Initial Experimental Study on Formation of Filter Cake in Sand during Horizontal Directional Drilling

摘要

One of the major concerns associated with horizontal directional drilling (HDD) operations in sandy soils is keeping the borehole stable. Circulating drilling fluid inside the bore develops annular pressure counteracts the ground overburden pressure. While the infiltration of drilling fluid during circulation increases the excess pore water pressure around the bore which thereby decreases the effective stress of the soil medium, hydraulic fracture may consequently occur and disturb the stability of the bore. In this respect, the bentonite-based drilling fluid has been used during HDD to improve the formation of the cake around the bore, reduce the loss of circulation, and stabilize the borehole. This initial study investigates the impact of infiltrating 2%, 3%, and 4% bentonite in drilling fluid on both the formation of the cake in a sand medium and the shear strength parameters of the sand. To simulate the cake formation in the borehole during HDD, drilling fluid has been injected into the sand specimen using a pump while the specimen has been confined in a triaxial cell. Accordingly, the permeability and shear strength of the specimen have been measured. The experimental results show that when using drilling fluid with 2%, 3%, and 4% bentonite, further infiltration of the drilling fluid is prevented due to the formation of the cake at the bottom of the specimen. The results also show that the infiltration of the drilling fluid hardly changes the shear strength of the sand due to the negligible amount of bentonite trapped in the specimens.