Measuring and testing – Borehole or drilling – Downhole test
Patent
1992-07-13
1993-09-21
Williams, Hezron E.
Measuring and testing
Borehole or drilling
Downhole test
166250, E21B 4400, G05D 1700
Patent
active
052458717
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a process for controlling a drilling operation.
During the drilling of an oil well, the motor of the drill-rod string, which is mounted on the surface, rotates at a constant speed of approximately 50 to 150 revolutions per minute. However, the friction generated between the drilling tool and the bottom of the well or between the rods and the wall of the well can cause slowdowns and indeed even periodic stops of the tool. Since the motor continues to rotate at one end of the drill-rod string during this time, the latter tends to twist about its longitudinal axis, until the force exerted is greater than the frictional effect braking the tool. At this moment, the drill-rod string is relieved and the tool begins to rotate again at speeds which can reach peak rotational speeds of the order of 150 to 400 revolutions per minute. Since wells often follow broken paths, contact between the casing and the wall of the well occurs somewhat frequently.
It is clear that the behaviour of the tool has an important effect on the progress of the drilling operation. It is therefore desirable that the foreman driller be warned of periodic instabilities in the rotational speed of the tool, so that he can modify the drilling parameters, namely the rotational speed of the motor, the weight exerted on the tool and the mud flow rate, and thus ensure optimum drilling.
SUMMARY OF THE INVENTION
The object of the present invention is, therefore, to provide a process for controlling a drilling operation, which makes it possible to supply a user in a simple way with data relating to the state of rotation of the rod.
To achieve this, the invention provides a process for controlling a drilling operation, during which a tool is set in rotation in a well by means of a drill rod, the process involving the following steps: continuous manner; this variation exceeds a predetermined threshold; predetermined theoretical period; to control the drilling operation.
BRIEF DESCRIPTION OF THE DRAWINGS
Other characteristics and advantages of the present invention will emerge more clearly from a reading of the following description with reference to the accompanying drawings in which:
FIG. 1 is a diagrammatic sectional view of a drilling assembly;
FIG. 2 is a logic diagram of some steps of the process of the invention; and
FIGS. 3A, 3B and 4 each show pairs of curves of torque and rotational speed .
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
As illustrated in FIG. 1, a drilling assembly comprises a mast 10 equipped in a way known per se with a hook 12, on which is suspended a drill-rod string designated as a whole by 14. The drill-rod string 14 comprises a drilling tool 16, drill stems 18 and drill rods 20 forming an assembly called a drilling casing. In the example illustrated, the drill-rod string 14 is set in rotation by means of a turntable 22. Any other device can be used. The turntable 22 is equipped with a rotational-speed sensor 24 and with a sensor 26 for detecting the torque exerted on the drill-rod string 14.
Starting from the data representing the rotational speed and the torque, it is possible, according to the invention, to carry out a detection of the periodic rotational instabilities.
For this purpose, the following steps must be performed:
ascertainment of the variation in the torque:
To see whether the torque variations during a given period of time are pronounced, the difference between the maximum torque and the minimum torque is determined and this result is divided by the average torque. If the result of this calculation is greater than 10%, it can be assumed that there are periodic instabilities in the rotational speed of the casing.
This step is represented in FIG. 2 by: ##EQU1##
A result lower than 10% implies a small torque variation which makes it possible to infer from this that there is no instability in the rotational speed of the casing. In this case, the process makes it possible to signal to the foreman driller that he can maintain the drilling para
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Henneuse Henry
Sancho Jean
Dombroske George M.
Societe Nationale Elf Aquitaine (Production)
Williams Hezron E.
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