A major challenge facing the oil industry is optimizing horizontal wellbore placement in a reservoir. Uncertainty in the predrill geological model and seismic interpretation may lead to the well being placed in non-reservoir, or steering the well out of the prospective formation. This can lead to lower well performance or the requirement to sidetrack the wellbore, both of which directly impact the profitability of the operation.

The Nipisi D Pool produces oil from the Middle Devonian Slave Point Formation, a regionally extensive carbonate bank characterized by low permeability limestone reservoir. The advent of horizontal drilling (HZ) and completion technologies has elevated this reservoir to a top tier tight oil resource play. Although HZ drilling provides a cost effective means to reservoir development, maximizing reservoir penetration while avoiding the unstable shale above the Slave Point are imperative.

Structural definition of the reservoir is provided by 3D seismic coverage. This provides a good predrill estimate of wellbore trajectory, however is limited in its vertical accuracy, as well as definition of small-throw faults that do not appear to be imaged on the seismic data. These two limitations introduce a real risk of drilling out of the productive zone.

Using the contrast in resistivity between the productive carbonate reservoir and the low resistivity Waterways shale which overlies it, deploying Measurement-While Drilling (MWD) deep azimuthal resistivity tools provided the operator with higher resolution measurements to detect the top of reservoir and keeping the wellbore within the desired reservoir. This paper focuses on the integration of geological/3D seismic mapping and MWD azimuthal resistivity for optimal HZ well placement in a tight limestone reservoir, as well as the limitations of each technology when used in isolation. It illustrates how utilizing this approach the operator was able to achieve 100% reservoir exposure.

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