Technology Focus: Drilling Technology (February 2011)
Authors: Menand Stephane 
Published: February 2015

Technology Focus

Unconventional gas, especially shale gas, has generated strong interest recently. Much has been written on shale gas regarding stimulation and fracturing technology, environmental issues, geology, water management, reservoir permeability, gas recovery, and more, but far less has been presented about shale-gas drilling. I am taking this opportunity to write about shale-gas drilling because drilling technology and efficiency contribute to making shale-gas wells even more economical. Shale-gas plays are an excellent place and application where bottomhole-assembly (BHA), drillstring, well-trajectory, and bit-design optimizations play a great role in well economy. Indeed, because the number of horizontal wells drilled is numerous, a small reduction in drilling costs and nonproductive time could result in major cost savings for operators.

Whichever US shale-resource basin (e.g., Barnett, Fayetteville, Haynesville, Marcellus, and others) is studied, most of the wells drilled today are horizontal, enabling increasing the production rate significantly compared with vertical wells. These horizontal wells usually comprise a vertical, a curved, and a horizontal section. Depending on the shale basin, vertical depth ranges from approximately 500 to 3000 m, and the lateral horizontal section may be as long as 3000 m. The first challenge is designing a bit that can drill abrasive sandstone or limestone stringers (unconfined compressive strength up to 170 MPa) and soft shale efficiently, while keeping good bit steerability and durability.

Steerability is a great concern because build rate, up to 12°/30 m, must be reached to maximize horizontal length and, as a consequence, reservoir exposure. These high build rates may be attained by use of steerable mud motors or by some rotary-steerable system specially designed for high-dogleg applications. In shallow horizontal shale-gas wells, the challenge concerns the drillstring design because buckling becomes an issue. Indeed, to reach an acceptable rate of penetration, sufficient weight should be available on the bit without exceeding the critical buckling loads. Therefore, some inverted BHAs are proposed that contain heavyweight drillpipe, or drill collars above drillpipe, to help transfer the weight downhole.

With the numerous wells forecasted in the near future, drilling techniques in shale-gas wells will become well established, and drilling efficiencies will continue to improve.

Drilling Technology additional reading available at OnePetro: www.onepetro.org

SPE 128916 “An Intelligent System To Detect Drilling Problems Through Drilled-Cuttings-Returns Analysis” by A.N. Marana, So Paulo State University, et al.

SPE 135587 “The Effect of Drillstring Rotation on Equivalent Circulating Density: Modeling and Analysis of Field Measurements” by Ramadan Ahmed, University of Oklahoma, et al.

SPE 134306 “Numerical Simulation on Three-Layer Dynamic Cuttings-Transport Model and Its Application to Extended-Well Drilling” by Zhiming Wang, SPE, China University of Petroleum, et al.

SPE 134488 “Downhole-Vibration Measurement, Monitoring, and Modeling Reveal Stick/Slip as a Primary Cause of PDC-Bit Damage in Today’s Applications” by L.W. Ledgerwood III, SPE, Baker Hughes, et al.