Page 186 - Practical Well Planning and Drilling Manual

Section 2 revised 11/00/bc 1/17/01 12:04 PM Page 162

[ ] Well Programming
2.3.1

Sideforce generating tools. The rebel tool is rarely run today. It is
positioned just above the bit and can be set up for a left- or right-hand
turn. It gives a gradual turn in the order of 1˚/100 ft as long as the hole
is in gauge. The tool has two arms or “paddles” linked by a steel rod.
The length of the paddles determines the direction of walk. It should
not be run where wellbore instability or balling is likely, since solids
will pack in around the paddles.
The principle of operation is that when long paddles are used, the
highest paddle hits the low side of the hole. The weight of the BHA sit-
ting on this paddle turns it in toward the center; this force is transmit-
ted along the rod to the paddle nearest the bit. When the upper paddle
is on the low side taking weight, the lower paddle pushes against the
right hand edge of the hole, exerting a sideforce to the left.
With the short paddles, when the upper paddle is on the low side
the lower paddle pushes against the left-hand edge of the hole, exert-
ing a sideforce to the right. Remember, Long paddles for Left turns.
A recent innovation from Baker Hughes Inteq, yet to be field proven
at the time of this writing, is a dynamically adjustable stabilizer. The
AutoTrak™ system uses an orientating sleeve that rotates relative to the
BHA but does not rotate relative to the hole. Expanding stabilizer pads
apply forces to the hole to continuously steer the tool. The system can
be controlled from the surface and can apparently be set up to auto-
matically geosteer within the reservoir—that is, using LWD measure-
ments to keep the borehole within a certain part of the reservoir.
Downhole positive displacement mud motors. Power applied
hydraulically downhole to the bit allows fine control of inclination and
azimuth when combined with steerable systems or bent subs. On some
tools the angle of the bend (and hence the dogleg severity) can be
adjusted downhole. Using an Andergauge adjustable stabilizer above a
straight motor also allows adjustment of build or drop performance.
Using downhole motors also requires careful attention to
hydraulics and bit selection. The tool will give a specified power output
and rotational speed for a given flow rate. This must be matched with
the possible ranges of pump outputs for the total system pressure loss
(including the motor) and the desired flow rate for hole cleaning. With
high-speed motors the turn speed should be compared to the maximum
recommended rotary speed for the bit, if a roller cone bit is used.

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