Geological Characteristics of Mud Volcanoes and Diapirs in the Northern Continental Margin of the South China Sea: Implications for the Mechanisms Controlling the Genesis of Fluid Leakage Structures

Abstract

Mud volcanoes and diapirs are geological structures formed due to arch piercing or diapiric intrusion of ductile sedimentary materials into the overlying strata along high permeability channels. A detailed study on the processes controlling the formation of mud volcanoes and diapirs in the northern continental margin of the South China Sea is of vital importance to the exploration of economically viable oil and gas reservoirs and can be helpful to the exploration of natural gas hydrate in a sedimentary basin. The fluid seepage structures that occur in the Mesozoic and Cenozoic sedimentary basins of the northern South China Sea show significant differences in their morphological and tectono-structural characteristics. We used high-resolution seismic profiles and instantaneous frequency profiles to understand the mechanisms that are critical with respect to the differential development of the investigated piercement structures. Differences in stress field do not directly lead to the difference in the scale of mud volcanoes or diapirs. Fractures may play an important role in the formation of mud volcanoes and diapirs. The thickness of the sediment was found to have a strong impact on the formation of fluid leakage structures that thicker sediments are more conducive to the development of mud diapirs and the thinner one is more likely to form mud volcanoes.

Gravity Data Allow to Image the Shallow‐Medium Subsurface Below Mud Volcanoes

“…The gas leaked into the FAA probably in association with over-pressured mud dykes (Tingay et al, 2009) and/or directly into the fractured porosity of the fault damage zone. Similar situations of mud diapirism and intrusion along fault zones have been described also by Bonini ( 2020 Wang et al (2022), andZhong et al (2021). The gravity data that we present, however, are not in agreement with the seismic line interpretation presented in Maestrelli et al (2019) who at 0.5-0.6 s depth still interpret the reflectors in the sequence as belonging to the FAA; we believe that those reflectors are within the Miocene sequence where there is enough significant contrast in acoustic impedance.…”

“…(2022), and Zhong et al. (2021). The gravity data that we present, however, are not in agreement with the seismic line interpretation presented in Maestrelli et al.…”

Future challenges on focused fluid migration in sedimentary basins: Insight from field data, laboratory experiments and numerical simulations

“…These structures are produced by arching or diapiric intrusion into the overlying sediments along high permeability channels, such as zones of mechanical weakness, like fractures and faults [113,114]. However, such structures are more related to mud diapirs and mud volcanoes as they are piercement structures formed by high subterranean pressure imposed on ductile material in deep basins hosting relatively thick sedimentary sequences [115]. As shown in fossil analogues, they do not represent fluid pipes.…”

Shallow Strata Expressions of Leakage and Seepage Structures Associated With Hydrocarbon Migration: a Seismic Analysis on Offshore Barreirinhas Basin, Brazilian Equatorial Margin

“…The cold seeps are direct hydrocarbon indicators (DHI), which play a crucial role in the exploration and extraction of oil-and gas-bearing elds (Serié et al, 2012;Zhang et al, 2018;Goulart et al, 2019;Ma et al, 2021;Zhong et al, 2021). For instance, Cronin et al (2022) identi ed pockmark trains within submarine canyons and channels of the giant Jubilee oil eld, Tano Basin (Ghana).…”

“…Sea oor mounds include mud volcanoes, gas hydrate mounds, and carbonate buildups of deepwater settings (Dimitrov, 2002;Hovland and Svensen, 2006;Zhang et al, 2021). These mounds present a common association with bottom simulating re ectors (BSR) and hydrocarbon-related diagenetic zones (HRDZ) (Hovland and Judd, 1992;Zhong et al, 2021). BSRs represent the boundary between solid hydrate found within the gas hydrate stability zone (GHSZ), and the free gas zone (Satyavani et al, 2005;Roberts et al, 2006).…”