Subsurface plumbing system architecture in the South Makassar Basin, offshore Indonesia, and its implications for methane emissions and geological storage

TL;DR

This study explores fluid flow systems in the South Makassar Basin and their impact on methane emissions and CO₂ storage potential.

Contribution

The study provides a new four-stage model for focused fluid flow and seal bypass development in deep-marine basins.

Findings

Focused fluid flow is expressed through fluid pipes and pockmarks rooted at carbonate structural highs.

Unfocused fluid flow is indicated by polygonal and radial fault networks coinciding with gas hydrate occurrences.

A four-stage evolutionary model explains seal bypass development influenced by pressure and mechanical heterogeneity.

Abstract

Subsurface plumbing systems in deep-marine basins influence gas hydrate distribution, natural methane emissions, and seal integrity relevant to subsurface CO₂ storage. Using high-quality, post-stack time-migrated (PSTM) 3D seismic reflection and well data from the South Makassar Basin, offshore Indonesia, we characterised both focused and unfocused fluid-flow features within a fine-grained seal succession that form endmembers of a fluid-flow continuum. A focused system is expressed by fluid pipes rooted at carbonate structural highs and, in many cases, terminating at the seabed as pockmarks. An unfocused system is expressed by laterally extensive polygonal and radial fault networks that spatially coincide with laterally continuous bottom-simulating reflections (BSRs), indicating gas hydrate occurrence. Based on mainly seismic reflection data, we propose a four-stage evolutionary model for focused flow, from radial faulting centred at structural highs, followed by pipe formation, and eventual seal breaching expressed as pockmarks on the seabed. These stages define a structurally mediated continuum of seal bypass development that is probably modulated by reservoir pressure buildup, reservoir geometry, and mechanical heterogeneity of the overburden. These findings provide new insights into the architecture of subsurface plumbing systems in the South Makassar Basin and has implications for natural methane seepage and long-term subsurface storage there and elsewhere.

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