TABLE OF CONTENTS Direct circulation requires that the drilling fluid flow from the compressor, through the standpipe, through the rotary hose, through the swivel, down the inside of the kelly down the inside of the drillpipe and drill collars, and through the drill bit to the bottom of the hole. After entraining the cuttings at the bottom of the hole, the drilling fluid flows into the annulus between the outside of the drillstring and the inside of the borehole and flows the cuttings up the annulus to the blooey line at the surface where the cuttings are expelled into a pit. The boreholes can be vertical, slant, deviated and their combinations in configuration. This section describes the theory and procedure for determining the minimum required gas flow rate for drilling boreholes with different configurations.
Most water wells, monitoring wells, mining boreholes, and geotechnical boreholes are vertical boreholes. The percentage of deviated and horizontal wells in oil and gas recovery wells has been increasing rapidly since the 1980s. However, because of limitations of directional drilling tools such as measurement while drilling (MWD) in compressible fluid drilling, gas-drilling technologies are mostly used for vertical wells in the petroleum industry.
Borehole pressure. Equation (2.7) presents a relationship between volumetric gas flow rate and flowing borehole pressure based on minimum kinetic energy. The minimum required gas flow rate cannot be determined unless the flowing borehole pressure is known. The flowing borehole pressure can be formulated on the basis of the first law...
