G - Physics – 01 – V
Patent
G - Physics
01
V
324/11
G01V 3/20 (2006.01) G01V 3/24 (2006.01) G01V 11/00 (2006.01)
Patent
CA 1278342
ABSTRACT The invention provides methods and apparatus for measurement of electronic properties such as the resistivities, polarization phenomena, and dielectric constants of geological formation and cement layers adjacent to cased boreholes. Current is passed from an electrode in electrical contact with the interior of the borehole casing to an electrode on the surface of the earth. Two or more pairs of voltage measuring electrodes which are in electrical contact with the interior of the casing provide at least two voltage outputs which are subtracted to provide a differential voltage output which in turn provides a measurement of the differential current conducted into formation in the vicinity of said electrodes. A calibration and nulling procedure is presented which minimizes the influences of variations in the thickness of the casing and in variations of electrode placements. A.C. currents passed from the downhole electrode to the surface electrode provide measurements of the resistivities of the adjacent geological formations. Such measurements also provide an indication of the presence or absence of cement exterior to the casing. Transient measurements of the differential voltage response to passage of transient current into formation provide measurements of polarization phenomena and the capacitance of the casing in contact with the geological formation which provides a measurement of the dielectric constant of the adjacent geological formation which in turn allows the computation of the amount of oil and gas in place if the porosity is known. Other transient measurements provide information concerning the lithological characteristics of the formation such as the presence or absence of clays. Measurements while drilling (MWD) can also be performed through the drill pipe attached to the drill bit in open holes.
550875
Smart & Biggar
Western Atlas International Inc.
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