Towards a Robust Estimation of Permeability by Integrating Logging Data from Nuclear Magnetic Resonance, Acoustic, and Formation Tester

Abstract

Permeability is critical for determining the producibility of hydrocarbon reservoirs. Permeability, however, cannot be measured directly by logging tools, but rather needs to be deduced from available logging data. We present a method to derive a continuous permeability profile from nuclear magnetic resonance (NMR) and acoustic (AC) logging data by incorporating formation tester (FT) mobility. The underlying theory and workflow are described and field data examples that validate the approach are discussed. NMR permeability models combine porosity and an average pore size estimated from relaxation time measurements. Stoneley waves from acoustic logging deliver a permeability log by capturing the fluid particle motion between the borehole and the near borehole formation. Formation tester tools measure multiple formation properties including mobility, which is converted to permeability by multiplication with fluid viscosity. While NMR and AC data deliver a continuous, but uncalibrated permeability profile, FT mobilities are only taken at discrete depths with potentially large spacing. We have developed a robust workflow to generate a continuous and calibrated permeability log from NMR and acoustic data, by incorporating formation tester mobilities. The workflow can incorporate wireline and logging while drilling (LWD) data and can be applied to clastics and carbonate reservoirs. In particular, carbonates can exhibit complex pore geometries due to diagenetic alteration that can make permeability assessment difficult. Permeability in clastic formations, on the other hand, can be affected by the presence of clays or by cementation. We have observed that incorporating formation tester data can contribute significantly to deliver a calibrated, continuous permeability profile from NMR and Stoneley waves. We demonstrate the efficiency of our methodology by applying it to three field data examples from offshore carbonate formations. These examples demonstrate the value of integrating formation test mobility with NMR and, if available, acoustic permeability, to improve the petrophysical characterization of reservoirs. Advantages and limitations of the combination of all three measurement types are illustrated, and applications, such as the identification of pore geometry effects, are discussed.