Polarization Horn as Key in Identifying Resistivity Contrast at High Angle: An Observation from Six Successful Horizontal Wells, Natuna Sea Block B

Abstract

Abstract Horizontal wells are judged to be the best alternative for depleting reserves efficiently and recovering optimum reserves from certain Conoco fields in Block B. From mid 2000 to early 2001, Conoco successfully drilled 3 horizontal gas wells and 3 horizontal oil wells. These wells achieved initial test flow rates ranging between 59 to 64 MMCFGPD in the gas wells and between 6,500 to 8,000 BOPD in the oil wells. These successful results were achieved by careful prewell design, incorporating 3D seismic and adjacent well data to better predict structural features and the petrophysical model of the planned well path. However, the subsurface remains uncertain. To help predict the landing point in the reservoir target, a polarization horn phenomenon is utilized. This phenomenon is an artifact of propagation resistivity tools, when approaching bed boundaries having great resistivity contrast, at high angle. Monitoring this effect while drilling is important because it can help determine whether a well should continue into its planned horizontal path, or needs to be side-tracked to an alternate location. This polarization horn phenomenon and prediction of permeability using measured resistivity are the key tools used for geo-steering the successful horizontal wells.