Baker Hughes Corporation

Western Atlas International, Inc.

Baker Hugues Incorporated

Martin Townley Evans

Andrew Richard Burt

Volker Krueger

Matthias Gorek

Albert A Alexy

René N Ritter

Roland Edward Chemali

Paul E Pastusek

Friedhelm Makohl

Rene N Ritter

Stanley T Hewitt

Efraim Dory

Stanley Thomas Hewitt

A resistivity sub including a resistivity sensor forms part of a bottom hole drilling assembly. The sensor is maintained at a substantially fixed offset from the wall of a borehole during drilling operations by, for example, a stabilizer. In WBM, galvanic sensors may be used, with or without commonly used focusing methods, for obtaining a resistivity image of the borehole wall. In OBM, capacitive coupling may be used. The apparatus is capable of using other types of sensors, such as induction, MPR, shielded dipole, quadrupole, and GPR sensors. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b).

Apparatus and method for resistivity measurements during rotational drilling

A resistivity sub including a resistivity sensor forms part of a bottom hole drilling assembly. The sensor is maintained at a substantially fixed offset from the wall of a borehole during drilling operations by, for example, a stabilizer. In WBM, galvanic sensors may be used, with or without commonly used focusing methods, for obtaining a resistivity image of the borehole wall. In OBM, capacitive coupling may be used. The apparatus is capable of using other types of sensors, such as induction, MPR, shielded dipole, quadrupole, and GPR sensors.

A method and apparatus for obtaining a resistivity measurement of an earth formation surrounding a borehole in an MWD device uses an electrode for injecting current into the earth formation and an electrode for obtaining a responsive signal from the borehole. The electrodes are located on the drill bit arm or blade. Measured resistivity values are obtained at the location of the drill bit. Measurements can be taken in both oil-based mud and water-based mud environments. Maximum or minimum resistivity can be used to best represent the resistivity of the surrounding formation.

Formation resistivity measurement sensor contained onboard a drill bit (resistivity in bit)

An apparatus for obtaining resistivity images of a borehole includes an array of measure electrodes separated from a pad or the body of the instrument by a focusing electrode. The focusing electrode is maintained at a slightly higher potential than the measure electrodes. The apparatus is primarily intended for use with conducting fluids but may also be used with non-conducting fluids. A modulated electrical current with a carrier frequency of 1 MHz is injected into the formation. When used with a non-conducting fluid, capacitive coupling between the electrode and the conductive formation is provided by the dielectric of fluid. When used with a conducting borehole fluid, an additional capacitor may be incorporated into the circuit. The current in the measure electrode is indicative of the conductivity of the formation. To avoid cross-talk between conductors in an isolator section between the current source and the measure electrode, signals indicative of the measure currents are demodulated to a frequency of 1.1 kHz. This makes it possible to use the configuration of prior art devices designed for conductive coupling between the logging tool and the formation.

Apparatus and method for wellbore resistivity imaging using capacitive coupling

An apparatus for obtaining resistivity images of a borehole having an oil-based mud includes a rotating measure electrode on a measurement-while-drilling apparatus. A modulated measure current is capacitively coupled to the formation through the nonconducting mud. The electrode may be carried on a stabilizer of the drilling assembly. An extendable arm may be used to maintain a desired distance between the electrode and the formation.

Apparatus and method for wellbore resistivity determination and imaging using capacitive coupling

An apparatus for obtaining resistivity images of a borehole includes an array of measure electrodes separated from a pad or the body of the instrument by a guard electrode. The guard electrode is maintained at a slightly lower potential than the pad and the measure electrode is at an intermediate potential thereto. With this arrangement, the current from the guard electrode defocuses the measure current from the measure electrode as it enters the formation, and at greater distances, the current from the measure electrode is refocused by the effect of the current from the pad. This defocusing and refocusing defines a region of investigation away from the borehole wall that is relatively insensitive to borehole rugosity. Circumferential and vertical overlap may be obtained either by the arrangement of the measure electrodes, or by relying on the broadening of the measure beam as it enters the formation.

Image focusing method and apparatus for wellbore resistivity imaging

An instrument for measuring resistivity of earth formations within azimuthal segments. The instrument includes azimuthally separated measure electrodes placed in contact with the wall of a wellbore penetrating the earth formations. The electrodes are placed in contact with the wall by springs, hydraulics or similar mechanisms. A guard electrode surrounds each measure electrode. The instrument includes a booster current electrode axially spaced apart from the guard electrodes. An insulator axially separates the guard electrodes from the booster electrode. Monitor electrodes are disposed on the exterior of the insulator. A first bucking current circuit is connected to the guard electrodes. The first bucking current constrains the flow of measuring currents from each measure electrode to a path substantially perpendicular to the axis of the instrument. A booster current circuit is connected to the booster electrode. The booster current circuit is controllably operated to maintain substantially zero voltage drop across the monitor electrodes. The instrument includes first measuring current sources each connected to one of the measure electrodes, and circuits for measuring voltage and current emitted through each of the measure electrodes. The resistivity of the segment in contact with each measure electrode can be determined from the voltage and current. In a preferred embodiment, the lengths of the booster electrode, insulator and guard electrodes are selected to enable determination of resistivity without having symmetric flow of bucking currents about the axis of the instrument with respect to the measure electrodes.

Azimuthally segmented resistivity measuring apparatus and method

A method for concurrently gathering acoustic and resistivity data for mapping the texture of the sidewall of a borehole using a single imaging tool. The data are sampled, formatted and merged to provide a single composite image of the borehole sidewall.

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Norwich, United Kingdom

Martin Townley Evans