This disclosure describes a blended buoyancy oil well survey instrument. An oil well survey instrument in a closed cylindrical housing having a specific gravity greater than the drilling mud in which it is used is modified in buoyancy by attaching one of several identical elongate cylindrical hollow containers or cylinders to it. They are filled with light material. They are made sufficiently strong that they do not collapse at working pressures. The cylinders are provided with upper end and lower end threaded stub shafts and mating receptacles to thread together thereby providing a modified buoyant system. The method is concerned with adjustment of the buoyancy so that the rate of fall is modified; in conjunction with mud flow velocity in the drill string, the buoyant descent of the instrument is controlled to about 100 or 200 feet per minute.
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