Title: A study on the accuracy of the modelled frictional pressure loss based on rheological characterisation of the drilling fluid
Description: During drilling operations, it is important to get a good understanding of the pressures in the well in order to have control of the drilling process and get a more efficient drilling program. Pressure calculation in the well is based on three components; hydrostatic pressure, frictional pressure and pressure due to acceleration. The pressure loss related to the friction is the component with the highest uncertainty and it is therefore important to get a better understanding of the uncertainties related to the modelling of this pressure. The frictional pressure loss is calculated based on the rheological properties of the drilling fluid. When deriving the rheological properties, there are different procedures, equipment and models used to model the frictional pressure loss during drilling. Depending on the method applied and assumptions made, the level of accuracy in the frictional pressures will vary.
Measurement of drilling fluid rheology is normally performed by Couette (also known as bob-in-cup) type instruments such as Fann 35 rheometers, where a series of measurements are performed for different rotational speeds in order to derive the rheological curve of the fluid. Such measurements are based on the assumption of an ideal unperturbed linear velocity flow profile, known as Couette flow. Inhomogeneities in the fluid, such as solids particles, cause perturbations to the flow.
The frictional pressure loss of the drilling fluid in the well is derived using the estimated velocity flow profile at the flow boundaries, i.e. drillpipe or annular walls, where no slip at the wall is normally assumed.
This study will compare the frictional pressure loss derived from the rheological characterization of a drilling fluid using an Anton Paar high-precision rheometer (shear dependent flow) with the actual pressure measured in a flow loop experiment (pressure dependent flow) and quantify the magnitude of the accuracy and discuss the main contributors to the uncertainties. Another aspect of this study will be looking at the effect of solids particles on the predictability of frictional pressure loss.
In this study, the rheological characterization of the drilling fluid will be made by reducing the shear rate logarithmically from 1000 s-1 to 0.01 s-1 while measuring shear stress using a high precision rheometer (Anton Paar MCR 302). The power-law rheological model will be fitted to the flow curve data and employed to develop the mathematical relation between flow rate and frictional pressure drop in drilling. The results will then be compare with experiments in a Flow-loop at the University of Stavanger (UoS) and alternatively several flow-loops at IRIS with different pipe diameter (to be determined).
Another aspect of the study is to better understand and hopefully explain what happens in the fluid by looking at the statistical mechanics/kinetics of the fluid/particles.
The rheometer measurements of the drilling fluids in this study will be conducted using an Anton Paar MCR 302 rheometer at the Department of Petroleum Engineering at University of Stavanger (UoS). The measurements will be performed at atmospheric pressures and tempeartures.
To ensure efficient and systematic testing of each fluid sample, automated testing sequence can be devised and setup in the measurement window of the software (RheoPlus© ver. 3.62 software).
Flow-loop experiments will be conducted in the multiphase laboratory at the University of Stavanger (UoS) using a horizontal pipe connected to a pump, flowmeter and two pressure transducers. Alternatively, it can be performed at IRIS on vertical pipes with different pipe diameter. The rates are to be determined based on the range of the flow curve.