Understanding Lateral Permeability Variations in Heterogeneous Carbonate Reservoirs Using Logging-While-Drilling NMR, Microresistivity Imaging, and Azimuthally Oriented Formation Testing

Permeability is a fundamental petrophysical attribute required to accurately evaluate recoverable reserves and design an appropriate field-development strategy. Because logging tools do not measure absolute permeability, minimizing uncertainty in the evaluation of log-derived permeabilities remains one of the most critical petrophysical challenges in the oil industry. Horizontal development in laterally heterogeneous carbonate reservoirs also requires evaluation of lateral permeability variations to optimize completion design while maximizing reservoir exposure via precise well placement in real time. This paper demonstrates innovative methods to evaluate lateral permeability variations in heterogeneous carbonate reservoirs. The workflow for log-derived permeability predictions is based on empirical relationships using nuclear magnetic resonance (NMR) and high-resolution imaging tool measurements. These are normalized in an integrated multidisciplinary approach using core, well test, production logs, and formation-tester mobility data where available. Traditionally, formation-tester tools have been used to obtain single-pressure and mobility values at each test station. The logging-while-drilling (LWD) formation tester can be oriented azimuthally to help evaluate permeability anisotropy, which is a key factor for reservoir characterization in laterally heterogeneous reservoir layers. The oriented data can also be used to adjust the well plan in real time to maximize reservoir exposure in the desired “sweet spot.” Variations in the oriented LWD formation-tester measurements at each depth station exhibited favorable correlations to azimuthal changes observed in the LWD high-resolution microresistivity image. Detailed image analysis further helped to understand the mechanism that governs the azimuthal permeability profile. The combination of oriented LWD formation-tester and high-resolution image data also aided in making better real-time geosteering decisions, as well as in the planning and design of a future field-development program within the local reservoir sector. Operational considerations to maximize data quality rely on an optimized bottomhole assembly (BHA) design, accurate depth control, and robust orientation techniques based on best practices and lessons learned. This paper presents an integrated approach for well placement and an improved understanding of flow-unit characterization via the first-time use of oriented formation-tester data in conjunction with corresponding high-resolution images in a laterally heterogeneous reservoir.