Sourceless Porosity and Anisotropy While Drilling Using Nuclear Magnetic Resonance and Azimuthal Acoustic LWD Tools Drilling Technology: A Case History

Abstract

A combination of nuclear magnetic resonance (NMR) and azimuthal acoustic tools was recently run in a logging-while-drilling (LWD) tool combination. This tool combination was used for the first time in Kuwait as a part of the bottomhole assembly (BHA), in addition to conventional tools, to acquire porosity without using radioactive sources. A deviated 8.5-in. borehole section of a well was planned through sand-shale sequences with a borehole inclination ranging from 0 to 90°. This geological section is typically crucial from a borehole stability point of view. Borehole deterioration and significant variations in pore pressure can create a high risk of becoming stuck-in-hole. The use of conventional porosity tools in a LWD BHA with installed radioactive sources would significantly elevate the risks to an environmental-hazard level. And, even retrievable based sources become problematic for successful extraction in high angle wells. LWD NMR and azimuthal acoustic tools, free of radioactive sources, were run for the first time in a LWD tool combination, with the primary objective to measure porosity, pressure prediction, and possible anisotropy using a centralized four-axis acoustic caliper. Previous experiences in the same geological setting encountered borehole enlargements by approximately 5 in. after only 15 to 16 hours. LWD helped bypass this issue and acquire high-quality data before borehole enlargement occurred. Additionally, indications of the presence of possible rock anisotropy were observed. The results were then correlated and matched to offset well data as well as with existing field geomechanics knowledge. This paper presents the planning, design, and execution of using LWD NMR and azimuthal acoustic tools in this well. It also discusses the viability, integrity, and robustness of logged data as well as interpreted results. Optimization of real-time drilling operations and petrophysical data acquisition requirements are also investigated to improve future field development and overall reservoir management strategies.