海底天然气渗漏系统演化特征及对形成水合物的影响

通过天然气沉淀水合物的动力学模拟计算,研究了墨西哥湾GC185区BushHill海底天然气渗漏系统的演化特征及对水合物沉淀的影响。渗漏早期,天然气渗漏速度大(q>18.4kg/m2-a),海底沉积以泥火山为主,渗漏天然气具有与气源天然气几乎一致的组成,形成的水合物具有最重的天然气成分。渗漏晚期,天然气渗漏速度很慢(q<0.55kg/m2-a),在海底附近没有水合物沉淀,主要以冷泉碳酸盐岩发育为主,水合物产于海底之下一定深度的沉积层中。介于二者间的渗漏中期(q:0.55～18.4kg/m2-a),海底发育水合物、自养生物群为特征,渗漏速度控制了水合物和渗漏天然气的组成及沉淀水合物的天然气比例。BushHill渗漏系统近10年的深潜重复采样显示,渗漏天然气和水合物天然气的化学组成在时空上是多变的,相对应的渗漏速度在时间上的变化约为3倍,在空间上的变化近2个数量级。

Evolution of Marine Gas Venting System and Impact on Gas Hydrate Crystallization

Based on the kinetic model of hydrate crystallization from venting gas in gas vent system, the evolvement characteristics and the impacts on gas hydrate crystallization in the Bush Hill gas vent system in GC 185 of Gulf of Mexico were studied. The venting rates are fast (gas flux q > 18.4 kg/m~-a) in the earlier stage of the gas vent system, mud volcano occurred on the seafloor, the vent gas has almost the same composition as the source gas, and the heaviest possible hydrates are crystallized near the surface. The venting rates are slow (gas flux q < 0.55 kg/m~-a) in the later stage, hydrate crystallization will not reach the sea floor, seep carbonate will be occurred on the seafloor. Between these extremes gas hydrate and seep community is developed on the seafloor of the gas vent system, and the vent and hydrate gas compositions, and the mass fraction of venting gas crystallized hydrate depend strongly on venting rate. Changes in vent and hydrate gas chemistry observed at multiple submersible visits to the Bush Hill vent system suggest the variations of venting rates between different submersible visiting time and different locations over the last 10 years.