Control method for use with a steerable drilling system
A control method for use with a steerable drilling system comprises the steps of inputting parametric model data representative of drilling conditions and using the data to determine achievable drilling directions.
1. A method of predicting the operation of a steerable drilling system comprising the steps of:
calculating an ideal reachability ellipse using the equations:
Build
=
W
build
*
[
WOB
-
meanWOB
meanWOB
]
+
R
build
*
[
ROP
-
meanROP
meanROP
]
+
P
build
*
[
Pressure
-
meanPressure
meanPressure
]
+
F
build
*
[
Flow
-
meanFlow
meanFlow
]
+
M
build
*
[
RPM
-
meanRPM
meanRPM
]
+
T
build
*
[
Torque
-
meanTorque
meanTorque
]
+
I
build
*
[
sin
Inc
-
mean
sin
Inc
mean
sin
Inc
]
+
K
B
*
[
BuildDemand
%
]
+
C
BT
*
[
TurnDemand
%
]
+
build
bias
and
Turn
=
W
turn
*
[
WOB
-
meanWOB
meanWOB
]
+
R
turn
*
[
ROP
-
meanROP
meanROP
]
+
P
turn
*
[
Pressure
-
meanPressure
meanPressure
]
+
F
turn
*
[
Flow
-
meanFlow
meanFlow
]
+
M
turn
*
[
RPM
-
meanRPM
meanRPM
]
+
T
turn
*
[
Torque
-
meanTorque
meanTorque
]
+
I
turn
*
[
sin
Inc
-
mean
sin
Inc
mean
sin
Inc
]
+
K
T
*
[
TurnDemand
%
]
+
C
TB
*
[
BuildDemand
%
]
+
turn
bias
inputting data representative of actual drilling conditions into a parametric model;
calculating predicted build and turn gain, cross-coupling and bias values to derive build and turn responsiveness values attainable under given operating conditions from the parametric model to produce a predicted reachability ellipse;
plotting the predicted reachability ellipse and ideal reachability ellipse on a diagram to compare the predicted build and turn responsiveness to the ideal response for one or more sets of operating conditions.
2. A method as claimed in claim 1 , wherein the model data includes data representative of at least one of: weight on bit, rotational speed, rate of progress, torque, pressure, inclination, dip and azimuth of bedding planes or other formation characteristics, hole curvature/gauge or other geometric conditions, bit type and condition, and errors in instrumentation readings.
3. A method as claimed in claim 1 , wherein an output signal is produced which is used to control a display on which the predicted reachability ellipse diagram is displayed to provide an operator with information for use in controlling the operation of the drilling system.