Interpretational variability of structural traps: implications for exploration risk and volume uncertainty

Abstract

Abstract Defining the size and shape of hydrocarbon traps is a critical component in estimating the economic value of potential and existing oil and gas fields and is, therefore, a key business risk. Structural traps, defined by fault and fold geometries, form the most common type of hydrocarbon trap, the size estimates of which are based on interpretation of subsurface data, most notably seismic imagery. Interpretation of seismic image data is uncertain, as the subsurface images have limited resolution and quality; in 2D datasets the imagery is spatially limited and the interpretation requires interpolation between images. Here we present data from top reservoir maps created by eight interpretation teams, each of which interpreted a grid of 2D seismic sections at a regular spacing of 1 km, over a 220 km 2 area. The resultant maps are compared for interpretation variability. Fault statistics have been generated for each map and compared with analogue datasets to aid in the identification of anomalous interpretations, and to create a likelihood rank for each map. The structural traps identified by each team are compared, and the two largest traps are assessed for their potential trapped hydrocarbon volume. An initial volume and a corrected volume, accounting for potential fault seal breach by reservoir–reservoir juxtaposition across the trap-defining faults, are calculated. The integrated analysis of the multiple interpretations: (a) captures the interpretational uncertainty, (b) determines the likeliness (or risk) of each interpretation being valid, when compared with analogue datasets and (c) assesses the impact of each interpretation on the economic viability of potential prospects (defined by structural traps).