Extracting Continuous Profiles of Archie Parameters from Downhole Measurements

Abstract

AbstractArchie parameters, porosity exponent m and saturation exponent n, are required inputs for formation evaluation. Depending on rock types, both m and n are routinely obtained from core analyses, which require reservoir cores and fluids. Such determined m and n values are discrete data points and availability is often limited. The ultimate objective of this study is to investigate the possibility to establish a workflow to determine continuous profiles of Archie parameters m and n downhole from advanced logging measurements.The methodology was developed through laboratory studies. Carbonate and sandstone core samples were initially screened to have proper samples. Integration of NMR Diffusion D-T2 and dielectric permittivity was used to predict the m and n parameters, while resistivity was used as reference. The workflow consists of two steps: initially, m is derived from D-T2 NMR data using a model based on restricted diffusion, then the derived m is used to separate m from n in the dielectric derived MN parameter.Results firstly indicate that m derived from NMR correlates with the resistivity benchmarks for fully water saturated samples (Sw = 1). Secondly, the stability of the NMR derived m with the addition of oil in the pore space (Sw < 1) was demonstrated. When the samples were drained in steps (decreasing Sw) and workflow at each step was applied, the integrated NMR and dielectric measurements allowed to extract a n value in each step independently from the measurement in the other steps. The resistivity measurements at all the steps allowed to extract a single combined n used for benchmarking. Based on this study, the following are summarized:Archie m can be derived from NMR D-T2 data by using a process based on interpretation of restricted diffusion visible in the water signal of data acquired at Sw =1. The same can be applied to data acquired at partially saturated conditions by interpreting the water signal only. The m values derived from NMR measurements at partially saturated conditions can be combined with dielectric MN parameter to compute Archie n.