ABSTRACT:

Successful placement of a horizontal well requires accurate landing of the well in the desired position and orientation in the reservoir. Operators face operational and economic challenges in achieving accurate landing due to limited seismic resolution, in addition to uncertainty in the reservoir position, orientation, and overall geological structure. These challenges are further amplified by the increasing geological complexity of the reservoirs being drilled today. The current industry practice for landing a well is to use real-time logging while drilling (LWD) measurements to detect expected signatures or markers before entrance into the reservoir (Clark 1988). By comparing offset well data and geological models, these relatively shallow depths of investigation LWD measurements are used to indirectly infer the location and orientation of the "sweet spot". As the target interval is not imaged directly, the well trajectory adjustments may not result in optimal placement of the well for the horizontal section. To check the validity of geological models for landing calculations, operators frequently drill pilot wells to delineate the local reservoir features and at the same time collect petrophysical data to facilitate reservoir characterization. A sidetrack is then drilled to land the well based on the assumption that the reservoir structure does not show significant lateral changes from the pilot well. Drilling a pilot well is both costly and risky especially when drilling in deeper waters where operating costs are high (Ayodele 2004). Following a earlier prototype design of a non-directional resistivity tool (Seydoux, 2004), a new deep directional electromagnetic (EM) LWD service with a radial depth of investigation in the order of 30 m (100 ft) has been introduced in Brazil. The 8.25 in. diameter tool (for 12 ¼ to 14 in. hole sizes) addresses landing applications and structure delineation.

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