FACIES DISTRIBUTION AND DIAGENETIC EVOLUTION OF A CARBONATE RESERVOIR IN PHA NOK KHAO FORMATION, SINPHUHORM, THAILAND

Abstract

Structure likely controls the reservoir quality in the Sinphuhorm field, NE Thailand as is indicated by rapid lateral changes in reservoir quality between closely spaced exploration and delineation wells in this field. Fluids that entered the subsurface system are associated with different stages of deposition and diagenesis. Variations in oxygen isotope values are indicators of the fluid temperatures in different events. A field study in Permian carbonates in quarries in CentralThailand has documented the isotope signature of various fluid events that can be used as a template to classify the diagenetic evolution of these carbonates (Warren. et. al, 2011).

This research focuses on subsurface data from well cuttings in PhuHorm field and generates a carbon-oxygen isotope set of plotfields that are integrated with petrophysical data, core analyses and related information. Drill cuttings from 3 wells are selected for isotopic analysis and classified by lithology into 6 groups to differentiate diagenetic events in each of the wells.The isotopic results in a δO18PDB and δC13 PDB crossplot define 2 trends of diagenetic significance in Pha Nok Khao Formation. The main compaction burial trend in the study area is consistent with the typical Indochina burial trend, showing samples from this trend are not related to high temperature fluid crossflows that indicate veins in thrust-fault damage zones. Trend 2 was not recognized in the outcrop studied by Warren et al. (2014). It is defined by a slight increase in oxygen isotope value and decrease in carbon isotope value likely related to cooling and uplift tied to a later possibly Paleocene event. It is recommended that a core-based study is undertaken on existing core in Phu Horm field to test the isotope work on cuttings and to prove that trend 2 is related to a deep meteoric circulation event.