ABSTRACT: Regional Tectonic Analysis as a Guide in Orientation of Horizontal Drill Holes to Explore Fracture Reservoirs in Hydrocarbon Source Rocks Unaffected by Local Folding and Faulting

WOODWARD, LEE A., University of New Mexico, Albuquerque, NM

To predict the orientation of open fractures in the subsurface of underexplored areas, it is necessary to understand the stress fields that affected the host rock for the potential fracture reservoir. The first step is to ascertain structural development using a regional tectonic synthesis and analysis. This involves determining the structure and kinematics (movements), which allows one to interpret the stress field responsible for the movements and structures. Tools useful in obtaining the structural geometry include structure contour, isopach, gravity anomaly, and magnetic anomaly maps. Lithofacies maps help detect paleotectonic features not shown by structure contour or isopach maps.

Linear features that may represent fractures at the surface should be used cautiously in extrapolating trends into the subsurface because some trends of subsurface fractures may differ from surface trends.

Open, extensional fractures form in planes parallel to the direction of maximum horizontal stress and are approximately perpendicular to the direction of least compressive stress. Fluid overpressuring generally occurs in rocks with low indigenous permeability during hydrocarbon generation and may lead to a set of parallel fractures. Extensional fractures can form at considerable depth with high lithostatic pressure if there is fluid overpressuring and differential regional tectonic stress. Thus, it is important to know as closely as possible the time of hydrocarbon generation and, therefore, the likely time of fracturing. If the stress field at the time of fracturing can be deduced, it is possible to infer the orientation of open fractures.

AAPG Search and Discovery Article #91017©1992 AAPG Rocky Mountain Section Meeting, Casper, Wyoming, September 13-16, 1992 (2009)