Schlumberger Technology Corporation

Cyrille Levesque

David Lee Alumbaugh

Richard A Rosthal

Hong Zhang

Guozhong Gao

H Frank Morrison

Ping Zhang

Donald C McKeon

Dominique Benimeli

Methods and related systems are described for making an electromagnetic induction survey of a formation surrounding a cased section of a borehole. An electromagnetic transmitter and/or receiver are deployed into the cased section of the borehole. One or more additional devices are used to measure the properties of a conductive casing relating to conductivity, thickness and magnetic permeability. A casing coefficient is then calculated that can then be used for the processing of the deep-sensing induction measurements.

Measuring casing attenuation coefficient for electro-magnetics measurements

The present disclosure relates to determining the attenuation of an electromagnetic signal passing through a conductive material. An antenna is provided and placed in relatively close proximity to the conductive material. An alternating current is passed through the antenna and the impedance of the antenna is measured. The attenuation is determined using the measured impedance. A single frequency measurement may be made, or multiple measurements using different frequencies may be made. Grouped parameters based on properties of the material and the frequency of the current are used to relate the coil impedance to the attenuation. A current frequency for which the ratio of the antenna's resistive part of the impedance to the angular frequency of the current is substantially insensitive to at least one of the parameters is preferred.

Attenuation of electromagnetic signals passing through conductive material

Methods and related systems are described for analyzing electromagnetic survey data. Electromagnetic survey data of a subterranean formation is obtained using at least a downhole transceiver deployed in a borehole and a transceiver positioned on the surface, or in the same or another borehole. Limits are defined for casing correction coefficients that account for effects of the borehole casing. A constrained inversion process is performed solving for the casing correction coefficients within the defined limits, and for one or more parameters of a model representing attributes, such as resistivity, of the subterranean formation.

Analysis of subsurface electromagnetic data through inversion with constrained casing correction coefficients

The present disclosure relates to determining attenuation factors relating to an electromagnetic signal passing through, a conductive material seen by a real sensor. A sensor is provided and disposed proximate to the material. An alternating current is passed through the sensor and the impedance of the sensor is measured. The impedance of an ideal coil is obtained from the measured impedance using electromagnetic modeling combined with a circuit analysis of the coil impedance, and the attenuation factors for the real coil in straight or feedback mode are determined by electromagnetic modeling of casing attenuation factors and impedance of an ideal coil combined with equivalent circuit modeling of the sensor transfer functions. The attenuation factors seen by the real sensor may be determined in real-time or post-survey. The material may be magnetic or non-magnetic.

Correction factors for electromagnetic measurements made through conductive material

Body () for measuring the resistivity of a formation () surrounding a well () equipped with a lining (), comprising: a body () of a probe (), a set of three primary voltage measurement electrodes (ea, eb, ec), an upper electrode (ea) and a lower electrode (ec) and a central electrode (eb), two electrodes (In, In), an upper current injection electrode (In) and a lower current injection electrode (In) arranged on each side of the set of primary electrodes, characterized in that it also comprises, two secondary voltage measurement electrodes () arranged on each side of the set of primary electrodes (ea, eb, ec), and between the two current injection electrodes (In, In), the spacing between a secondary electrode () and the closest primary end electrode (ea, ec) being more than 1.5 times the spacing between the primary electrodes (ea, eb, ec).

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La Defense, France

Cyrille Levesque