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.