Modelling of sandbody connectivity in the Schooner Field

The Schooner field will be one of the first stand-alone developments of a gas accumulation in the Carboniferous Barren Red Measures Group of the UK Sector of the Southern North Sea. It illustrates the potential of Barren Red Measures Group as a future play in this area. The Schooner Field, located some 150 km (94 miles) east of the South Yorkshire coastline, is a NW-SE-oriented faulted dip closure. The reservoir consists predominantly of fluvial channel sandstones of the Barren Red Measures Group, with small amounts of gas located in the underlying Coal Measures Group. The sandstone channels are embedded in flood plain mudstones, which comprise 65–70% of the stratigraphic section. Because of the relatively low proportion of sandstone to mudstone, sandbody connectivity has been identified as the critical factor affecting recovery of gas. In order to asses the impact of sandbody connectivity on recovery efficiency, reservoir modelling work was performed based on eight different geological models and three well design options. The factors that were varied in order to build the geological models included (1) presence of minor faults, (2) the width of the channels, and (3) channel orientation. Well design options considered included (1) wells with deviations between 10 and 63°, (2) subhorizontal wells drilled along the strike of the structure, and 3) sub horizontal wells drilled along the dip of the structure. The results of the modelling work showed that sandbody orientation had the largest influence on connectivity, with connectivity being the highest when the channels were oriented along the strike of the structure. The width of the channels and the presence of minor faults had some impact on connectivity, while varying well design made little or no difference. Close inspection of the models did, however, show that the major faults compartmentalize the reservoir, resulting in large quantities of gas being by-passed if wells are not properly positioned. Consequently, more work is needed to evaluate the optimal location of the development wells.