The use of electromagnetic measurements in prior art downhole applications, such as logging while drilling (LWD) and wireline logging applications is well known. Such techniques may be utilized to determine a subterranean formation resistivity, which, along with formation porosity measurements, is often used to indicate the presence of hydrocarbons in the formation. Moreover, azimuthally sensitive directional resistivity measurements are commonly employed e.g., in pay-zone steering applications, to provide information upon which steering decisions may be made.
Downhole electromagnetic measurements may be inverted at the surface using a formation model to obtain various useful formation parameters. However, a large number of formation and wellbore properties are known to affect the electromagnetic measurements, for example, including horizontal and vertical resistivities, the resistivity of and distance to a remote bed, relative dip angle, dip azimuth direction, drilling fluid resistivity, borehole diameter, tool eccentering distance, and the tool eccentering azimuth angle. Finite element modeling indicates that the electromagnetic measurements depend on the above parameters in a highly complicated manner such that obtaining an accurate inversion tends to be problematic.
USPTO Backgrounds
USPTO Backgrounds