Field Trial of LWD NMR Tool for Accurate Estimation of Effective Porosity in Deviated HPHT Wells: A Viable Alternative to Wireline-Based NMR Tools

Abstract

The Tengiz reservoir is known for its substantial bitumen content, requiring careful differentiation during formation evaluation processes. To accurately estimate the effective porosity, wireline nuclear magnetic resonance (NMR) tools were used in conjunction with other logging tools. However, the increasing number of deviated wells drilled in Tengiz posed conveyance challenges for the wireline-based NMR tool due to high deviation angles. In light of this, TCO (Tengizchevroil) geoscientists sought opportunities to acquire NMR data using logging-while-drilling (LWD) technology in the reservoir section. Although the LWD NMR tool was not previously available for the required hole size, recent commercialization made it feasible. A team of geoscientists at TCO meticulously planned and executed a field trial of the LWD NMR tool to assess its potential future utilization in situations where the conveyance of wireline NMR tools may encounter difficulties. The LWD NMR tool was successfully deployed in a deviated well during drilling operations, followed by a subsequent measurement after drilling (MAD) pass to ensure log quality control. To verify and compare the acquired data, wireline-based NMR measurements were also conducted in the same well. The results of the field trial demonstrated the successful acquisition of high-quality LWD NMR data, corroborated by the MAD pass data and wireline log data. Furthermore, we revised and tested internal NMR data processing workflows, which conclusively established LWD NMR as a viable alternative to wireline-based NMR tools. Notably, the acquisition of NMR data while drilling offers additional benefits, as the near wellbore zone is not fully flushed with drilling mud, potentially enhancing fluid typing techniques (T1 and T2 distribution). This promising outcome opens up new avenues for more efficient and reliable estimation of effective porosity in deviated wells, as well as in wells with potential restrictions to run WL tools within the Tengiz reservoir and beyond, contributes to improved reservoir characterization and decision-making processes in asset development.