ABSTRACT

The Logging While Drilling (LWD) acoustics field has seen significant development, with applications in both open and cased holes. This case study delves into the critical aspect of ensuring the quality of LWD acoustic data across various applications, including real-time Top of Cement (TOC) evaluation and a novel approach to enhancing the reliability of shear wave slowness measurements.

In the deepwater Gulf of Mexico, operators in the Oil and Gas (O&G) sector face a stringent requirement for TOC evaluation before advancing to the subsequent drilling phase. The conventional wireline (WL) cement evaluation necessitates a separate run, incurring additional rig time and costs. The real-time TOC detection achieved through LWD monopole data demonstrates good agreement with post-processing and other WL cement bond measurements. This synergy not only streamlines the operation but also eliminates the need for a separate run for WL logging, providing significant time and cost savings for our clients.

For the LWD environment, quadrupole mode is the standard for assessing shear in slow formations. The old centroid-phase-slowness based dispersion correction method is prone to high uncertainty, particularly in faster formations. Often, it leads to gaps in shear data delivery. The introduction of Slowness-Frequency-Coherence (SFC)-based parameterized inversion technique offers a more robust and comprehensive assessment of shear properties across varying formations. It agrees with refracted shear, where applicable. To enhance data quality control, the novel inverted method presents the phase slowness discrepancies between field data and modeling phase slowness at each level.

INTRODUCTION

Over the past two decades, logging while drilling (LWD) acoustics has gained significant traction among oil companies as a valuable tool. Its real-time data acquisition capabilities empower geoscientists and engineers to make informed decisions during drilling operations. LWD acoustic measurements offer insights into formation properties like mechanical strength, porosity, lithology, and fractures. Additionally, they play a crucial role in evaluating cement placement and bond quality in cased holes (Pistre et al., 2014, Wang et al., 2019, and Bicalho et al., 2020), essential for ensuring well integrity, isolation, and completion.

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