Pathfinder Energy Services, Inc.

Other

W-h Energy Services, Inc.

S Mark Haugland

A technique of estimating electrical parameters of an earth formation accounts for spatial inhomogeneities and frequency dispersion. The results are achieved using a model which is evaluated to generate predicted values for a plurality of electrical signals measured in a borehole in an earth formation as a function of a first set of model electrical parameters, a second set of model electrical parameters and model spatial coordinates of boundaries between regions of the earth formation. Transformations are applied to the measured electrical signals and the predicted values. The electrical parameters and spatial coordinates are selected to cause approximate agreement between the transformed measurements and the transformed predicted values. In some embodiments, the first set of electrical parameters is a set of conductivity values; the second set of electrical parameters is a set of dielectric constant values; and the spatial coordinates define regions of the earth formation where different values for the conductivity and dielectric constant apply.

Method of determining resistivity and/or dielectric values of an earth formation as a function of position within the earth formation

An azimuthally sensitive electromagnetic measurement tool is provided. The tool may be suitable, for example, to measure azimuthal variations of electrical properties of a subterranean formation. The tool includes a transmitter disposed to transmit electromagnetic energy into a subterranean formation and a longitudinally spaced receiver. At least one of the transmitter and the receiver includes a sector antenna. The sector antenna includes an exposed length of antenna wire that forms an arc about a portion of a circumference of the tool body. In one exemplary embodiment, the receiver includes first and second sector antennae, which, in combination, subtend a circular angle of about 360 degrees about the circumference of the tool body without substantially overlapping one another.

Azimuthally focused electromagnetic measurement tool

Method and apparatus are provided for adjusting electromagnetic well logging data for effects of frequency dispersion. In exemplary embodiments, a model is provided for estimating an electrical property of an earth formation as a function of frequency. The model is derived, for each particular volume of interest, based on measured data obtained by employing a plurality of interrogation frequencies. Measured data may include electrical properties of the volume of interest such as conductivity and dielectric constant. The model predicts the measurements expected to be obtained by a tool employing a selected interrogation frequency, including frequencies for which no measured data are available. In one embodiment, the model may be used to adjust measured data for effects of frequency dispersion to correspond to a selected interrogation frequency, allowing the adjusted data to be more effectively correlated to logging data obtained by a different type of tool employing a different interrogation frequency.

Adjustment for frequency dispersion effects in electromagnetic logging data

A resistivity measurement technique estimates a first value for a first electrical parameter consistent with an assumption that each property of a measured electrical signal senses the first electrical parameter and a second electrical parameter in substantially the same volume and estimates a second value of the first electrical parameter consistent with the estimated first value and consistent with each property of the measured electrical signal sensing the first electrical parameter and the second electrical parameter in different volumes. Applying this technique, a phase conductivity may be determined from only a phase shift measurement. An attenuation conductivity may then be determined based on an attenuation measurement and the phase conductivity. Since bandwidth is limited in data telemetry to an earth surface while drilling, phase shift measurements can be telemetered without attenuation measurements for accomplishing resistivity measurements.

METHOD OF DETERMINING RESISTIVITY OF AN EARTH FORMATION WITH PHASE RESISTIVITY EVALUATION BASED ON A PHASE SHIFT MEASUREMENT AND ATTENUATION RESISTIVITY EVALUATION BASED ON AN ATTENUATION MEASUREMENT AND THE PHASE SHIFT MEASUREMENT

Techniques are provided to transform attenuation and phase measurements taken in conjunction with a drilling operation into independent electrical parameters such as electrical resistivity and dielectric values. The electrical parameters are correlated with background values such that resulting estimates of the electrical parameters are independent of each other. It is shown an attenuation measurement is sensitive to the resistivity in essentially the same volume of an earth formation as the corresponding phase measurement is sensitive to the dielectric constant. Further, the attenuation measurement is shown to be sensitive to the dielectric constant in essentially the same volume that the corresponding phase measurement is sensitive to the resistivity. Techniques are employed to define systems of simultaneous equations that produce more accurate measurements of the resistivity and/or the dielectric constant within the earth formation than are available from currently practiced techniques.

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Houston, TX, United States of America

S Mark Haugland