MODELING OF BOREHOLE PRESSURES DEVELOPED DURING HDD

摘要

Horizontal Directional Drilling (HDD) is a proven trenchless construction method for therninstallation of underground utilities and pipelines. Subsequently, HDD is becoming widelyrnaccepted as a cost-effective alternative to traditional open-cut construction. The occurrence ofrnhydraulic fracturing, resulting in the migration of drilling fluid to the surface has placed the HDDrnprocess under scrutiny, especially when being considered for environmentally sensitive projects.rnHydraulic fracturing results from an excess buildup of fluidic pressure within the borehole.rnModels have been developed to predict borehole pressures; however, there is limited informationrnavailable on the properties of drilling returns obtained during HDD. A research program wasrnundertaken to model and determine flow characteristics for drilling returns under a variety of soilrnconditions and bore penetration rates. Nine soil samples were gathered based on the Unified SoilrnClassification System (USCS) and their respective rheological properties were obtained forrndifferent drilling fluids and target slurry densities. Additionally, the progressive gel strengths forrneach slurry were tested to investigate how interrupting an HDD project for an extended period ofrntime may increase the chance of hydraulic fracturing. This paper presents a comparison andrnanalysis of the predicted borehole pressures providing recommendations for contractors whenrnattempting installations in various geological formations. The result of this research is arnsimplified approach for predicting borehole fluid pressures for a wide range of projectrnparameters that can be used as a guide to minimize the occurrence of hydraulic fracturing.