Course Content

Well Drilling and Hydraulic Stimulation

Energy is a Hot Topic Environmental Considerations for Geothermal Energy Well Drilling and Hydraulic Stimulation

The exploration and drilling phases of geothermal projects have specific environmental concerns that are distinct from the operational phases of these projects. Potential exploration and development concerns may include water (for example, water quantity use, groundwater contamination, disposal, and remediation), induced seismicity, and land subsidence caused mainly by fluid withdrawal. Let’s take a look at each of these concerns, starting with the drilling phase.¹

Techniques and approaches used for drilling wells are almost identical whether the wells are for a geothermal or oil and gas program. Some variations may occur, depending upon the particular geothermal concept. Well drilling requires water and (commonly) some type of bentonite-rich additive that increases viscosity enough to return drill cuttings to the surface.² To find out more about drilling engineering and technology, you can visit our course “In Pursuit of the Safe Well”.

An electric drilling rig with associated pipe in the DJ Basin, Colorado — An electric drilling rig with associated pipe at a wellsite in the Denver-Julesburg Basin (DJ Basin) east of the Rocky Mountains in Colorado. This rig is drilling an oil and gas well for the operator, Civitas. Drilling operations for geothermal projects would be quite similar to those for oil and gas projects.

Whether the application is geothermal or oil and gas, drilling processes require a number of necessary environmental considerations, for example, identifying a water source with sufficient volumes, managing fluids with potentially dissolved contaminants or cuttings, and ensuring that local groundwater resources are not impacted by the drilling and completion processes.³ The oil and gas industry has decades of experience in addressing these environmental considerations related to drilling, and state regulatory agencies have numerous rules and inspectors in place to oversee these operations. However, if geothermal programs increase in number to the scale of the oil and gas industry, clearly large numbers of personnel will be needed for the geothermal workforce of the future.

Water and Fluid Management

According to the U.S. Energy Information Agency, nearly 1,000,000 oil and gas production wells are in operation today, and many more have been drilled over the last 100 years, each of these wells required water for drilling.⁴

Experience from Oil and Gas Wells

A more recent history of horizontal drilling indicates that the volume of water used for drilling and cementing oil and gas wells is about 380,000 gallons per well.⁵ If the well were to require hydraulic stimulation, then the volume needed could increase tenfold to create an adequate fracture network. These water-use numbers have increased with time because subsurface engineering in the form of horizontal wells have increased in length, and now approach 10,000 feet (1.9 miles or three kilometers) or longer.⁶ And depending on the region of the country (more humid East Coast versus drier Southwest), water may be more or less plentiful and/or readily available.

True or False: Drilling an EGS well will be a new venture, and we do not fully understand the technology nor environmental considerations related to drilling.

True

Incorrect

There are currently about 1,000,000 oil and gas wells in production in the United States. This experience with both the technology and environmental considerations can be immediately applied to any EGS well projects.

False

Correct

Geothermal Wells

Wells drilled for geothermal energy production would need to identify and source similar volumes of water, especially for Enhanced Geothermal Systems, which also may use a form of hydraulic fracturing. In nearly all cases, wells drilled to substantial depths require fluids augmented with bentonite or other additives that increase viscosity to entrain cuttings, cool the drilling bit and pipe, and maintain borehole stability.⁷

Depending on bottom-hole temperature, fluids and cuttings that return to the surface from a hot reservoir need to be cooled before being recirculated downhole. In some cases, long-term exposure to elevated temperatures greater than 150°C (302°F) could increase the viscosity of bentonite, potentially clogging pipes, and leading to degraded circulation. Use of high temperature resistant polymers could reduce this potential. Regardless of the technology, the potential for local impacts requires careful analyses using location specific data and information.⁸ A one-size model will not fit when examining local environmental considerations.

Since around 2005, a combination of directional drilling and hydraulic fracturing (also known as frac’ing) has become a game changer in oil and gas exploration and development. Not surprisingly, the practice has undergone significant innovation and improvement in the nearly 20 years since widespread use began, including a new understanding of the chemical additives used in the process. In general, frac fluids are dominated by water and proppants (particles used to wedge open fractures), often sand, but sometimes mixed with chemicals to inhibit corrosion and scaling, reduce friction along the inside of the drilling pipe, and reduce biological buildup. The FracFocus Chemical Disclosure Registry⁹, managed by the Ground Water Protection Council and Interstate Oil and Gas Compact Commission, has become an important tool for governments, industry, and the general public to obtain information on fracturing fluid chemistry. Although not all chemical concentrations are disclosed due to intellectual property concerns, the Registry is a significant step forward in transparency.¹⁰

Image Credits

Electric-drilling-rig-DJ-Basin-25%: photo courtesy Hilary Olson

Oklahoma Academic Standards

Environmental Science: 3.1, 3.2, 3.3, 3.4, LS2.7
Earth and Space Science: 3.1, 3.2, 3.5
Physical Science: PS3.1, PS3.2, PS3.3, PS3.4

TEKS Standards

Earth Systems Science: 1.A, 1.D, 2.D, 3.B, 4.B, 4.C, 9.B, 9.D, 12.E, 13.A, 13.B
Environmental Systems: 1.A, 1.D, 3.B, 4.C, 6.B, 6.C, 6.E, 6.F, 10.A, 12.A, 12.B, 12.C

College Board Units and Topics

AP Environmental Science: 5.9, 6.1, 6.3, 6.4, 6.10, 8.1, 8.2

Next Generation Science Standards

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