Underbalanced Geothermal Drilling

Geothermal energy is defined as stored thermal energy underneath the surface of the Earth in the form of heat that radiates from the center of our planet. This heat originates some 4,000 miles down at the Earth’s inner core at temperatures that are estimated to be from 9,000 to 13,000 degrees Fahrenheit. Magma, or molten rock, is formed due to high temperature and pressure in the mantle and crust. It then migrates upwards due to its reduced density and when structural zones allow for movement. This magma then heats rock and trapped water beneath the surface of the Earth’s crust to temperatures up to 700 degrees Fahrenheit. Some of this hot water makes its way to the surface in the form of "hot springs" or "geysers", but most of it stays trapped underground in fractures and porous rock. This accumulation of hot water is better known as "geothermal reservoirs."

Geothermal power is a clean, reliable and renewable resource that currently provides energy to the USA and over 20 countries around the world. It’s viewed as a renewable energy resource because the heat radiating from the Earth’s core is essentially limitless. As of now, the United States leads the world in geothermal electricity production of 3,000 MW of online availability from 77 power plants. The Philippines follow in at second place with 1,900 MW of online availability. As opposed to other renewable energy sources such as wind power, geothermal energy is not dependent upon the changing weather conditions. In addition, geothermal power has the ability to greatly reduce global warming resulting from its relatively low emissions compared with other nonrenewable energy sources.

In order to generate electricity from geothermal resources, geothermal wells must be drilled to produce the steam or hot water from the reservoir. Depending on the site, the wells can range in depth from approximately 5,000 feet to 20,000 feet. These wells carry the geothermal fluids and steam up to the surface. Multiple producing wells are connected together and then ultimately reach a power plant, where steam is then converted into electricity.

While drilling these wells, one of the biggest problems is that lost circulation is almost always encountered. The reason for this is because geothermal reservoirs are relatively low in pressure and cannot support a column of fluid. As a result, cuttings are not removed easily from the well bore and can cause pipe sticking. With complete loss of returns, drilling mud must be mixed and pumped at high enough rates to keep the bit clean, which can be a very expensive process.

Omni Compressed Air, Ltd. can help eliminate these problems by using underbalanced drilling techniques to circulate the well and remove cuttings. Rates of penetration are also greatly increased (3-5 times) when air drilling so the well is drilled in fewer days, thus saving money. Another benefit is that air drilling provides good formation samples and can give accurate estimates of geothermal fluid production.