Previous studies of resistivity anisotropy have neglected crossbedding effects. This article analyzes induction response in crossbedded reservoirs using a new computer modeling code. The code computes the response of an induction logging tool as it orthogonally traverses many beds, each of which possesses different crossbedding characteristics. The crossbedding in each medium is described by a uniaxial conductivity tensor whose principal axes have strike and dip angles oriented arbitrarily with respect to the bedding planes. The code is numerically efficient; response for a tool logging through several beds can be generated in less than 15 minutes on a modem workstation. Results show that, for anisotropy coefficients less than 5, computed responses for both two-coil and multicoil devices vary in a continuous manner as the sondes cross a single bed boundary separating two infinitely thick beds. Furthermore, after correction for skin effect, the limiting log values far from the bed boundary are entirely predictable from a previously published formula. However, in vertical wells, when the crossbedding dip angle is 75" or greater and the anisotropy coefficient greater than or equal to 5, anomalously large readings appear in the vicinity of the bed boundaries. These large readings are similar to the polarization horns that occur in dipping beds at high-contrast isotropic interfaces. In the case of a thin bed (e.g., < 5 ft) located between two massive shoulder beds, the large anomalies from the bed boundaries merge into a single anomaly at the center of the bed. This behavior was not expected and can be quantified only by modeling. Modeled results are also used to analyze the Schlumberger AIT Array Induction Imager instrument response in a crossbedded reservoir in the Nugget formation where we expect different values of R, and Rh.
Skip Nav Destination
March 01 2001
The Effect Of Crossbedding Anisotropy On Induction Tool Response
Petrophysics 42 (02).
Paper Number: SPWLA-2001-v42n2a6
March 01 2001
- Share Icon Share
- Search Site
Anderson, B.I., Barber, T.D., and S.C. Gianzero. "The Effect Of Crossbedding Anisotropy On Induction Tool Response." Petrophysics 42 (2001): No Pagination Specified.
Download citation file: