Burial and thermal history of the Paradox Basin, Utah and Colorado, and petroleum potential of the Middle Pennsylvanian Paradox Formation

The Ismay-Desert Creek interval and Cane Creek cycle of the Alkali Gulch interval of the Middle Pennsylvanian Paradox Formation in the Paradox Basin of Utah and Colorado contain excellent organic-rich source rocks having total organic carbon contents ranging from 0.5 to 11.0 percent. The source rocks in both intervals contain types I, II, and III organic matter and are potential source rocks for both oil and gas. Organic matter in the Ismay-Desert Creek interval and Cane Creek cycle of the Alkali Gulch interval (hereinafter referred to in this report as the "Cane Creek cycle") probably is more terrestrial in origin in the eastern part of the basin and is interpreted to have contributed to some of the gas produced there.

Thermal maturity increases from southwest to northeast for both the Ismay-Desert Creek interval and Cane Creek cycle, following structural and burial trends throughout the basin. In the northernmost part of the basin, the combination of a relatively thick Tertiary sedimentary sequence and high basinal heat flow has produced very high thermal maturities. Although general thermal maturity trends are similar for both the Ismay-Desert Creek interval and Cane Creek cycle, actual maturity levels are higher for the Cane Creek due to the additional thickness (as much as several thousand feet) of Middle Pennsylvanian section.

Throughout most of the basin, the Ismay-Desert Creek interval is mature and in the petroleum-generation window (0.10 to 0.50 production index (PI)), and both oil and gas are produced; in the south-central to southwestern part of the basin, however, the interval is marginally mature (<0.10 PI) for petroleum generation, and mainly oil is produced. In contrast, the more mature Cane Creek cycle contains no marginally immature areas—it is mature (>0.10 PI) in the central part of the basin and is overmature (past the petroleum-generation window (>0.50 PI)) throughout most of the eastern part of the basin. The Cane Creek cycle generally produces oil and associated gas throughout the western and central parts of the basin and thermogenic gas in the eastern part of the basin.

Burial and thermal-history models were constructed for six different areas of the Paradox Basin. In the Monument upwarp area, the least mature part of the basin, the Ismay-Desert Creek interval and Cane Creek cycle have thermal maturities of 0.10 and 0.20 PI and were buried to 13,400 ft and 14,300 ft, respectively. A constant heat flow through time of 40 mWm^-2 (milliwatts per square meter) is postulated for this area. Significant petroleum generation began at 45 Ma for the Ismay-Desert Creek interval and at 69 Ma for the Cane Creek cycle.

In the area around the confluence of the Green and Colorado Rivers, the Ismay-Desert Creek interval and Cane Creek cycle have thermal maturities of 0.20 and 0.25 PI and were buried to 13,000 ft and 14,200 ft, respectively. A constant heat flow through time of 42 mWm^-2 is postulated for this area. Significant petroleum generation began at 60 Ma for the Ismay-Desert Creek interval and at 75 Ma for the Cane Creek cycle.

In the area around the town of Green River, Utah, the Ismay-Desert Creek interval and Cane Creek cycle have thermal maturities of 0.60 and greater and were buried to 14,000 ft and 15,400 ft, respectively. A constant heat flow through time of 53 mWm^-2 is proposed for this area. Significant petroleum generation began at 82 Ma for the Ismay-Desert Creek interval and at 85 Ma for the Cane Creek cycle.

Around Moab, Utah, in the deeper, eastern part of the basin, the Ismay-Desert Creek interval and Cane Creek cycle have thermal maturities of 0.30 and around 0.35 PI and were buried to 18,250 ft and 22,000 ft, respectively. A constant heat flow through time of 40 mWm^-2 is postulated for this area. Significant petroleum generation began at 79 Ma for the Ismay-Desert Creek interval and at 90 Ma for the Cane Creek cycle.

At Lisbon Valley, also in the structurally deeper part of the basin, the Ismayy–Desert Creek interval and Cane Creek cycle have thermal maturities of 0.30 and greater than 0.60 PI and were buried to 15,750 ft and 21,500 ft, respectively. A constant heat flow through time of 44 mWm^–2 is postulated for this area. Significant petroleum generation began at 79 Ma for the Ismay–Desert Creek interval and at 100 Ma for the Cane Creek cycle.

The area around Hermosa, Colo., in the southeastern part of the basin, has experienced a shallower burial history than the other areas in the basin, yet it has one of the highest thermal maturities. Here, the Ismay–Desert Creek interval and Cane Creek cycle have vitrinite reflectance values of 1.58 and 1.63 percent and were  buried to 13,700 ft and 15,500 ft, respectively. Due to Tertiary igneous activity in this part of the basin, a variable heat flow is proposed: from 600 to 30 Ma, 45 mWm^–2; from 30 to 25 Ma, 63 mWm^–2; and from 25 Ma to present, 50 mWm^–2. Significant petroleum generation began at 72 Ma for the Ismay–Desert Creek interval and at 76 Ma for the Cane Creek cycle.