On a floating vessel or rig, heave can cause severe disturbances in the returning mud flow from the marine riser into the Flow Line. This effect is due to the changing height of the outflow point of the marine riser with respect to the sea bed. Thus the heave can be considered a volumetric flow disturbance, which for short intervals in the heave cycle, can be several times greater than the pump flow making accurate measurement very difficult.
Roll and pitch can also have a disturbance effect the flow in the Flow lines, this depends on the length and the fall in the Flow Line and the way the levels in the tanks and pits are measured.
These environmental effects can at times obscure and make the task of measuring the flow even more difficult than otherwise. The common method of obtaining a sufficiently accurate measure is either by averaging over longer periods or to revert to static measurements. That is, to stop the pumping process which means that it is the dynamic content of the measurement that tend to be lost.
Unfortunately, it is this absence of precise dynamic content in the flow measurement that can make cross correlation techniques, using the heave information to predict the flow development, rather uncertain.
This paper outlines a prototype Flow Compensator System (FCS) with the objective to minimise the effect of heave and to provide an optimum measurement point of flow in and out of the well.
The paper goes on to discuss the initial design requirements, installation, field operation and performance of the prototype equipment, outlining the lessons learnt and their influence on the development of a FCS for general use.