Horizontal drilling and hydraulic fracturing are commonplace in the shale plays across the United States with successful wells efficiently yielding large volumes of shale gas and oil at minimum time and cost. Typical well profiles involve building a curve and then drilling long horizontal sections to TD, with the horizontal section taking up to 7000ft to complete. One of the most cost effective means to drill such wells is with Positive Displacement Motor (PDM) Bottom Hole Assemblies (BHAs) consisting of PDMs with bend angles for directional control.

When addressing drilling efficiency; a major contributor is BHA selection and the ability to select the most efficient combination of bit, PDM and stabilizer arrangement for each specific application. It is this selection process that forms the basis of this paper which details how a new suite of analysis tools were developed to analyse the dynamic behavior of a PDC bit on PDMs with variable bend angles and stabilizer configurations. Drilling on a bent motor in rotational mode has long proven challenging for both PDM and bit and the complex dynamic behavior has rarely been fully understood let alone analyzed.

At the heart of the new suite of tools is the capability to analyse the complex trajectory of the cutting structure of the bit to simulate the Bottom Hole Pattern (BHP) created in the rock. Having understood the transient behavior of the bit, an analysis tool was then developed to analyse the drilling behavior of the bit and BHA which resulted in a new approach to PDC bit design for bent motor BHA applications with the design intent of providing smoother drilling, increased durability and higher rates of penetration.

The first run of the new design of bit resulted in improved drilling performance, allowing the customer to drill the complete section to TD using a 2.38° bent motor BHA for the first time in the Marcellus. The negated need for multiple trips ultimately saved the customer up to 25% in completion time resulting in a cost saving of approximately $128k.

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