Oil and Gas
Colorado is home to 10 of the nation’s 100 largest natural gas fields and three of its 100 largest oil fields. This abundance of resources is due to the geology of the state, which includes the large Niobrara shale formation in northeast Colorado, numerous sedimentary basins throughout the state, and significant deposits of methane-bearing coal in northwest and southern Colorado. The map below is from the Colorado Geological Survey. Detailed information about current oil and gas facilities in the state can be found on the Colorado Oil and Gas Conservation Commission website.
Wells can be drilled vertically or directionally (diagonally) as well as horizontally. In vertical drilling, a borehole between 16–20 inches in diameter is drilled to varying depths below the surface depending on the geology of the formation. Wells in the Raton basin in southern Colorado tend to go only 2,500 ft. underground, while wells in the Piceance basin in western Colorado can be found as deep as 12,500 ft. Horizontal wells involve drilling vertically or directionally until the target formation is reached and then kicking off horizontally to access the resource. The horizontal portion of a well can extend thousands of feet in a given direction. Because much more of the well is embedded in the target formation where the oil and gas exists, horizontal drilling allows for higher potential production from a given well. Multiple horizontal wells can also be drilled from the same well pad, allowing considerable resources to be accessed from a single site.
Drilling can take from days to months depending on the characteristics of the formation, the depth of the wells, and the number of wells to be drilled on a given well pad. Once the well operator verifies that a commercially viable quantity of gas or oil exists at the well site, the well will be ‘completed’.
Well completion involves strengthening the well with casings, testing pressure and temperature, creating flow of the resource into the well, and regulating the flow of the resource. Once all the casing is in place, tubing to carry the oil and/or gas in inserted down the length of the well. Then the production casing is sealed off with a plug and any surrounding cement or other barrier between the formation and the well is perforated. Half-inch to 1-inch holes are made by either small ‘bullets’ or via electrically ignited charges down the hole to allow the oil and/or gas to flow into the well from the adjacent rock. Rare ‘open hole’ completions, on the other hand, can be used in structurally sound geologic formations in which the resource is extracted directly into the bottom of the well.
Pressure and the rate of oil and gas production coming out of the well are regulated at a surface-level wellhead. While natural gas-only wells often do not require any lifting or treatment for the resource to enter and rise up through the well, some ‘tight’ natural gas wells and many mixed oil and gas wells do require some sort of lifting or treatment. Older wells for which the resource has been extracted to such an extent that pressure has decreased are also candidates for lifting or treatment. Lifting is used only when oil is the primary resource being extracted from a well and most commonly includes use of a pump jack. Treatments will vary according to a number of factors, but commonly include the injection of hydrochloric acid, water, gases (including natural gas associated with an oil well as well as CO2), or other materials down hole. Hydraulic fracturing – the injection of water, proppant (usually sand), and various chemicals down hole to pressurize the well, fissure and prop open the surrounding producing formation, and allow for the efficient extraction of oil and gas—has become an extremely commonplace treatment in Colorado and elsewhere where shale resources exist. Natural gas can also be produced as coal bed methane through a different set of extraction methods.
Hydraulic fracturing, or “fracking”, is the injection of water, proppant (usually sand), and various chemicals down hole to pressurize a well, make small (0.2”) fissures, and prop open the surrounding rock formation for the efficient extraction of oil and/or gas. Typical fracking solutions are made up of 90.5% water, 9% proppant (usually sand), and 0.5% chemical additives. For a well requiring 3 million gallons of water, over 16,500 gallons of chemical additives will be used.
Application of fracturing techniques to stimulate oil and gas production began to grow rapidly in the 1950s, although experimentation dates back to the 19th century. Starting in the mid-1970s, a partnership of private operators, the U.S. Department of Energy, and the Gas Research Institute (GRI) endeavored to develop technologies for the commercial production of natural gas from the relatively shallow Huron shale in the eastern United States. This led to advancements in downhole drilling motors and other equipment that made fracking and horizontal drilling more economically feasible. When pilot wells drilled with these technologies in Texas’s Barnett shale proved immensely productive by the early 2000s, the application spread to other shale formations across the country.
The surface landowner can influence the type and extent of reclamation activities. Requirements can vary depending on whether the disturbed area is private or federal land. In Colorado, reclamation activities which occur on private and state lands are regulated through the Colorado Oil and Gas Conservation Commission. Reclamation activities occurring on federal lands are regulated through the Bureau of Land Management and U.S. Forest Service.
Interim reclamation will occur during the productive life of a well. The objectives of interim reclamation are to reestablish vegetation, control weeds, re-contour surfaces, and restore the ecological functions of the disturbed area. Reinstating the disturbed site to its original state is the overall goal of final reclamation. This includes restoration of the surface land, natural resources such as crop production or wildlife habitat, and visual ascetics.