| 摘要 |
A discharge valve 34 and a use thereof in a drilling operation is described, enabling the operator to select an intermediate section of a well where the return flow of the drilling fluid is boosted without intervention from the surface. Fluid return is boosted by activation of said discharge valve in response to annulus fluid pressure, thus allowing fluid flow from the internal bore of the drill string, to the annulus between string and wellbore, increasing fluid volume and enhancing flow rate. On moving below said intermediate section, where annulus pressure is increased above a further threshhold, the valve is closed and fluid flow between bore and annulus stopped. The intermediate section can be, for example, a cased section of a well. |
