Study on the Mechanism of Natural Gas Hydrate Decomposition and Seabed Seepage Triggered by Mass Transport Deposits

Abstract

Previous studies indicate that mass transport deposits are related to the dynamic accumulation of natural gas hydrates and gas leakage. This research aims to elucidate the causal mechanism of seabed seepage in the western region of the southeastern Qiongdongnan Basin through the application of seismic interpretation and attribute fusion techniques. The mass transport deposits, bottom simulating reflector, submarine mounds, and other phenomena were identified through seismic interpretation techniques. Faults and fractures were identified by utilizing variance attribute analysis. Gas chimneys were identified using instantaneous frequency attribute analysis. Free gas and paleo-seepage points were identified using sweetness attributes, enabling the analysis of fluid seepage pathways and the establishment of a seepage evolution model. Research has shown that in areas where the mass transport deposits develop thicker layers, there is a greater uplift of the bottom boundary of the gas hydrate stability zone, which can significantly alter the seafloor topography. Conversely, the opposite is true. The research indicates that the upward migration of the gas hydrate stability zone, induced by the mass transport deposits in the study area, can result in the rapid decomposition of gas hydrates. The gas generated from the decomposition of gas hydrates is identified as the principal factor responsible for inducing seabed seepage. Moderate- and low-speed natural gas seepage can create spiny seamounts and domed seamounts, respectively.

A Review on Submarine Geological Risks and Secondary Disaster Issues during Natural Gas Hydrate Depressurization Production

“…The second production test, at Nankai Trough in Japan, utilized a series of sand control measures to limit sand production. Production tests in 2017 and 2020 in the Shenhu Sea area did not experience wellbore plugging caused by sand outflow due to sand control measures [40][41][42][43]. The entry of sand into the production well and pipeline can cause equipment to wear out, reducing its useful life and increasing maintenance and replacement costs.…”

“…When sand production reaches a critical point, it can cause the formation of numerous holes and lead to continuous collapse. This can result in submarine subsidence and trigger engineering geological disasters, such as natural gas leakage or eruptions [41]. Hydrate reservoir collapse caused by Sand production is one of the key submarine geologic risks limiting the long-term and effective development of gas hydrate resources, and the behavior of sand production has attracted attention since the first marine hydrate development test in Japan was prematurely terminated in 2013 due to wellbore clogging problems caused by sand production.…”

“…When sand production reaches a critical point, it can cause the formation of numerous holes and lead to continuous collapse. This can result in submarine subsidence and trigger engineering geological disasters, such as natural gas leakage or eruptions [41]. Hydrate reservoir collapse caused by sand production will easily destabilize overburden.…”

“…4.5 m (horizontal well) 2.3 m (vertical well) Rutqvist et al [72]Eastern Nankai Trough, Japan 6 days Depressurization through a vertical well 15 cm Uchida et al[41] …”