Lithofacies classification based on open hole logging using ternary diagram techniques

Abstract

The composition of the sandstone reservoir in Malay Basin sequences is dominated by sand size fraction followed by silt and clay sizes, respectively. Depositional environments in these types of sediments controlling the sand, silt, and clay fraction distribution where the proximal part of the delta characterized by more sand than silt and clay due to high energy, however, the distal part tend to have fines from silt and clay rather than sand fractions. To date the facies and lithofacies identification and classified based on the description of core analysis, which is always limited due to cost of the core samples. To minimize the uncertainty due to minimum core, the current approach was used to help the geoscientist to identify the lithofacies classification based on ternary diagram. The proposed approach is to use the ternary diagram to identify and classify the lithofacies based on the clay, silt, and sand volume produced from well logging interpretation including traditional logs and NMR technology. The fractions of the sand, silt and clay can be calculated from openhole logging based on gamma ray, density and neutron logs using the PETRONAS algorithm SSC model to compute the volume of the three fractions (sand, silt, and clay). The volume was calibrated with XRD data and sieve analysis. Ternary diagram was used to identify the lithofacies association for the reservoir interval which showing a good match with rock typing identified from porosity/permeability of core data. NMR technology used to derive grain-size-distributions in contrast to core analysis, NMR provides a continuous along hole profile of grain-size-distributions which have match with LPSA and sieve analysis, which can be utilize a continuous grain-size-distribution profile. Based on the T2 cutoff we can easily define clay, silt and sand volumes. The study was conducted blindfolded, without initial reference to core studies, to test the robustness of the methodology. Ternary diagram considered as a good tool for lithofacies association in the interval where no core date. The defined sand, silt, and clay volumes normalized to 100% were used to compute the actual volume of each then input into the ternary diagram to identify the lithofacies association. The proposed model will help to minimize the uncertainty as a fit-for-purpose approach by improving the lithofacies association which can be translated to rock typing to improve the facies distribution in the static model and consequently, reserve estimations.