Quantification and Correction of Lateral Motion Effects on NMR Logging While Drilling

Abstract

Monitoring downhole drilling dynamics is an essential element to quality check the measurements provided in logging while drilling (LWD). LWD nuclear magnetic resonance (NMR) is sensitive to the motion induced from the bottom-hole assembly (BHA) during drilling, therefore, quantifying the motion effects becomes important to understand how to correct the measurements. Quantification and correction of lateral motion effects on NMR LWD are the objectives of this paper. Data was collected from various BHA combinations with LWD NMR to model the responses, which were compared with actual downhole conditions to assess the need for the lateral motion correction (LMC). Vibrational assessment criteria are utilized to assign a severity level, which dictates the level of the LMC. The LMC applies an algorithm to differentiate true formation signal responses from the vibration signal response. Specifically, the motion effect function was integrated into the forward matrix of the NMR joint inversion, and a nonlinear optimization algorithm was used to determine the four motion parameters, and if present, compensate for lateral motion effects. In wellbores with severe motion vibration there were large discrepancies between real-time and memory data, which resulted in mismatches with the measured partial porosities. Investigations were conducted on the BHA design, well trajectories, and wellbore environment to quantify the lateral motion effect on the NMR measurement. This information was then compiled to incorporate all aspects of BHA design techniques to mitigate the lateral motion effects on the NMR measurement. The LMC algorithm gives added confidence to ensure all data collected is consistent and reliable even in more challenging wellbore environments, which could be subjected to unanticipated lateral motion. This paper highlights an approach to integrate BHA simulation principles to anticipate severe motion effects during drilling. This knowledge, coupled with the LMC, creates a platform to enhance NMR data quality.