Determination and Display of Apparent Resistivity of Downhole Transient Electromagnetic Data

摘要

Systems, devices, and methods for evaluating an earth formation. Methods may include inducing a current in the formation; measuring a time-dependent transient electromagnetic (TEM) signal induced by the formation responsive to the current; and estimating apparent resistivity values for each of a plurality of samples derived from the TEM measurement, wherein each sample corresponds to a discrete time window of the TEM measurement. Estimating the apparent resistivity values for each of the samples includes determining for each sample a simulated homogeneous formation that provides a best fit for the sample. The apparent resistivity values may be used to estimate distance to an interface. The apparent resistivity values or the estimated distance may be logged and the log displayed. The apparent resistivity values, the estimated distance, or the log may be used to conduct further operations in a borehole, including geosteering.

主权项

1. A method for evaluating an earth formation intersected by a borehole, the method comprising:
(a) inducing a current in the formation; (b) measuring a time-dependent transient electromagnetic (TEM) signal induced by the formation responsive to the current; (c) estimating apparent resistivity values for each of a plurality of samples derived from the TEM measurement, wherein each sample corresponds to a discrete time window of the TEM measurement.