271 wells producing exclusively from the Nikanassin and equivalent Formations in a very large area of over 15,000 square kilometers in the Western Canadian Sedimentary Basin (WCSB), Alberta and British Columbia, Canada, have been evaluated with a view to determine the distribution of cumulative gas production and the possibilities of intensive infill drilling.
The Upper Jurassic to Lower Cretaceous Nikanassin formation is generally characterized as a tight gas formation with low values of permeability (typically a fraction of millidarcy) and low porosities (usually less than 6%). It is likely that natural microfractures and slot pores dominate the productivity of the formation. The study area was divided into 6 smaller narrow areas (A to F) approximately parallel to the NW-SE trending thrust belt of the Canadian Rocky Mountains. Area ‘A’ is located to the west of the deformation edge, area ‘B’ is on the deformation edge, and areas ‘C’ to ‘F’ are located to the east. Area ‘C’ is the deepest and closest to the thrust belt, whereas area ‘F’ is the shallowest and furthest from the thrust belt.
Cumulative production characteristics within each area were evaluated with a variability distribution model (VDM) developed recently for naturally fractured reservoirs. The evaluation of each one of the 6 areas (271 wells) resulted in coefficients of determination, r2, greater than 0.99 in all cases. The results indicate that the gas cumulative production distribution per well is more homogeneous along the deformation edge (area B), where 80% of the wells contribute approximately 50% of the cumulative production. The highest heterogeneity was found in area F (the shallowest) with 80% of the wells contributing only 25% of the cumulative gas production. Areas A, B, D and E have more or less the same distribution with 80% of the wells contributing between 35% and 45% of the cumulative gas production. Preliminary, there is an association between the cumulative production distribution and lateral variations of borehole breakouts in the Nikanassin formation on a transect perpendicular to the deformation belt of the WCSB.
Analysis of the distributions leads to the conclusions that the Nikanassin is a very heterogeneous formation and that there is significant potential for massive drilling to efficiently drain the formation. The possibilities of horizontal wells and multi-stage hydraulic fracturing jobs are being investigated at this time.