Design of an automatic drilling fluid measurement setup and closed-loop pH control

Abstract

This thesis concerns the design and construction of an automatic drilling fluid measurement setup and the use of such setup to control the drilling fluid pH. The construction of the experimental setup include modifications to the acquired rheometer to obtain reliable batch rheology measurements within the typical viscosity range of a shear-thinning drilling fluid ([0.02-0.15]Pas). A model-based control approach is taken to control the drilling fluid pH. With help of a static model we have defined a new scaling method which enables us to get an estimate of the required control fluid to shift the pH up to a mud volume of 32L. Implementation of the model shows that the pH can be maintained within the desired operating window if the quantity of control fluid is adjusted properly. The right quantity of control fluid is achieved by adjusting the estimated quantity of control fluid with help of a tuning parameter a. Results of this thesis show that to be able to control the pH at rig-scale, which is a dynamic process, closed-loop pH control based on the flux in and out of the mud tank should be implemented. The closed-loop pH control utilizes two pH sensors, the new scaling method and the signal from the Coriolis flow meter to add the right quantity of control fluid to stabilize the pH of the drilling fluid into the well. Based on the results that show the advantages of measuring both incoming and outgoing fluid properties at the active mud tank, a twin skid construction for rig-scale implementation is proposed. ?