Maximizing well productivity and improving drilling efficiency remains a major challenge while drilling horizontal wells in US-land unconventional shale plays in the last few years. Reducing drilling times and eliminating trips for the curve bottomhole assembly (BHA) requires a motor that can be rotated at high RPM in the vertical section while still achieving buildup rate (BUR) in the curve. The challenges of horizontal well drilling in US land led to the recent introduction of a steerable optimized design motor (ODM) with a short bit-to-bend (BTB) distance. These ODMs achieved higher BUR in the curves than the conventional motors at lower adjustable kick-off (AKO) sub angle. Although the planned dogleg severities (DLS) stayed at the similar level, drilling vertical and curve sections of the horizontal wells in the Niobrara shale unconventional play posed additional challenges: – Rotating the BHA in the vertical section with a high AKO angle – Dealing with formation challenges – Holding the toolface to achieve consistent BUR in the curve – Completing the vertical and curve sections in one run The introduction in 2013 of the latest-generation steerable motors (LGSM) with further reduced short BTB distance design helped the operator overcome these challenges. The new system significantly improved drilling performance with excellent directional control. This paper will discuss the design, testing and results of horizontal wells drilled using the LGSM in the Niobrara unconventional shale play.

The demand for reduced AFEs for horizontal wells drilled in the Niobrara unconventional shale play increased the need for improved drilling efficiencies. Better efficiencies can be achieved by utilizing monobore well designs which maintain a single diameter hole size for the vertical, curve and lateral sections, eliminating the need for an intermediate casing string and the subsequent need to change out drilling assemblies for a reduced hole size. Positive displacement motors (PDM) with short bit-to-bend technology (SBTB) enable the well to be completed with a single conventional drilling assembly. To drill monobore wells in a single run, the following solutions were implemented: A positive displacement motor with SBTB and reduced adjustable kick-off (AKO) angle to achieve planned build-up rates and prevent component damage.Optimal motor output torque and speed for desired rate of penetration (ROP) and bit life.Drillstring and bottomhole assembly designed for improved drilling mechanics.Optimized drilling fluid program to maintain wellbore stability in challenging formations. Each solution enablesfor the monobore wells to be drilled in a single run, which decreases the days on well by reducing time spent running intermediate casing and tripping for drilling assemblies. This paper compares the monobore well design to the original well design utilizing multiple hole sizes by studying build-up rates (BUR), days on well, ROP and time spent tripping. The dataset used for this study comprises six single- conventional assembly monobore wells and six representative multiple-hole size wells. A consistent drilling efficiency improvement was apparent in the comparison. This paper shows in detail how short bit-to-bend motor technology is an innovative solution to drilling the Niobrara unconventional shale play with a single conventional assembly.