Optimization of Drilling Fluid Flow Rates – A Study of the Drilling Fluid Flow rates and Annular Pressure in Horizontal Directional Drilling
Creators: Li, Bingxuan
Publisher: name: University of Alberta Library
Year: 2023

<p>Trenchless technologies have experienced the fast development and dramatic change in the past three decades. Derived from oil and gas industry, Horizontal Directional Drilling (HDD) is considered as one of the most rapidly expanded trenchless technologies and widely used in infrastructure construction and pipeline installation, minimizing the social, environmental, and economic cost compared with traditional open cut method. <br>
In the HDD, drilling fluid plays an important role in borehole integrity and cuttings transportation. However, improper drilling fluid management is directly related to several frequent problems in drilling process, including insufficient hole cleaning performance and hydro fracture. Excess drilling fluid flow rate will increase the borehole annular pressure, and further raise the risk of hydro fracture in the annulus, while low drilling fluid flow rate will affect the hole cleaning performance and lead to stuck pipe. Due to the HDD unique features such as large borehole diameter, highly inclined and horizontal borehole, previous models for drilling fluid management developed in oil and gas industry perform poorly in HDD project.<br>
To have a brief understanding of drilling fluid flow rate limitation, a comprehensive review was conducted. Annular pressure and hole cleaning performance were found to be the most important factors which restricted the drilling fluid flow rate. The Delft equation, which was considered as the widely accepted solution to estimate the maximum allowable pressure in the borehole, was analyzed to calculate the maximum flow rate along the drill path. Five different cuttings transport models were introduced and compared to quantify the minimum drilling fluid flow rate in the annulus. <br>
Among the five different models, Larsen’s model was employed to a case study to verify its feasibility and accuracy in HDD industry. Although Larsen’s model had some defects, it provided a reference value (critical transport fluid velocity) indicating when the cuttings stopped accumulating in the lower side of wellbore and roughly estimated the cuttings bed heigh when drilling fluid flow rate was relatively low. Overall, Larsen’s model had a high potential to become an indicator for hole cleaning performance<br>
Another case study was conducted to analyze the maximum flow rate change with the Delft Equation. The maximum flow rate raised to a peak point and decreased in the remaining drilling path. The peak point occurred when the increment of the maximum frictional pressure loss equaled to the frictional pressure loss gradient. The annular pressure easily exceeded the maximum allowable pressure near the entry and exit point, which meant that adequate reinforcement and casing were necessary in the exit and entry point. Most of the drill path (80%), drilling fluid could be circulated at 0.5 m/s and over half of the drill path (55%) drilling fluid could be circulated at 5 m/s. As a result, drilling fluid could be circulated at a dynamic flow rate in different sections of drill path, which would greatly improve the hole cleaning performance in the annulus.</p>