Cooper, Scott P.¹, Paul M. Basinski², Rich Larson³, James M. Herrin¹, Russell G. Keefe¹
(1) Sandia National Laboratories, Albuquerque, NM
(2) El Paso Production Company, Houston, TX
(3) Vermejo Park Ranch, Raton, NM

ABSTRACT: Natural Fracture Patterns within the Raton Basin of Colorado and New Mexico

Suites of natural fracture data from wireline logs, core, and outcrop provide a unique view of the subsurface fracture system within the Raton basin of Colorado and New Mexico. The patterns and distributions of fractures are related to mechanical stratigraphy caused by different lithologies, diagenesis, and compaction. Thus the varied stratigraphic units exhibit unique fracture patterns. Both extension and conjugate shear fractures occur within fluvial sandstones of the Raton Formation whereas extension fractures dominate the laterally extensive Trinidad Sandstone. Extension fractures are most common within the Niobrara Limestone although conjugate shear fractures also occur locally. Shear fractures dominate the silicic Dakota Sandstone.
Regional fractures in Cretaceous and Tertiary strata in the basin are related to Laramide-age eastward thrusting of the Sangre de Cristo Mountains at the western margin of the basin. This relationship is indicated by extension fracture orientations that strike approximately east-west, normal to the thrust front, and proven by the related conjugate shear fractures where the bisector to the acute angle is also normal to the thrust front. These indicate that the maximum compressive stress was horizontal and oriented east-west at the time of fracturing. Such fractures and east-west face cleats in coals occur as far east as the margin of the basin, 75 miles from the thrust front. However, local structures within the basin, including anticlines and normal and thrust faults, created local fracture patterns markedly different from the surrounding east-west regional fracture pattern. Preliminary well interference data support a north-south oriented permeability trend in local areas.

AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.