Methane hydrate systems off South Makassar Basin, Indonesia

Abstract Previous drilling and coring efforts have confirmed the presence of methane hydrates in the deepwater Makassar Strait of Indonesia. The strait, separated into the North Makassar Basin and South Makassar Basin, is situated on the thinned Eurasian continental crust that began to rift during the Middle Eocene. While past methane hydrates studies have focused on the northern basin, the southern region lacks equivalent investigation. This research employs legacy multi-channel seismic reflection and well logs data to decipher the methane hydrate systems and associated free methane in the South Makassar Basin. Identified through the interpretation of bottom simulating reflectors (BSRs), seafloor topography, and structural features on seismic reflection profiles are five primary play types: polygonal faults type, slope type, buried fold type, buried carbonate mound type, and sediment waves type. The distinctive characteristics of BSRs in this region can be summarized as follows: (1) predominantly located beneath topographic highs and basin depocenter, (2) typically displaying a series of high-amplitude dipping reflectors beneath BSRs, (3) the distribution of BSRs is not always continuous and is not always parallel to that of the seafloor, and (4) the presence of blanking reflection above BSRs is variable. These features suggest methane hydrate accumulation preferentially occurs beneath structural highs and in basin depocenters, likely due to the upward and lateral migration of buoyant, methane-rich fluids. Through the analysis of seismic amplitude distribution and reflection strength in relation to BSR depth, hydrocarbon distribution is categorized into methane-hydrate reservoirs above BSRs and free methane reservoirs below BSRs. A first-order estimation of methane resources via petrophysical approach and Monte Carlo simulation suggests approximately 105 trillion cubic feet (TCF) of methane resources.