Acoustic And Geochemical Evidences Of Shallow Gas Distribution Offshore Waropen Basin, Papua, Indonesia

Abstract

Sub-Bottom Profiling (SBP) records and results of geochemical analysis of 12 surficial sediment cores from various water depths collected from the offshore Waropen Basin-Papua are presented. Presence of gas is clearly observed on sub-bottom profiler records. Shallow gas was identified through acoustic response due to gas accumulation and gas escape on sub-bottom profiles. Acoustic evidences of gas accumulations within near surface geology consist of high amplitude reflections and associated acoustic blanking, gas plumes and morphological features like pockmarks. Total organic carbon analysis of 12 surface sediment cores varies between 0.5% to 1.3% which indicate that the sediments have an abundance of organic matters. Gas chromatographic analysis of hydrocarbon composition detected only methane, a biogenic origin of shallow gas. Acoustic and geochemical evidence in the Waropen Basin indicates extensive shallow gas accumulations in the Late Quaternary sediments, some trapped within these deposits and some escape from seabed into the water column which then created a high distribution of pockmarks.

The Occurrence of Recent-Subrecent Seabed Acoustic Anomalies and Its Relationship with Structural Uplift around the Waipoga Trough, West Papua-Indonesia

“…Geochemical data from Waipoga Trough reveals 0.5% to 1.3% of organic carbon concentration, which shows that the sediments have a fair to a good abundance of organic matter (Firdaus et al, 2021). Since the hydrocarbon composition identified on the sediment samples is only methane, it suggests that the origin of the shallow gas was biogenic methane origin.…”

“…The studied area (Figure 1) is situated in the eastern corner of Cendrawasih Bay, commonly called the Waipoga Trough (Firdaus et al, 2021). Three main geological structures border Cen- drawasih Bay, those are the Yapen-Sorong Fault Zone to the north, the Ransiki Fault to the west, and the Waipoga Fault to the southeast.…”

“…The pockmark feature on the seabed surface is a depression formed by local gas escaping into the surface (Hovland and Judd, 1988). Pockmarks are formed in fine-grained sediment layers due to the release of fluids or gases into the water column (Hovland and Judd, 1988;Firdaus et al, 2021). In acoustic profiles, pockmarks are expressed as minor depressions on the seabed surface.…”