南海北部神狐海域输导体系特征及其对天然气水合物成藏的影响

基于地震解释和二维盆地模拟,从输导体系的类型、断层的活动性、古压力演化历史等方面综合研究南海北部神狐海域输导体系的特征,并结合生烃条件和天然气水合物稳定域条件,综合探讨输导体系对天然气水合物成藏的影响,进而预测神狐海域天然气水合物有利聚集区。结果表明：神狐海域输导体系类型主要有＂断层＂型和＂气烟囱＂型2种,并以＂断层＂型为主;＂断层＂型输导体系主要分布在神狐海域北部和中东部,断层性质为正断层,组合样式包括鹿角状、反＂y＂字型和阶梯型,断层主要活动期为珠江期—韩江期;该区域经历了3期超压旋回,其中第3次超压旋回与深部烃类流体的生成排放有关;该区域浅层形成了较厚的天然气水合物稳定域,深部具备充足的气源;该区域主要生排烃期与断层主要活动期、第3次超压旋回匹配良好,有利于深部烃类气体通过＂断层＂型输导体系向浅层运移;该区域北部和中东部是未来天然气水合物勘探的有利区。

Characteristics of Passway Systems and Their Influence on Gas Hydrate Accumulation in Shenhu Area of Northern South China Sea

Based on seismic passway system, activity of interpretation and 2D basin simulation, according to the types of fault and evolution history of paleopressure, the characteristics of passway system in Shenhu area of northern South China Sea were comprehensively studied; combined with hydrocarbon generation condition and stability region condition of gas hydrate, the influence of passway system on gas hydrate accumulation was discussed, and then the favorable accumulation area of gas hydrate in Shenhu area was predicted. The results show that the types of passway system in Shenhu area are ＂fault＂ and ＂gas chimney＂, and the former is prevailing; passway systems with ＂fault＂ type are mainly distributed in the north and middle-east of Shenhu area, and faults, which are active mainly in Zhujiang-Hanjiang period, are normal with the combined styles of staghorn, reverse ＂y＂ and step; there are three overpressure cycles in Shenhu area, and the third overpressure cycle is related to the generation-expulsion of deep hydrocarbon fluid; thick gas hydrate stability region is formed in shallow layer and gas source is sufficient in deep layer of Shenhu area; the main hydrocarbon and expulsion stages, which match well with activity of fault and the third phase of overpressure cycle in Shenhu area, is favorable for the migration of hydrocarbon gas from deep layer to shallow layer through passway systems with ＂fault＂ type; the north and middle-eastern regions of Shenhu area are favorable for gas hydrate accumulation.