Correcting LWD Propagation Resistivity Logs in Horizontal Sinusoidal Wells for Better Water Saturation Estimate: Case Study in a Deepwater, Channelized Turbidite Reservoir

Abstract

Abstract Today's advanced drilling and geosteering technologies have enabled high-angle horizontal (HAHZ) wells to become common and routine. However, quantitative petrophysical analysis in such an environment is still lagging behind, mainly because of the complexities of the tool response, the lack of fast modeling capabilities and fit-for-purpose softwares. In deepwater channelized turbidite reservoirs, where lateral heterogeneities can be great, a strategy for reducing horizontal well placement risk is the use of sinusoidal pilots. The high deviation angle between the logging while drilling (LWD) tool axis and the formation bedding introduces uncertainty and inaccuracy in the resistivity measurements. These can make petrophysical analysis in HAHZ wells difficult, especially when there are no offset vertical wells available. It is thus necessary that these well deviation effects be corrected before a petrophysical analysis is conducted. In this paper, we first review the tool response characteristics of LWD resistivity logs in HAHZ wells. Then we present a practical workflow to correct for the well deviation effects on LWD resistivity logs through an efficient, highly interactive software, illustrated by both a synthetic data set and several real world examples. It is shown that using this workflow, which can be defined as an interactive inversion, the raw resistivity logs can be significantly corrected to values closer to the true formation resistivity (Rt). The use of Rt instead of the LWD resistivity logs for calculating water saturation (Sw) yields more accurate Sw numbers, which in turn reflect in more accurate reserves estimation. The main challenge is there are still about 30% of logs in the study area are beyond the repair. The development of new hardware with more information content is deserved to address the issue.