Field examples of the joint petrophysical inversion of resistivity and nuclear measurements acquired in high-angle and horizontal wells

Abstract

A recently introduced interpretation workflow has confirmed that inversion-based interpretation is more reliable than conventional well-log analysis in high-angle (HA) and horizontal (HZ) wells because the former accounts for well trajectory and shoulder-bed effects on well logs. Synthetic examples show that the inversion workflow could improve the estimation of hydrocarbon volumes by 15% and 10% in HA and HZ intervals, respectively. Using field examples of thinly interbedded calcite-cemented siltstone formations, we document results of the joint petrophysical inversion of logging-while-drilling multisector nuclear (neutron porosity, density, natural gamma ray, photoelectric factor) and multiarray propagation resistivity measurement for improved formation evaluation in HA/HZ wells. Under the assumption of multilayer formation petrophysical models, the inversion approach estimates formation properties by numerically reproducing the available measurements. Subsequently, inversion-derived hydrocarbon pore volume is calculated for assessment of reservoir pay. Application of the joint inversion-based interpretation in challenging field examples highlights petrophysical characteristics such as capillary trends or water saturation variations in a hydrocarbon column influenced by reservoir quality and formation electrical anisotropy which otherwise remain inconspicuous with conventional and quick-look interpretation of well-logs.