Pinedale Anticline

By Ranie Lynds

SUBLETTE COUNTY –The Pinedale Anticline is vitally important for the nation’s energy needs. Looking out at the sagebrush landscape, when driving south of town, it is hard to believe that this geologic anticline includes one of the largest gas fields in the world.

Since drilling began in the late 1990s, this area has provided nearly 5 trillion cubic feet of natural gas to the nation…and up to 40 trillion cubic feet in the coming years. Wyoming is 5th in the production of natural gas in the United States. More than half of U.S. homes are powered by natural gas. The Pinedale Anticline in Wyoming helps power U.S. homes.

Pinedale field is the largest gas field in Wyoming and the sixth largest in the United States. This giant field is named after the Pinedale anticline, a northwest-southeast trending folded structure about 5 mi (8 km) wide and 35 mi (56 km) long.

The Pinedale anticline was first delineated by detailed geologic mapping in the 1920s. In 1939, the first well drilled to explore for oil on this structure was California Company’s Government #1, to a depth of 10,002 ft (3,049 m). There were no oil shows in this well, and although there were gas shows, there was not a market for natural gas and the well was eventually plugged and abandoned.

As the demand for natural gas grew over the ensuing decades, numerous exploration efforts attempted to unlock the hydrocarbons from the reservoir rocks.

Production in the Pinedale field is from the “Lance Pool” — nearly 6,000 feet (1,800 m) of fluvial and alluvial sedimentary rocks that are Upper Cretaceous through Tertiary in age (approximately 83 to 60 million years old), and include the upper Mesaverde Group, Lance Formation, and lower Wagon Wheel Formation.

The reservoirs on the Pinedale anticlines are “tight,” meaning they have very low porosity (average 7 percent) and permeability (micro-Darcy), and that producing the hydrocarbons requires fracturing the reservoirs to create flow pathways.

In 1969, drilling began on the Wagon Wheel #1 well that was completed in cooperation with the U.S. Atomic Energy Commission for the purpose of evaluating nuclear devices to fracture tight reservoirs and stimulate hydrocarbon production. However, the program was abandoned before these tests could be carried out.

The first significant production from the Pinedale field came in 1983 when natural gas was transported via truck from the Mesa Unit #1 and #2 wells.

Modern production began in 1998 with the Mesa 15-8 well, the first multi-stage fracture-stimulated well in the Pinedale field. Success from the Mesa 15-8 well paved the way for the production boom that occurred in the late 1990s and early 2000s.

To date, the Pinedale field has produced more than 4.9 trillion cubic feet of natural gas and 37 million barrels of oil (primarily as condensate). In 2014, natural gas extraction in the Pinedale field accounted for 1.6 percent of the nation’s natural gas production. Current estimates suggest approximately 39 trillion cubic feet of natural gas is expected to be recovered from the Pinedale field.

Exploration, technology, and environmental concerns have played major roles in the development of this giant natural gas field. Although active exploration no longer occurs on the anticline, infill drilling is common.

The Bureau of Land Management’s 2008 Supplemental Environmental Impact Statement Record of Decision (SEIS ROD) planned for 4,399 additional wells with an estimated 40 years of production. Operators currently follow a plan of concentrated development, where drilling is confined to a small part of the anticline in an effort to leave large parts of the area undisturbed for wildlife.

Technological improvements have also minimized surface disturbance. Up to 50 wells can now be drilled from a single well pad with a shared production facility, and drill time per well has been reduced from more than 60 days in the early 2000s to an average of 12 days in 2013.

Further, environmental concerns have been addressed through the process of adaptive management. This is one of the first oil and gas development areas in the country that provided a way to propose changes to the SEIS ROD based on scientific results studied in the field. Adaptive management has led to more stringent requirements on air pollution, resulting in completions without flaring and the elimination of non-essential operations on high ozone days.

Development of the Pinedale field is a good example of operators, private landowners, and state and federal agencies working together in an attempt to strike a balance between hydrocarbon exploration and production for current human needs while preserving cultural and environmental resources for the future.