Fracture Characterization in Contrasting Platform Carbonate Facies, Muak Lek and Chumphae Area, Central – Northeast Thailand

Abstract

A fracture characterization of Saraburi Limestone outcrops in Muak Lek and Chumphae quarries is conducted to develop a facies-based understanding of fracture distribution in exposed Permian limestones of Thailand. This is the first stage in developing an analogue understanding for fracture distributions in subsurface limestone reservoirs of Thailand and elsewhere. In the Muak Lek area, fracture density shows strong relationship with the host rock; the fine-grained lithofacies, with their thinner beds and smaller elastic moduli, show higher fracture densities and smaller apertures compared to the adjacent coarser-grained lithofacies. In contrast to Muak Lek, the Chumphae outcrop, because of apervasive diagenetic-silica cement overprint, has similar fracture densities across the various lithofacies. In summary, in outcrop analogs to fractured Permian carbonates that constitute potential reservoirs in the subsurface of central and northeastern Thailand, the fracture density and fracture aperture are responses to variations in the mechanical strength. In some diagenetic situations these relationships are resolvable in a gamma log, in others they are not. This has significant implications when a gamma log is used to cluster FMI-based fracture observations in wells in subsurface platform carbonates.