Anomalous features and controlling factors on the dynamic adjustment of marine gas hydrate system
Bottom simulating reflectors(BSRs)are crucial indicators of gas hydrate occurrences.Seismic profiles from oceans worldwide reveal diverse BSR types and depths,demonstrating the dynamic adjustment of gas hydrate systems on millennial timescales.This study compares and analyzes the seismic reflection characteristics and logging responses of different BSR types.Several key factors contribute to BSR shifts:① Fluctuations in sea level and seafloor temperature during glacial-interglacial cycles,coupled with rapid shallow sediment deposition,thrust folding,and basement uplift,can cause upward or downward BSR adjustments;② Thermal fluid release from late tectonic activity can drive BSRs upward shift;③Submarine erosion and formation overpressure can lead to BSR downward shift;④ Due to active heavy gas leakage from deep strata,structure Ⅱ hydrate readily forms.This results in the coexistence of hydrate and free gas at the base of the gas hydrate stability zone(BGHSZ)for methane;⑤ Double BSRs formed by mineral phase transitions are unrelated to gas hydrate in fine-grained sediments;⑥ Local thermal anomalies can cause the transition from gas hydrate to free gas layer within the same horizontal layer,showing a horizontal polarity reversal without BSR adjustment.Therefore,the dynamic adjustment of the BGHSZ reflects the continuous interplay of gas hydrate formation,decomposition,and reformation,which shows the three-phase coexistence of hydrate-free gas-water and the multiple shallow gas distributions.This results in various types of BSRs observed on seismic profiles,indicating the complexity of gas hydrate systems and their interplay with free gas.
gas hydratefree gasBSRthree-phase conexistencedynamic adjustment
万方数据
维普
