The Missippian [sic] Leadville Limestone Exploration Play, Utah and Colorado

Title: The Missippian [sic] Leadville Limestone Exploration Play, Utah and Colorado: Exploration Techniques and Studies for Independents
Author: Thomas C. Chidsey, Jr.
Publication: The Outcrop, October 2004, p. 1, 6

On September 30, 2003, the U.S. Department of Energy (DOE) awarded funding to the Utah Geological Survey (UGS) for a project titled “The Mississippian Leadville Limestone Exploration Play, Utah and Colorado – Exploration Techniques and Studies for Independents” as part of its Advanced and Key Oilfield Technologies for Independents (Area 2 –  Exploration) program. The purpose of this program is to “expand the knowledge base through which industry can bring additional oil reserves and new technology options into the marketplace in a cost effective and environmentally acceptable manner.” This effort is designed to push the limits of standard exploration technologies and improve them. The total cost of this new, 3.5-year UGS project, one of three selected out of 28 proposals, will be about $536,000 with 50 percent cost share from DOE.

The Mississippian Leadville Limestone has produced over 53 million barrels of oil from six fields in the northern Paradox Basin region of Utah and Colorado. All of these fields (except Lisbon, which was operated by Tom Brown Inc., now EnCana) are currently operated by small, independent producers, and only independent companies explore for Leadville oil targets in the region, 85 percent of which is under the stewardship of the federal government. This environmentally-sensitive, 7,500-square-mile area is relatively unexplored with only about 100 exploratory wells that penetrated the Leadville (less than one well per township), and thus the potential for new discoveries remains great.

Oil is produced from the Leadville Limestone in structural traps with closure on both anticlines and faults. The Leadville is a shallow, open marine, carbonate shelf deposit. Crinoid banks (primary reservoir facies) or mounds accumulated in shallow-water environments on upthrown fault blocks or other paleo-topographic highs.

Lead photo
Paradox Basin of Utah and Colorado showing the location of oil fields productive from the Mississippian Leadville Limestone; the thickness of the Leadville is also shown (contour interval = 100 feet). Modified from Parker and Roberts, 1963.

The overall objectives of this proposed study are to: (1) develop and demonstrate techniques and exploration methods never tried (and documented) on the Leadville Limestone, (2) provide the facies, hydro-dynamic pressure regime, and oil show quality maps that will be used to target areas for exploration, (3) increase deliverability from new and old Leadville fields through detailed reservoir characterization, (4) reduce exploration costs and risk especially in environmentally sensitive areas, and (5) add new oil discoveries and reserves.

The project will be conducted over two phases, each with specific objectives and separated by a continue-stop decision point based on results to date. The objectives of Phase 1 will be to conduct a case study of the Leadville reservoir at Lisbon Field (the largest Leadville producer), San Juan County, Utah, in order to understand the reservoir characteristics and facies that can be applied regionally. The objectives of Phase 2 will be to first conduct a low-cost field demonstration of new exploration technologies to identify (1) potential Leadville oil migration directions (evaluating the middle Paleozoic hydrodynamic pressure regime), and (2) surface geochemical anomalies (using microbial, soil, gas, iodine, and trace elements), especially in environmentally sensitive areas. The second objective will be to determine regional facies (evaluating cores, geophysical well logs, outcrop and modern analogs), identify potential oil-prone areas based on shows (using low-cost epi-fluorescence techniques), and target areas for Leadville exploration.

These objectives are designed to assist the independent producers and explorers who have limited financial and personnel resources. All project maps, studies, and results will be publicly available in digital or hardcopy format and presented to the petroleum industry through a proven technology transfer plan. The technology transfer plan includes a Technical Advisory Board composed of industry representatives operating in Utah and a Stake Holders Board composed of representatives of state and federal government agencies, and groups with a financial interest within the study area. Currently there are 16 members of the Technical Advisory Board which met for the first time on August 13, hosted by Bill Barrett Corporation in Denver. Project goals, plans and results were presented to the Board.

For more information on this project, contact Roger Bon by phone at 801-537-3363 or by e-mail at or check out the project website at

David Eby and Thomas Chidsey will be presenting a talk entitled “A Tale of Two Dolomites (Syngenetic vs. Hydrothermal) Mississippian Leadville Reservoirs at Lisbon Field, Paradox Basin, Utah” at the RMAG Hydrothermal Dolomite Symposium & Core Workshop, November

15, 2004.