Baker Hughes Incorporated : Patent Issued for Three-Coil System with Short Nonconductive Inserts for Transient MWD Resistivity Measurements (USPTO 9588250)
The assignee for this patent, patent number 9588250, is
Reporters obtained the following quote from the background information supplied by the inventors: "This disclosure relates to the field of electromagnetic well logging. More specifically, the present disclosure is a method of reducing effects of conductive drill pipes on transient electromagnetic signals.
"Electromagnetic resistivity instruments can be used to determine the electrical conductivity of earth formations surrounding a wellbore. An important objective in Measurement-while-drilling (MWD) applications is the estimation of the distance from the drillbit to an interface in the earth formation that has a resistivity contrast across the interface. The interface may be a bed boundary and/or a fluid interface between a nonconducting fluid (such as a hydrocarbon) and a conductive fluid such as brine.
"In a typical transient induction tool, current in the transmitter coil drops from its initial value I.sub.0 to 0 at the moment t=0. Subsequently, measurements are taken while the rotating tool is moving along the borehole trajectory. The currents induced in the drilling pipe and in the formation (i.e. eddy currents) begin diffusing from the region close to the transmitter coil in all the directions surrounding the transmitter. These currents induce electromagnetic field components which can be measured by induction coils placed along the conductive pipe. Signal contributions due to the eddy currents in the pipe are considered to be parasitic since the signal due to these currents is much stronger than the signal from the formation. In order to receive a signal which is substantially unaffected by the eddy currents in the pipe, one can measure the signal at the very late stage, at a time in which the signals from the formation dominate parasitic signals due to the pipe. Although the formation signal dominates at the late stage, it is also very small, and reliable measurement can be difficult.
"In prior methods, increasing the distance between transmitter and receivers has been used to reduce the influence of the pipe and shift the dominant contribution of the formation to the earlier time range. Besides having limited resolution with respect to an oil/water boundary, such a system requires considerable length (up to 10-15 m). Such large distances are not desirable or convenient for an MWD tool.
"There is a need to reduce the parasitic signals cause by eddy currents in transient field signal detection methods without increasing a distance between transmitter and receiver. The present disclosure fulfills that need."
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "One embodiment of the disclosure is an apparatus for evaluating an earth formation. The apparatus includes: a carrier including at least one transmitting antenna and at least two spaced-apart receiving antennas configured to be conveyed in a borehole, the carrier including a conductive tubular and a non-conductive insert in the conductive tubular encompassing at least one of the at least one transmitter antenna and the at least two spaced-apart receiver antennas; and at least one processor configured to: estimate a value of a resistivity property of the earth formation using first and second transient signals produced by a first one and a second one of the at least two spaced-apart receiver antennas respectively responsive to a transient activation of the at least one transmitter antenna.
"Another embodiment of the disclosure is a method of evaluating an earth formation. The method includes: conveying a carrier including at least one transmitting antenna and at least two spaced-apart receiving antennas configured in a borehole, the carrier including a conductive tubular and a non-conductive insert in the conductive tubular encompassing at least one of the at least one transmitter antenna and the at least two spaced-apart receiver antennas; activating the at least one transmitter and producing first and second transient signals in a first one and a second one of the at least two receiver antennas respectively; and using at least one processor for: estimating a value of a resistivity property of the earth formation using the first transient signal and the second transient signal.
"Another embodiment of the disclosure is a non-transitory computer-readable medium product having thereon instructions that when executed by at least one processor cause the at least one processor to perform a method. The method includes: estimating a value of a resistivity property of an earth formation using a first transient signal and a second transient signal produced by a first one and a second one of at least two spaced-apart receivers on a carrier conveyed in a borehole responsive to an activation of at least one transmitter on the carrier, the carrier including a conductive tubular and a non-conductive insert in the conductive tubular encompassing at least one of the at least one transmitter antenna and the at least two spaced-apart receiver antennas."
For more information, see this patent: Itskovich, Gregory B.; Reiderman, Arcady. Three-Coil System with Short Nonconductive Inserts for Transient MWD Resistivity Measurements.
Keywords for this news article include: Electronics, Electromagnet,
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