Subsurface Structural Interpretation

Abstract Accurate three-dimensional (3-D) models of the deformed subsurface are foundational to successful oil and gas exploration and development, and modeling 3-D structural complexity in the subsurface requires specific skills and software. The gold standard in modern structural interpretation is the structural framework: an air-tight network of intersecting fault and horizon surfaces that completely describes the 3-D structural geometry of a given area, field, or prospect. The complete geometry of faulted reservoirs, petroleum traps, basin margins, and other deformed regions are more likely to be accurately captured in a structural framework because their construction workflow promotes sculpting mental models into physical products. Within exploration and production geologic settings, structural frameworks can be built only using volumetric interpretation software and workflows that allow for complete geometrical descriptions using incomplete sets of seismic, well, and other geologic data. The structural framework represents the highest possible interpretation achievement and relies on complementary skills in structural geology, spatial thinking, and digital tools. Although challenging to learn, and sometimes time-consuming to complete, there is a strong business case for dedicating resources to construct hi-fidelity frameworks. Technical and economic decisions rely on interpretation accuracy and confidence. Furthermore, nearly all advanced structural analyses, including fault-seal analysis, stress prediction, and fracture modeling require robust 3-D models at their foundation. Geologic maps or models that are not built within a 3-D environment commonly contain errors that misrepresent the degree or complexity of geologic deformation, or even the size and nature of an oil or gas prospect. The traditional structure map, and even the 2.5-D workstation workflow for mapping and understanding fault systems, for instance, is outdated and introduces uncertainty to a given interpretation because geometric validity of fault intersections, terminations, and others cannot be visually or graphically determined. In contrast, a 3-D framework provides a representation of structural geometries that is much easier to assess and edit. The examples provided here demonstrate the power and utility of structural frameworks in oil and gas exploration and development, and are testament to their role as the new standard in structural interpretation as the industry explores in increasingly challenging geological settings in the 21st century.