The Foothills of the Canadian Rocky Mountains are a classic example of a thin-skinned fold-thrust belt. A regionally significant detachment in the shales of the Jurassic Fernie Formation separates the intensely folded and imbricated clastics of the Jurassic and Cretaceous from the thrust structures in the prospective dolomite reservoirs of the Triassic and upper Paleozoic.

The Monkman area lies within the foothills of northeastern British Columbia and contains a number of fields that produce sour gas from the platform carbonates of the Upper Triassic Pardonet and Baldonnel Formations. The current phase of drilling commenced in 1987 and has been remarkably successful, with numerous gas discoveries made at a 75% success rate. The area is topographically difficult and structurally complex, with a number of detachments that compartmentalize the deformation within distinct tectonostratigraphic units. The acquisition, processing, and interpretation of seismic data in this area is technically difficult and requires careful analysis to yield good results. The integration of the seismic, well, and surface-geology data is essential for the accurate definition of subsurface targets.

The traps are primarily fault-propagation and detachment folds that detach in the shale-dominated Lower Triassic. The structural style has been interpreted from stratigraphic data, VSP data, and detailed dip data provided by imaging tools. Fracturing is pervasive in the hinges and forelimbs of the folds, and it enhances the tight reservoir to yield typical flow rates of 40 million cubic feet of gas per day (mmcfg/d). The key to success in the play is to target these zones of the folds. However, this is not always successful initially, because the original wellbores often miss the structures. The case studies we present show how revised structural models that incorporate data from the original wellbores increase the chance of success in sidetracking a well into the preferred target area.