Patent ID: 6289596
Filing Date: 2001-09-18
Classification: E21B,G01C

Abstract:
A downhole drift indicator comprising:a housing for location in a drill string and defining a passage for drilling fluid;a restriction body defining a series of flow restrictions in the passage;a restriction member for co-operating with the flow restrictions to define a restricted flow area when located adjacent one of the flow restrictions, said restriction member being movable in one direction relative to the housing under the influence of the flow of drilling fluid through the passage, towards a first position;return means for biassing the restriction member in the other direction, towards a second position; anda drift responsive member being movable relative to the housing and the restriction member and pivotally connected to the restriction member, the pivot connection including a pivot member connecting the restriction member and the drift responsive member, wherein on the pivot connection being subject to a predetermined load, surfaces of the restriction member and drift responsive member engage to limit the load experienced by the pivot member,the degree of movement of said drift responsive member in said other direction from a respective first position being related to the inclination of the housing, the arrangement being such that, in use, reducing the flow of drilling fluid through the passage results in movement of said restriction member in said other direction from said first position until arrested by the drift responsive member, and restarting the flow of fluid resulting in movement of said restriction member from the arrested position towards said first position, the reduction in flow area resulting as the restriction member passes each flow restriction producing a pressure pulse in the drilling fluid, which pulse is detectable at the surface, the number of pulses indicating the degree of drift.