Investigations of Transient Behaviour for non-Newtonian Fluid in a Vertical Well

• Main Author: Tlais, Mohamad Jawad
• Format: Dissertation
• Language: English

One of the most important factors in well-drilling operations is the accurate calculation of friction pressure loss. The accuracy of calculating this factor directly affects the management of bottom hole pressure and erosion control. This thesis investigates the effects of non-Newtonian fluid on pressure pulses during well-drilling operations. This investigation is mainly performed in scenarios such as pump shutdown and restart, and their behaviors are compared with the Newtonian fluid. For this purpose, a transient flow model based on the Advection Upstream Splitting Method (AUSMV) is implemented. In this study's first step, different rheological models are evaluated using experimental data and mathematical modeling. These models are the Newtonian, Bingham plastic, power law, and Herschel-Bulkley. This evaluation aims to determine the most accurate representation of shear stress-shear rate relationships in drilling fluids. In this regard, the Herschel-Bulkley full-range model is identified as the most accurate model for representing the mentioned relationship. Friction pressure loss calculations are also accomplished for Newtonian and non-Newtonian fluids (Herschel-Bulkley), and it is observed that non-Newtonian fluids experience more frictional losses. In addition, this study highlights the need for a smoother transition representation of the transition stage from laminar to turbulent flow transition in non-Newtonian fluids. This study significantly contributes to the field by integrating an improved non-Newtonian annular pressure loss model with a transient drift flux model using the AUSMV scheme. This improved model addresses zero and negative flow inaccuracy and introduces an exponential smoothing function to eliminate the discontinuity at zero flow rate in non-Newtonian fluids without deviating from the true friction loss values. Comparative studies using AUSMV and taking advantage of simulations focus on investigating bottom-hole pressure variations and pressure pulse behaviors. The results show that the non-Newtonian fluid faces higher friction losses than the Newtonian fluid. At the same time, its ability to neutralize pressure pulses is proven more effective. The implications of the improved friction model for reducing pressure pulses are fully demonstrated, which significantly increases the accuracy and reliability of drilling operations.