Early detection of fluid influx from the formation (generally known as a "kick") is a key consideration for rig safety. The first indication of many kicks is given by a comparison of flow-in and flow-out of the well being drilled. Accurate flow measurement is therefore of crucial importance to the drilling industry. The heave motion of a floating rig, however, produces large instantaneous variation in flow-out. These fluctuations can simply be averaged over several heave periods but this leads to a delay in detecting an influx.
This paper describes a new approach to obtain an improved flow-out indication by utilising measurements of rig movement in order to predict expected flow variations. This information is used to adaptively compensate flow-out readings from existing sensors for the effects of rig motion to provide a more accurate measure of the instantaneous flow from the well. The technique has been incorporated in a drilling contractor's computerised monitoring and alarm system which displays the compensated measurements in realtime and automatically warns the driller and other key personnel of any influx or loss.
Field examples are presented to illustrate the effectiveness of the system and to show that a reliable alarm warns of changes in flow-out before they would normally be apparent with existing detection systems.