If you want to understand Colorado oil, you need to understand one basin: the Denver-Julesburg Basin, or DJ Basin. This is where almost all of Colorado's oil comes from. The DJ Basin is a relatively quiet-looking place on the surface — flat farmland and small towns north of Denver. But underground, it holds billions of barrels of oil locked in tight rock formations.
What Is a Basin?
A basin is a large area where the earth's surface has sunk down compared to the surrounding land. Over millions of years, sediment — sand, mud, and the remains of living things — fills the basin. The weight compresses the lower layers into rock. If the right conditions existed, organic material in those rocks turned into oil and natural gas. The DJ Basin formed this way over hundreds of millions of years.
Where Does the DJ Basin Sit?
The DJ Basin covers the northeastern corner of Colorado, a thin strip of southeastern Wyoming, and small parts of Nebraska and Kansas. The basin is about 70,000 square miles total. The deepest part of the basin — where the oil is most concentrated — sits under Weld County, Colorado. Weld County alone produces more oil than most U.S. states, making it one of the most important counties in American energy production.
What Formations Produce Oil?
The DJ Basin has several oil-bearing formations, but two stand out:
- Niobrara Shale (and Chalk). The Niobrara is the main target. It formed about 85 million years ago when a warm inland sea covered the middle of North America. Tiny marine creatures died and settled on the seafloor. Over time, those remains became a waxy shale and chalky limestone rich in oil. The Niobrara has three main sub-layers called benches: the A Bench, B Bench, and C Bench. The B Bench is generally the richest in oil. Drillers run horizontal wells through each bench separately.
- Codell Sandstone. The Codell sits just below the Niobrara. It is a tight sandstone — meaning oil is trapped in tiny pore spaces and needs fracking to flow. Codell wells tend to produce more natural gas and natural gas liquids alongside oil. Many operators drill Codell wells on the same pad as Niobrara wells to squeeze more production from one location.
Below these formations, there are deeper conventional targets — older sandstones that produce smaller amounts of gas and oil. But the modern DJ Basin boom is almost entirely about the Niobrara and Codell.
How Deep Are These Formations?
In the core of the DJ Basin around Weld County, the Niobrara sits roughly between 6,000 and 8,500 feet underground. The Codell sits just below it — sometimes only a few hundred feet deeper. These are not unusually deep formations, which keeps drilling costs relatively manageable compared to deeper basins like the SCOOP in Oklahoma or the Bakken in North Dakota.
What Makes a Good DJ Basin Well?
The best DJ Basin wells are in the over-pressured core of the basin — areas where underground pressure is higher than normal. Higher pressure pushes oil out of the rock faster and gives wells stronger early production rates. The core of the over-pressured zone sits in eastern Weld County. Wells there can produce 1,000 barrels per day or more in their first month. Moving away from the core, pressure drops and well performance declines.
How Does Historical Data Help?
The DJ Basin has been drilled since the 1940s. There are tens of thousands of old conventional gas wells in the basin alongside the newer horizontal oil wells. Those old wells recorded formation depths and any oil or gas shows found during drilling. COGCC records going back decades are publicly available. ScoutTickets.io maps this historical data alongside modern production results so you can see the full picture of what any DJ Basin prospect might hold.