Patent ID: 6026914
Filing Date: 2000-02-22
Classification: E21B

Abstract:
A method for determining the elevation at a survey point in a subterranean wellbore which is being drilled with a drill string which contains a continuous column of fluid having a known and substantially constant density, comprising:positioning a downhole tool in the drill string at the survey point, said tool carrying first means for measuring fluid pressure and being connected with second means for transmitting a signal which is indicative of the fluid pressure measurement to third means, located outside the wellbore, for calculating elevation of the survey point;providing fourth means for measuring fluid pressure at a reference point of known elevation, said fourth means being in pressure sensing communication with the column of fluid and being connected with fifth means for transmitting a signal indicative of the fluid pressure measurement taken at the reference point, to the third means;measuring the fluid pressure at the reference point and transmitting a signal indicative of the measurement to the third means;measuring the fluid pressure at the survey point and transmitting a signal indicative of the measurement to the third means; andcalculating the elevation of the survey point by applying the third means which uses the pressure measurements, the density of the fluid and the known elevation of the reference point.