System provides new approach for directional drilling

Jan. 3, 2000
In collaboration with Japan National Oil Corp., Sperry-Sun, Houston, has designed a completely new approach for rotary steerable drilling.

In collaboration with Japan National Oil Corp., Sperry-Sun, Houston, has designed a completely new approach for rotary steerable drilling.

Click here to enlarge image

Using point-the-bit technology, the assembly steers the wellbore in any desired direction while rotating the drillstring.

Design

Click here to enlarge image

The technology utilizes a shaft that is mounted with bearings at each end (Figs. 1 and 2). The outer housing is free to rotate, but the speed of rotation is restricted to about 2 rotations/hr by an antirotation device.

Click here to enlarge image

The driveshaft is deflected midway between the bearings by a pair of eccentric rings through which the shaft passes. By rotating the rings, the shaft can be deflected to any desired toolface setting with varying degrees of offset from center.

The deflection of the shaft in the middle results in the deflection of the assembly, which carries the bit in the opposite direction. And the computer-controlled bias unit automatically detects the natural "roll" of the outer housing and compensates for this by correcting the ring positions in the opposite direction.

Because the tool works by pointing the bit, the technology can take advantage of the antispiraling action of long-gauge bits, minimizing the nonconstructive tendencies of bits that may have a strong side-cutting action. Subsequently, the rotary system should minimize both hole spiraling and wellbore tortuosity.

Applications

With the system (Geo-Pilot), two modes of rotary steering become possible. In the manual steering mode, the tool is pointed and controlled by a directional driller. In the automated mode, due out later this year, the system will drill along a preprogrammed trajectory.

Drillers prepare to run the rotary steerable system in the hole at the Gas Research Institute's facility in Catoosa, Okla. Tool length for the point-the-bit assembly is about 20 ft, excluding the drillbit and upper flex sub (Fig. 3). Photo courtesy of Sperry-Sun, Houston.
Click here to enlarge image

Since January 1999, the technology has undergone field trials at the Gas Research Institute's Catoosa test facility near Tulsa (Fig. 3). More recently, it has been used by Canadian, Norwegian, and US operators.

In Louisiana, for example, Spirit Energy 76 drilled a total of 7,825 ft with the system, achieving 4,505 ft in a single run. Spirit Energy says drillstring torque and drag fell to 66 and 41% of what was expected, respectively.

The rotary steerable system provides real-time continuous steering information with at-bit inclination measurements that assess wellbore trajectory. Additionally, it is fully integrated with logging-while-drilling sensors and Sperry-Sun's rig information system.