Early detection of fluid influx from the formation into the wellbore during a drilling operation, generally known as a kick, is a major concerning for the safety of crew and rig equipment and, for the well itself. In the past, many well kicks have been observed at its very beginning by delta flow parameter which is simply the returned mud flow rate minus the circulating injected mud flow rate. Accurate flow measurements in this case are of great importance for the kick detection systems. When drilling from a floating rig, heave motion causes large instantaneous fluctuation in flow out from the well. It affects the delta flow measurement ant it is undesirable specially in deep water when kick detection is crucial. In the present work, many methods have been investigated as an attempt to overcome that problem. And, a new approach to obtain better delta flow indication is presented. Data has been recorded from a drillship in a real drilling operation. Discussions are carried out comparing the return flow rate of drilling mud onboard a floating drilling vessel and that obtained following the procedure here presented. Finally, a comprehensive state of the art is detailed and simulations of drilling operations illustrate an application with good results for identifying any delta flow change.
The problems observed in the influx from formation in floating drilling units has be motivated a great effort from researchers in order to obtain more precisely the net flow rate between mud flow rate injected and returned from the well. Moreover, variations of mud tank level should be detected accurately with minimum effects of the floating rig motions. Particularly drilling vessel vertical heave motion causes undesirable fluctuations in the returned mud flow rate. The quick detection of an influx from the formation into the well is a one of the key point in the crew safety.
In the present paper, a method to identify the mud flow rate fluctuations induced by the drilling vessel vertical (heave) motion is presented. The main purpose is to detect the difference between the returned mud flow rate from measurements of a mud-logging unit onboard and estimated mud flow rate with fluctuations due to heave motion. In this manner, it is possible to have that differential on mud flow rate more clear and reliable in order to identify early gain or loss of mud flow rate from or into the formation. Any deviation observed on above mentioned differential which exceeds a fixed safety range is considered an abnormality of the well and stand by procedure for rig and crew safety must be taken. As an example, a simulation and a measurement of returned mud flow in a drilling operation are compared. Results showing simulated situations of loss and gain of mud in a drilling operation are presented.
