Evaluating the Variability of the Archie Cementation Factor m in Heterogeneous Carbonates: A Case Study from a Lower Cretaceous Reservoir in UAE

摘要

Carbonate reservoirs introduce challenge in providing accurate water saturation from conventional Archie equation. One of the reasons is due to the variability of the Archie cementation factor "m" because of complex and tortuous nature of these heterogeneous carbonates. The study was performed by integrating core and log data from advance measurements to understand the root cause and range of the variability and an attempt to link sedimentology and diagenetic facies to petrophysical groups. The Study focused on a carbonate reservoir with complex pore network. The formation resistivity factor (FRF) measurements were conducted with high-resolution sampling on a selected well. Each of FRF plug has associated porosity, permeability, thin sections, MICP, NMR and high-resolution dual energy micro CT scan. The m value from FRF is then plotted along the porosity-permeability plot. The capillary pressure parameters (entry pressure, slope, inflexion points) were extracted from MICP and relationship is plotted against m. Diagenetic facies described from the thin sections is compared versus m. Principal component analyses was conducted to identify factors relating to m. The uncertainty on water saturation associated to variable parameter m was assessed using Monte Carlo analysis on multiple wells. An advanced multi-frequency dielectric logging tool was run on couple of wells to provide variable water-phase tortuosity (MN) measurement. Specific analysis was performed to extract the variable m value from the measurement over limited zones, which has been derived from core "m" measurements. Several wells located on the flank of the reservoir below water level were evaluated. Dean stark measurements were performed on a well and used to validate the saturation calculation. It is obvious that the evaluated reservoir has high degree of heterogeneity as indicated by complex pore network with multi modal pore system as shown by the thin sections, MICP and plug CT Scan.