The Flow Zone Indicator (FZI) and Pore Geometry Structure (PGS) Rock Typing Comparison to Maximize Permeability Estimation on Carbonate Reservoir, Case Study: Kais Formation, Bintuni Basin

Abstract

Carbonate rock has high level of heterogeneity and it makes up the majority of reservoirs in the world, for example the Kais Formation reservoir. The heterogeneities of carbonate rock are influenced by mineral composition, diagenesis, and depositional environment. Those heterogeneities affect the permeability of the rock, so that it will produce a very high uncertainty in the formation evaluation process. The permeability value is one of the vital parameters in a reservoir, so it must be predicted with a high degree of accuracy. One of the ways is to characterize the reservoir using rock typing. Rock typing is performed in conventional coring data at1553 – 1738 feet MD), with 55 RCAL samples and capillary pressure (Pc). Rock typing begins by considering the geological features of the rock composition (lithology, colour, texture, mineral composition, diagenesis and depositional facies). Then the rock type Flow Zone Indicator (FZI) is obtained based on the calculation of the Rock Quality Index (RQI) and the normalization of the porosity value (ϕz), as well as rock type PGS which is used a comparison between pore structure and pore geometry. From those core analysis, there are with 6 rock types FZI, and with10 rock types PGS. The comparison of the predicted permeability values was carried out based on the equations from the rock typing results in each method. The permeability predictions using the FZI method showed a better level of relevance to the permeability values of the core data. In the un-cored well interval, cluster analysis was performed for rock typing which resulted in an undetailed rock type log as a calibration log for the Self Organizing Map (SOM) algorithm analysis, which produced a detailed rock type log, before re-doing the FZI analysis. The results of the estimated permeability (K) of FZI in the un-cored well intervals have correlation coefficient between 0.76 – 0.86 to the synthetic permeability log in the majority of available wells. New Rock Type (RT) for each well shows that RT-4 and RT-5 have fairly high value of flow units which indicates as good rock types in flowing fluids.