Abstract

Field data collected about Laramide paleostress trajectories from outcrop in the Big Bend region of Texas provide an opportunity for modeling both regional and local (σ stress fields, with the accompanying variations in stress trajectories caused by the superposition of local stress conditions upon the regional far-field stress conditions. Natural strain gauges in the form of mode I fractures and tectonic stylolites, whose teeth trend in the direction of the principal compressive stress, define the map representation of the (σ stress field. The paleostress field curvature as defined by these strain gauges was interpreted as a variation in the far-field stress trajectory initiated by local fracture development altering the shape of the stress field near these fractures. The paleostress field curvature was modeled using linear elastic theory and the principle of superposition. Three individual load conditions of varying orientation and magnitude were combined by superposition to model a single continuous paleostress field curvature. These stress fields are represented by: 1) the previously existing far-field stress; 2) the stress field due to local normal loading across the fracture; and 3) the stress field due to local tangential loading along the fracture. The mathematical models provide a powerful quantitative tool for subsurface fracture investigation within the oil and gas industry.