William A. Olsson1, John C. Lorenz2, Scott P. Cooper1
(1) Sandia National Laboratories, Albuquerque, NM
(2) Sandia National Laboratories, Alberquerque, NM
ABSTRACT: Multiply-Oriented Conjugate Deformation Bands: Effects on Reservoirs and Constraints on Stress History
Three pairs of conjugate deformation bands are present in Jurassic sandstones in the southeastern corner of the San Juan basin, northwestern New Mexico. In order of development, these pairs are oriented to form each of the three principal conjugate attitudes: upright, plan-view, and recumbent X's. One possible explanation for the sequential formation of such features is that the maximum compressive stress orientation changed with time due to changes in the local structural history. However, the axes of the different "X" geometries are parallel, suggesting that the sets are genetically related. We propose that a simpler stress history, with the horizontal stresses striking northeast and southeast and varying in magnitude but not in orientation, would also plausibly explain this sequential development. In this model, the upright X's formed under initial conditions where the overburden was the maximum and the northeast-striking horizontal stress the intermediate stress. Plan-view X's formed next as the northeast-striking stress increased (due to northeastward Laramide translation of the Colorado Plateau and interaction with the local basement-cored uplift) to become the maximum stress, leaving the overburden stress as the intermediate stress although unchanged in magnitude. As the northeast-directed horizontal stress continued to increase it created conditions where both horizontal stresses exceeded the overburden, resulting in incipient thrust faulting of the recumbent X's. Mechanically, it can be shown that stress levels dropped temporarily once they reached failure at each stage, interrupting deformation so that no overlap occurred. The three sets of intersecting conjugate deformation bands resulted in extremely compartmentalized potential reservoirs.
AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado