Hydrocarbon Distribution in the North Jakrawan Field, Pattani Basin, Gulf of Thailand

Abstract

Seismic data, wireline logs and geochemical analysis were integrated in an attempt to understand the petroleum system in the North Jakrawan field where gas pay distribution varies widely across the field. The objective was to investigate the factors that control hydrocarbon distribution across the field, in particular, why is there significantly more pay on one side of the field compared to the other. Structural maps of the MMU, C and K marker levels suggest that the North Jakrawan field is entirely influenced by north-south trending normal faults. East dipping synthetic faults conjugated by west dipping antithetic faults control the half graben geometry of the field. Isochron maps of sequence 3 (source rock and reservoir intervals) and 4 (reservoir intervals) also indicate that the formations thicken westward. Hydrocarbon generation windows suggest that gas-prone source rock (sequence 3) is currently mature on the eastern flank of the field while the western flank is overmature. Migrations are typically from west to east. The average net-to-gross calculated within each fault block indicates that there are more potential sand reservoirs toward the eastern flank. Clay smear calculation techniques confirm that sealing capacity of fault planes is typically effective. Analysis of the various components of the petroleum system in the study area suggests that hydrocarbon distribution is mostly controlled by migration effectiveness and structural closure. The western portion of the North Jakrawan field has a more effective petroleum system than the eastern portion, especially the downthrown block of fault A, where structural closure focuses hydrocarbon into an accumulation.