Oil and Gas Potential of Wyoming: ABSTRACT

Abstract

Through 1978 Wyoming had produced 4.6 billion bbl of oil and had a year-end estimated 1.8 billion bbl in known fields (includes proved reserves, NGL, future extensions, revisions, new-pool discoveries, and enhanced recovery). Production and reserves are between 3 and 4% of United States totals. Approximately 55% of past oil production has been from Paleozoic rocks, primarily Permian-Pennsylvanian, and 35% from Cretaceous sandstones. Reserves in Cretaceous rocks probably are greater than those in Paleozoic rocks, but the importance of Jurassic reservoirs is increasing. Three-fourths of past discoveries have been in structural traps, but, with the exception of the thrust belt, future discoveries will be largely in stratigraphic traps. Through 1978 Wyoming had produced 7.6 Tcf of natural gas and had an estimated 9.8 Tcf in known fields (includes proved reserves, future extensions, revisions, and new-pool discoveries). Production and reserves are between 1 and 2% of the United States totals and are concentrated in Cretaceous sandstones--Cretaceous rocks in stratigraphic traps will dominate future production. Average annual oil production during the past 20 years has been 139 million bbl. With reasonable economic incentives, future discoveries should permit production at this level to continue to the year 2000. Average annual gas production during the past 20 years has been 300 Bcf. Development of known gas accumulations and future discoveries should permit an increase End_Page 829------------------------------ in annual production to approximately 900 Bcf by 1990 and this production level should continue to the year 2000. Estimated undiscovered oil resources range from 2 (95% probability) to 8 (5% probability) billion bbl with 4 billion bbl the most likely quantity. The most promising area for future discoveries (barring bandwagon psychology!) is the thrust belt with an estimated range of 600 million to 3 billion bbl and a most likely estimate of 1.5 billion bbl. Future discoveries in the thrust belt will be in structural traps in Mesozoic and Paleozoic formations. Close behind the thrust belt in estimated undiscovered oil resources is the Powder River basin with a range of 500 million to 3 billion bbl and a most likely estimate of 1 billion bbl. Future discoveries should be in Pennsylvanian and Cretaceous rocks, in stratigraphic traps, within the central, deeper part of the basin. Other parts of Wyoming have a wide variety of possible traps and potentially productive formations. There is a long-shot chance for giant oil or gas accumulations in Permian-Pennsylvanian stratigraphic traps in the Wind River and Green River basins, similar to the Cottonwood Creek field in the Bighorn basin. These will be deep! Estimated undiscovered gas resources range from 35 (95% probability) to 100 (5% probability) Tcf with 56 Tcf the most likely quantity. Future major gas discoveries will be in Tertiary, Cretaceous, and pre-Cretaceous rocks in the Green River and Wind River basins. These basins have an average range in potential from 11 to 47 Tcf and a most likely estimate of 21 Tcf in each basin. The Wyoming portion of the thrust belt has an estimated range in potential of 8 to 20 Tcf and a most likely estimate of 12 Tcf undiscovered, but these estimates are subject to considerable change as developments continue. A significant portion of the gas potential is in tight sandstones that have less than 1 md permeability. Greatly increased wellhead prices and improved fracturing technology would permit ultimate gas production to be larger than the most likely estimates. End_of_Article - Last_Page 830------------