FIELD: survey in boreholes or well, particularly for measuring depth or liquid level.
SUBSTANCE: method involves preliminarily securing downhole instrument to logging cable end so that the downhole instrument is spaced Lb distance from basic magnetic mark previously formed on cable armor; lowering downhole instrument in well or lifting thereof; detecting magnetic marks on moving cable by reading thereof with the use of reading apparatus; registering magnetic mark location on logging curve and calculating downhole instrument landing depth Li based on magnetic mark detection; determining cable movement direction V; arranging an assembly including connected in series demagnetization means, magnetic mark application means and reading apparatus along moving logging cable at well head, wherein the reading apparatus is spaced fixed distance ΔL from mark application means along cable and the assembly is arranged so that basic magnetic mark is initially located between demagnetization means and reading apparatus; fixing distance L0 between reading apparatus and downhole instrument landing depth reference point; demagnetizing logging cable armor entering into demagnetization means, wherein if reading apparatus detects magnetic mark on cable armor difference between Lb and L0 is taken as the downhole instrument landing depth Li; applying new magnetic mark on cable armor with the use of magnetic mark application means and taking this magnetic mark as the basic one, wherein value determined with the use of above calculated downhole instrument landing depth Li, distance L0 and fixed distance ΔL and information about logging cable movement direction is taken as the new Lb value; providing following calculation of downhole instrument landing depth Li with the use of the new basic magnetic mark and new Lb value; storing values corresponding to Lb, ΔL and L0 distances in signal form after determination or change thereof. In particular case prospective value of magnetic mark detection point displacement relative start thereof is determined and the determined value is additionally used for new Lb value calculation. Current cable movement direction may be compared with prospective one and the comparison results are used for downhole instrument landing depth Li with the use of Lb value. Device for above method realization comprises cable movement direction determination unit, assembly including the first demagnetization means, the first magnetic mark application means, reading means, the second magnetic mark application means and the second demagnetization means, as well as two commutators, OR circuit, memory unit and calculation means. Above components are arranged in series along cable length. The reading apparatus is spaced the fixed distance ΔL from both mark application means and is spaced the fixed distance L0 from downhole instrument landing depth reference point. The device may also have comparing unit, which compares current cable movement direction with prospective one.
EFFECT: increased accuracy of downhole instrument landing depth determination.
5 cl, 4 dwg
