non-traditional resources. To advance this technology development, a heated true triaxial load cell with a high pressure fluid injec‐ tion system has been developed to simulate an EGS system from stimulation to production. This apparatus is capable of loading a 30x30x30 cm3 rock sample with independent princi‐ pal stresses up to 13 MPa while simultaneously providing heating up to 180 ºC. Multiple ori‐ entated boreholes of 5 to 10 mm diameter may be drilled into the sample while at reservoir conditions. This allows for simulation of borehole damage as well as injector-producer schemes. Dual 70 MPa syringe pumps set to flow rates between 10 nL/min and 60 mL/min injecting into a partially cased borehole allow for fully contained fracturing treatments. A six sensor acoustic emission (AE) array is used for geometric fracture location estimation during intercept borehole drilling operations. Hydraulic pressure sensors and a thermocouple array allow for additional monitoring and data collection as relevant to computer model valida‐ tion as well as field test comparisons. The results of the scale model hydraulic fracturing tests demonstrate the functionality of the equipment while also providing some novel data on the propagation and flow characteristics of hydraulic fractures. Fully characterized test sample materials used in the scale model tests include generic cement grout, custom high

> © 2013 Frash et al.; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

> © 2013 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,

distribution, and reproduction in any medium, provided the original work is properly cited.

and reproduction in any medium, provided the original work is properly cited.
