Constraining faults and stratigraphic zones in shale and tight oil basins via 3D geocellular models

Abstract

The validity of regional and basin-wide geomodels for unconventional and tight-oil plays depends on the accuracy and precision of the available structural and stratigraphic frameworks. Integrated reservoir models, combining seismic, log, core, and production data, are critical tools necessary for capturing the complexity of basin fill history and for understanding the 3D facies architecture. For researchers, a lack of publicly available 3D seismic surveys, even in basins with a high density of wells, is an impediment to creating accurate models of faults and stratigraphic zones. Three approaches were used to overcome this deficit: 1) well log correlation of detailed stratigraphic zones using densely spaced vertical wells; 2) calculation of trend surfaces from thousands of geosteered 3D horizontal well position logs; and 3) residual analysis of regional and local horizontal well trend surfaces to identify faults. Independent data were used in this work to confirm the validity of these new surfaces and faults, including 3D seismic interpretations (where available), well log-based fault correlations, and analysis of seismicity. The resulting horizons were used to increase the accuracy and precision of the structure and stratigraphy input for the 3D geocellular models. Examples of the approaches to refining geomodels are illustrated for the main North American unconventional reservoir and tight oil plays, including the Bakken, Barnett, Eagle Ford, Fayetteville, Haynesville, Marcellus, and the Midland and Delaware Basins. The horizontal well trend analysis techniques and workflows in this study will aid researchers attempting to build large, regional geocellular models for unconventional plays in improving the accuracy and precision of their 3D geocellular models through the improved constraint of faults and stratigraphic zones.