An integrated isotope-based fluid evolution and rock typing study, based on well cuttings and outcrop in Permian and Triassic successions of central and north east Thailand.

Abstract

An isotope-based (18O and 13C) study was used to describe how rock-fluid interaction is impacted by structural and diagenetic processes in a succession of Permian platform carbonate and
Triassic siliciclastics and volcanics in central and NE Thailand. Previously completed isotope studies have described fluid evolution resulting from structural and diagenetic processes within outcrops of Permian platform carbonates. This study is the first to extend this isotope-based
fluid evolution application from outcrop analog to the un-cored well bore. Permian platform carbonate outcrops and Triassic non-marine clastic outcrops were used as analogs for the subsurface, in a well that had penetrated a well-known Triassic volcanic formation, a shaley carbonate, and then an extremely hard unnamed “conglomerate” section. The mudlog interpretation for this well placed its base in a subthrust Permian sequence; however, analysis of the stable isotope spread in the lower part of this well indicates a C-O isotope plotfield that is not usually associated with subthrust Permian carbonates in Thailand. This study aimed to explain this anomaly and expanded the use of stable isotope analysis via determinations on selected well cutting samples and by examining the isotope signatures of shalier, as yet under-studied “off-platform’ Permian carbonates.