New Techniques for New Discoveries
Results from the Lisbon Field Area, Paradox Basin, Utah

Authors: David M. Seneshen, Direct Geochemical, Golden, CO; Thomas C. Chidsey, Jr., Craig D. Morgan, and Michael D. Vanden Berg, Utah Geological Survey (UGS), Salt Lake City, UT.

Venue: American Association of Petroleum Geologists annual convention, Long Beach, CA, April 1–4, 2007 (http://www.aapg.org/ [external site]).

Abstract: Innovative surface geochemical techniques were tested over Mississippian Leadville Limestone reservoirs of Lisbon oil and natural gas field and a new Leadville gas discovery in the Paradox Basin of southeast Utah. The traps for both fields are elongate northwest-trending anticlines bounded on the northeast flanks by large normal faults. The objective of this study is to test low-cost geochemical methods for detecting hydrocarbon microseepage over productive hydrothermal dolomite reservoirs, especially in areas with extensive outcrops. About 400 soil samples were collected along grid lines over 15 square miles and analyzed for C₁-C₁₂ hydrocarbons, heavy aromatic hydrocarbons, 53 major and trace elements, and 7 anion species. In addition, vegetation tissue and soils from joints in outcrops of the Jurassic Navajo and Wingate Sandstones were sampled to compare with the soil results. Free gas samples were collected from 6-ft depth over the new discovery and known non-productive areas off the structures. Results to date are very encouraging. Productive and non-productive areas can be distinguished based on absolute concentrations of hydrogen, propane, nButane, nPentane, and carbon dioxide in free gas samples. Microseepage in soils is also different in terms of synchronous scanned fluorescence spectral patterns. The discriminant function separating microseepage over productive and non-productive areas correctly predicts the location of the new production southwest of Lisbon. Sulphate and chloride increase along suspected faults near production, which probably reflects the ascent of brines to the surface from the underlying Pennsylvanian Paradox Formation. The results of other analyses (i.e., C₁-C₁₂ and major/trace elements) will also be presented.

Related NETL Project: The goals of the related NETL project entitled “The Mississippi Leadville Limestone Exploration Play of Utah and Colorado—Exploration Techniques and Studies for Independents” (DE-FC26-03NT15424) are to 1) develop and demonstrate techniques and exploration methods never tried on the Leadville Limestone; 2) 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.

NETL Project Contacts:
NETL – Virginia Weyland (virginia.weyland@netl.doe.gov or 918-699-2041)
UGS – Thomas Chidsey, Jr. (tomchidsey@utah.gov or 801-537-3364)