Assessment of drilling conditions

• US 4,685,329 A
• Filed: 05/02/1985
• Issued: 08/11/1987
• Est. Priority Date: 05/03/1984
• Status: Expired due to Term

• Current Assignee: Anadrill Incorporated
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Burgess, Trevor M.
• Primary Examiner(s): NOT, DEFINED
• Assistant Examiner(s): Oldham, Scott M.
• Application Number:
  US06/730,695
• Time in Patent Office: 831 Days
• Field of Search: 73/151/151.5, 73/152, 175/39, 175/40, 364/422
• US Class Current: 73/152.44
• CPC Class Codes: E21B 12/02 Wear indicators
• CPC Class Codes: E21B 44/00 Automatic control systems specially adapted for drilling operations, i.e. self-operating systems which function to carry out or modify a drilling operation without intervention of a human operator, e.g. computer-controlled drilling systems; Systems specially adapted for monitoring a plurality of drilling variables or conditions
• CPC Class Codes: E21B 49/003 by analysing drilling variables or conditions E21B49/005 takes precedence; systems specially adapted for monitoring a plurality of drilling variables or conditions E21B44/00

Abstract

In a method of assessing drilling conditions during a drilling operation measurements of torque applied (TOR), weight on bit (WOB), rate of penetration (ROP), and rotation speed (ROT) are gathered. Computed therefrom is a history (60, 61) of points (x, y) where x=(TOR/WOB) and y=(ROP/ROT).sup.γ : γ being a derived constant indicative of down hole geometry. Trends in this history are monitored to assess drilling conditions. For example in soft plastic rock migration 62 towards the origin and in hard plastic rock migration 63 towards the abscissa is indicative of drill bit wear.

Claims

1. A method of assessing drilling conditions during a hole drilling operation including the steps of:

gathering measurements of torque applied (TOR), weight on bit (WOB), rate of penetration (ROP), and rotation speed (ROT);

computing the values x=(TOR/WOB) and y=(ROP/ROT).sup.γ

for substantially simultaneous samples of TOR, WOB, ROP and ROT;

where γ

is a constant indicative of down hole geometry, building up a history of a plurality of points (x,y) in the (TOR/WOB) versus (ROP/ROT).sup.γ

plane; and

monitoring trends in the history of points (x, y).

2. A method of assessing drilling conditions as claimed in claim 1 and including the additional steps of:

computing values a=log (TOR/WOB) and b=log (ROP/ROT) for substantially simultaneous samples of TOR, WOB, ROP and ROT;

building up a first history of a plurality points (a,b) in the log (TOR/WOB) versus log (ROP/ROT) plane, and

interpreting the first history to identify the constant γ

.

3. A method of assessing drilling conditions as claimed in claim 2 and including the step of standardizing the points (x, y) for varition in WOB.

4. A method of monitoring drilling conditions comprising the steps of:

measuring the torque required to rotate the bit (TOR), the weight on the bit (WOB), the rate of penetration (ROP), and the speed of rotation of the bit (ROT);

calculating the values X=TOR/WOB and Y=(ROB/ROT).sup.γ

, where γ

is a constant indicative of downhole geometry;

building up a history of a plurality of points (X,Y) in the (TOR/WOB) versus (ROP/ROT) plane; and

from the direction the points X, Y take with respect to the origin as drilling progresses, monitoring a decrease in at least one of the values X and Y.

5. The method of claim 4 further including the steps of determining the slope of a line in a plot of log (TOR/WOB) and log (ROP/ROT) for a plurality of substantially simultaneously measured values of TOR, WOB, ROP, and ROT;

and using said slope of the line as the exponent γ

.

6. A method of assessing drilling conditions comprising the steps of:

measuring the torque required to rotate the bit (TOR), the weight on the bit (WOB), the rate of penetration (ROP), and speed of rotation of the bit (ROT);

for substantially simultaneous reading of TOR, WOB, ROP, and ROT, plotting log (ROP/ROT) versus log (TOR/WOB);

determining a quantity γ

equal to the slope of a straight line through the points in the plot of log (ROP/ROT) versus log (TOR/WOB);

plotting a plurality of points (X,Y) where X=(TOR/WOB) and Y=(ROB/ROT).sup.γ

;

monitoring a decrease in the value of at least one of the values X and Y, and

pulling the bit when the decrease is substantial.