Overcoming Challenges of Drilling High-Dogleg-Severity Curves
Authors: Denney Dennis 
Published: February 2015

This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper SPE 139773, ’Overcoming Challenges for Drilling High-Dogleg- Severity Curves,’ by S. Janwadkar, SPE, O. Hummes, SPE, A. Peter, M. Freeman, SPE, and S. Privott, SPE, Baker Hughes; D. Greene, SPE, SM Energy; and C. Loesel, SPE, Forest Oil, prepared for the 2011 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 1-3 March. The paper has not been peer reviewed.

Drilling a high-dogleg-severity (DLS) curve maximizes the length of the later-al in the productive zone. Wells in shale-gas plays and other unconventional resources in the USA require a DLS of 10–14°/100 ft. Achieving high DLS with steerable motors presents many drilling challenges. Rotating a steerable motor with high adjustable-kickoff (AKO) -subassembly settings could result in fatigue failure. Alternatively, drilling in slide/rotate modes reduces drilling efficiency, increases tortuosity, and limits well placement in the productive zone. Use of closed-loop control and a short steering sleeve that decouples steering functionality from drilling dynamics can enable a system to drill high-DLS curves and extended-reach laterals with precise well placement and improved borehole quality.

Introduction

Drilling high-DLS curves can increase lateral length by several hundred feet, enabling additional hydrocarbon recovery. The ability to drill all sections with one system and eliminate slide drilling reduces drilling time significantly and eliminates trips to change the bottomhole assembly (BHA). Minimizing wellbore tortuosity enables setting casing easily and quickly and enables early production. Minimized tortuosity in the lateral also enables faster drillout of completion plugs with coiled tubing. The geology of the Eagle Ford shale in south Texas and of the Granite Wash tight sands in the Texas panhandle presents many challenges. Two operators had faced several problems while drilling in La Salle and Webb counties of south Texas and in Wheeler and Hemphill counties of the Texas pan-handle. Extreme geological complexities posed several drilling challenges.

Drilling and Completion Challenges

The major challenges for drilling and completing high-DLS curves and extended laterals in the Eagle Ford shale play and the Granite Wash are as follows.

Difficulty controlling the steerable-motor tool face and keeping the well trajectory as planned

Inconsistent build rates in the curve, requiring higher bend/AKO-subassembly settings

High bend and AKO-subassembly settings with conventional-motor drill-ing assemblies, limiting the drillstring rotational speed

Excessive time spent in slide drilling

Inefficient transfer of weight to the bit

Unacceptably low penetration rates

High torque and drag caused by a tortuous wellbore

High friction while drilling out plugs during the completion phase for Eagle Ford wells—adding lubricants helped reduce friction, which helped drill out the plugs successfully but increased the completion cost

Extra days required to drill and complete wells, resulting in excessively high drilling and completion costs