A Methodological Approach to Clastic Injectites

Abstract

Hardly detected with logs and recognized with difficulty on cores, clastic injectites (sills and dikes) can be troublemakers in oil-field development. Moreover, they provide a precious record of early fracturation. To predict their geometry, extension, and relationship to their feeders, field analysis of selected analog outcrops is conducted to propose some simple rules. In southeast France, the Aptian–Albian formation provides exceptional outcrops (Bevons, Rosans, and Nyons) where it is possible to characterize large sets of injectites: dikes and sills are associated in the same metric-to-kilometric network. The injection occurred per ascensum (more frequently) or per descensum, during or after the sand deposition. Specific geometric-based field methods have been developed to analyze the geometry based on the best conditions. A three-dimensional (3-D) model of the Rosans area injectite network has been built through gOcad™ tool using outcrop analysis and an original, very high-resolution two-dimensional seismic acquisition (0.6 km2; 0.23 mi2). This field analysis, the seismic survey, and the 3-D modeling provide some keys to consider possible occurrences of injectites and associated facies related to a turbiditic channel fill. We dedicate this article to the memory of our colleagues and friends G. P. Allen and D. Claude.