The Importance of Deformation Models for Calculating Reserves and Locating Wells in Overthrust Belts: Examples from the Mississippian Gas Fields of the NE British Columbia Foothills, Canada: ABSTRACT

Abstract

Understanding the deformation model appropriate for an oil or gas field in an overthrust belt has major consequences for the exploration and exploitation of these structures. Predicted reserves and well locations will be influenced by the model chosen. With Mississippian gas wells costing $1.2 to $1.5 mm each, a re-drill or even a whipstock to hit the target will negatively impact the bottom line. This is especially true if the reserves are 3Bcf as opposed to the 20Bcf originally predicted. For the purpose of this talk we will define two end-member deformation models: fault bend folds and detachment folds. The fundamental difference between the two models is that the fault bend fold has nearly equal amounts of displacement on both sides of the structure, whereas the detachment fold has the displacement absorbed by the fold. In the examples from British Columbia the reservoir formation is not directly imaged by seismic data. The top of it has to be [open quotes]ghosted in[close quotes] from the Permo/Penn event above it. If this is done using a constant thickness for the Permo/Penn to Mississippian interval this would be a more suitable technique for a fault bend fold model. As this area has amore » significant amount of detachment folding this technique is not appropriate. These differences in the deformation models will significantly impact both well location and reserve calculations.« less