Optimized Steerable Motor Design Overcomes Drilling Challenges in the Fayetteville Shale Unconventional Play

Abstract

The US-land unconventional shale plays have initiated an exponential increase in the number of horizontal wells drilled and completed in the last decade. Maximizing well productivity and improving drilling efficiency has always been a major challenge. Well placement in the sweet spot and extended laterals help maximize productivity. Curve intervals drilled with higher dogleg severity (DLS) have a reduced vertical-section which maximizes the length of subsequent lateral section in the productive zone. Wells in US shale plays are usually drilled with a DLS of 10 to 14 °/100 ft, but achievinghigh DLS presents numerous drilling challenges: rotating a steerable motor with a high adjustable kick-off sub (AKO) angle could result in bottomhole assembly (BHA) fatigue failure and premature damage to bit; drilling in oriented (slide) mode limits weight transfer to the bit which may reduce the rate-of-penetration (ROP). These challenges led to the development and successful testing of a new steerable optimized designmotor (ODM) with a short bit-to-bend (BTB) distance. In some cases, the ODM motor drilled all sections, including high-DLS curves, tangents and laterals with precise directional control and well placement with one BHA. The ODM has helped the operator to achieve higher DLS at lower AKO angle settings, enabled rotating the BHA in well profiles where previously used motors could be operated only in slidemode and maximized the length of curve interval drilled in rotary mode at higher RPMs. Drilling high- DLS curves increased the length of laterals, enabling additional recovery of gas. The new system significantly improved drilling performance with excellent directional control. This paper will discuss the design, modeling and results of horizontal type wells drilled using the steerable ODM in the Fayetteville Shale unconventional play.