莺歌海盆地底辟带DF区天然气地球化学特征差异及其成因

摘要

Natural gas geochemistry, fluid inclusion analysis and gas reservoir accumulation tracers, have been used to study natural gas geochemical characteristics, genetic types, filling period, cause of carbon⁃isotope partial inverse sequence and the causes of gas variability both vertically and horizontally in the high⁃temperature and high⁃pressure belt in the central diapiric zone of the Yinggehai Basin. In the high⁃temperature and overpres⁃sure area, natural gas is thermogenic coal⁃type gas, and the partial inversion of carbon isotopes of alkane gas is caused by the mixture of multi⁃period gases that are of different maturities. There are four periods of fluid filling in the high⁃temperature and overpressure area. The first two periods are mature or high⁃maturity alkane gas, while the second two periods are high⁃maturity or over⁃mature alkane gas and inorganic CO2.The filling period of the high⁃maturity and over⁃mature alkane gas is earlier than that of the inorganic CO2 . The influence of different diapiric activity, together with different gas migration channel types and development is the main reason for gas differences in different high⁃temperature and high⁃pressure zones. Multi⁃periodic diapir activity and periodic occurrence of overpressure caused the gas chemistry differences inside and outside of the high⁃temperature and high⁃pressure zone in the diapir core of D1⁃1 and nearby D13⁃1.%以现代天然气地质学理论为指导，综合运用天然气地球化学分析技术、流体包裹体技术及油气成藏储层示踪技术，对莺歌海盆地中央底辟区中深层高温高压带天然气地球化学特征、成因类型、充注期次、碳同位素序列局部倒转的成因及纵横向天然气地球化学特征差异形成原因进行了研究。结果表明：高温超压带内天然气皆为热成因煤型气，其烷烃气碳同位素系列局部倒转是多期次不同成熟度天然气混合所致；高温超压带内存在4期流体充注，前2期为成熟—高成熟烷烃气，后2期为高—过成熟烷烃气和无机成因CO2，且高—过成熟天然气充注期早于无机成因CO2；底辟活动影响强度差异及天然气运移通道类型和发育方式不同，是形成不同地区高温高压带天然气地球化学特征差异的主要原因，底辟多期活动和超压带周期性愈合导致D1－1底辟核部区及其周缘D13－1区高温高压带内、外天然气地球化学特征差异。