Schlumberger

High Drilling Efficiency in Shale Formations

Date: 04/21/2011

Spear shale-optimized steel-body PDC drill bit

At the March 2011 SPE/IADC Drilling Conference and Exhibition in Amsterdam, Smith Bits introduced a new drill bit designed specifically to improve economics in shale plays. The unique characteristics of the steel bit body make it possible for Spear technology to overcome hydraulic challenges, maximize hole cleaning, improve directional response, reduce borehole tortuosity, and enhance stability.

Unlike conventional polycrystalline diamond compact (PDC) bits that target either curve or lateral sections, the Spear shale-optimized steel-body PDC drill bit efficiently drills both curve and long lateral sections for faster penetration rates in low hydraulic energy environments.

Shale reservoirs

Shale reservoirs are usually drilled with long horizontal sections that are subsequently fractured to create flow paths in the low-permeability formations. This long lateral drilling with conventional PDC bits results in premature bit failure and short runs because of bit balling, poor directional behavior, and loss of tool face control. Lack of hydraulic energy at the drill bit means that cuttings accumulate at the bottom of the well, impeding access to fresh rock and dramatically reducing the rate of penetration (ROP).

High ROP, improved directional control

The Spear bit makes efficient use of rig time, minimizes bit balling and short runs, improves ROP, and enhances directional control. High ROP is achieved through a combination of tall and thin blades, which provide a large area for cutting flow. A unique hydraulic design directs flow toward the cutter faces keeping them sharp and sweeping the cuttings away from the bottom of the hole and around the bullet-shaped body into the annulus.

To improve directional control, Spear technology uses small cutters, with no adverse affect on ROP. Large cutters have a substantial depth of cut that creates a higher instantaneous torque response and causes loss of toolface control.

Successful deployment in North America

Spear bits have been used successfully in the Bakken, Barnett, Marcellus, Haynesville, and Eagle Ford shale formations in North America. In the Marcellus shale, for example, the operator’s target ROP for drilling the horizontal leg was 50 ft/h. The Spear bit achieved ROPs in excess of 65 ft/h, a 30% improvement over the operator-set target.

In the Haynesville shale, the Spear bit consistently drilled the curve and horizontal sections in one run, setting a new Haynesville horizontal ROP record of 49.7 ft/h. Although a few faster lateral runs have been drilled, no other bit has drilled the entire curve and lateral sections at that rate. The improved performance saved rig time, reduced bit costs, and shortened time to production.

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