Skip to Main Content
Logging-while-drilling (LWD) borehole sensors are used to provide real-time resistivity data of adjacent earth formations for hydrocarbon exploration. This allows for a proactive adjustment of the dipping angle and azimuth direction of the drill and, hence, geosteering capabilities. The analysis of borehole eccentricity effects on LWD sensor response in full 3 3 anisotropic earth formations is important for correct data interpretation in deviated or horizontal wells. In this paper, we present a cylindrical-grid finite-difference time-domain model to tackle this problem. The grid is aligned to the sensor axis to avoid staircasing error in the sensor geometry but, in general, misaligned to the (eccentered) borehole/formation interface. A locally conformal discretization is used to compute effective conductivity tensors of partially-filled grid cells at those interfaces, involving an isotropic medium (borehole) and a full 3 3 anisotropic medium in general (dipped earth formation). The numerical model is used to compute the response of eccentered LWD sensors in layered earth formations with anisotropic dipping beds.
Geoscience and Remote Sensing, IEEE Transactions on (Volume:50 , Issue: 3 )
Date of Publication: March 2012