Assessment of Viscoelastic Properties of Drilling Fluids and their Impact on Hole Cleaning Capacity in Horizontal Directional Drilling
Creators: Rodriguez Leon, Paula Lizeth 
Publisher: name: University of Alberta Library
Year: 2022

<p>Trenchless construction technologies are a group of construction methods that use strategies to minimize or eliminate surface excavation. Horizontal directional drilling (HDD) is one commonly used trenchless method and can be used HDD to install underground pipelines and conduits. Additionally, HDD is the preferred method when crossing water courses because it reduces the environmental damage that can be caused by conventional construction methods. During the HDD process, especially while drilling the pilot bore, a large volume of cuttings is produced. Efficient transportation of these cuttings to the surface—commonly known as the hole cleaning—is essential for the successful completion of the project. Inappropriate hole cleaning conditions can lead to several problems that may cause the failure of the HDD project. </p>

<p>Researchers have studied hole cleaning process in the oil and gas industry as well as in HDD in the past years, and there is a general consensus that annular velocity, i.e., the velocity of the drilling fluid in the annulus of the borehole, is the factor that most influences hole cleaning performance in both vertical and directional drilling. Nevertheless, maintaining a high annular velocity is not feasible in HDD projects due to the impossibility of having rig equipment that keeps a turbulent regime. Moreover, in cases where high annular velocity is reached, this may cause erosion and hole enlargement. Other factors that influence the hole cleaning process, such as the nature of the cuttings produced and operational parameters, might be difficult to control. Those factors are determined by formation characteristics, equipment facilities in the field, borehole trajectory design, and project budget. Therefore, the effect of the rheological properties of drilling fluid on hole cleaning capacity was chosen as the major focus of this study. In particular, the elastic properties of the drilling fluid are studied, which are seldom included in the hole cleaning assessment. </p>

<p>The experimental program consisted of conducting rheological tests on water-based drilling fluids using an oscillatory rheometer (DSR). The drilling fluid additives investigated included partially hydrolyzed polyacrylamide (HPAM, two different grades) and sodium bentonite. The Bingham-Plastic model, Power-Law model, and Herschel-Bulkey model were applied to characterize the drilling fluids. The viscoelastic behavior of each sample according to its concentration and molecular weight has been determined, as well connecting the viscoelastic properties of the drilling fluid and indicators of hole cleaning capacity.</p>

<p>The major findings based on experiments with HPAM can be summarized as follows. First, the solution that gave the best hole cleaning performance had a molecular weight of 8 million Dalton at the highest concentration investigated (0.1%). Second, in most solutions, elastic behavior dominated over viscous behavior. Third, viscosity benefits hole cleaning while elasticity lowers the hole cleaning performance. The experiments with bentonite as a drilling fluid additive indicate that increasing the bentonite concentration increases the elastic and viscous component and improves hole cleaning performance. In addition, increasing the bentonite concentration causes the rheological parameters (such as the yield point (YP), the plastic viscosity (PV), the yield stress (τ_y), and so on) to increase, and flattens the velocity profile, which is also beneficial for the hole cleaning performance. The main conclusion of this study is that viscosity and elasticity each play a role in drilling fluid and both parameters should be included for an accurate assessment of hole cleaning performance.</p>