南海神狐海域天然气水合物及气源条件海洋可控源电磁成像

A marine controlled-source electromagnetic imaging of gas hydrates and gas sources in the Shenhu area,South China Sea

地震剖面的似海底反射(BSR)指示了天然气水合物的底边界,并已得到钻探的验证。南海神狐海域是天然气水合物(简称水合物)研究的热点区域。然而,由于地质构造的复杂性且钻井数量有限,仅仅依靠地震与钻探研究不能完全描述区内天然气水合物及气源通道的分布。含水合物地层比围岩具有更高的电阻率,海洋可控源电磁(MCSEM)数据获得的电阻率能为水合物和气源通道检测提供重要依据。本文在神狐海域开展MCSEM探测研究,沿一条测线采集了15个站位的海洋可控源电磁场数据,通过数据处理与二维反演,实现了研究区海底二维电阻率成像。然后,通过灵敏度分析,检验了MCSEM反演结果的可靠性。结合SH-W07-2016随钻测井(LWD)和地震数据,对二维电阻率剖面进行解释,推断了剖面上水合物和游离气分布,划分了两种形式的水合物储层结构,分析了其构造成因。

The presence of a bottom simulating reflector(BSR)on seismic profiles serves as a reliable indicator of the lower boundary of natural gas hydrate accumulations,a phenomenon that has been confirmed by drilling data.The Shenhu area in the South China Sea is a prominent region for natural gas hydrate(referred to as“hydrates”)research.However,the complex geological structures andlimited spatial coverage of drilling sites pose significant challenges to comprehensively characterizing hydrate distribution and associated gas source channels through seismic and drilling data alone.The distinct electrical resistivity contrast between hydrate-bearing formations and surrounding rocks presents a unique opportunity for geophysical exploration.Marine controlled-source electromagnetic(MCSEM)data,which effectively captures this resistivity contrast,provides a valuable toolfor detecting both hydrates and gas source channels.This study presents the findings of MCSEM exploration research conducted in the Shenhu area.Electromagnetic field data were collected at 15 discrete sites along a designated survey line.Subsequent data processing and two-dimensional inversion yielded two-dimensional resistivity images of the seabed.The reliability of the MCSEM inversion results was rigorously evaluated through sensitivity analysis.By integrating logging-while-drilling(LWD)data from the SH-W07-2016 well and seismic data,the twodimensional resistivity profile was interpreted to infer the distribution of hydrates and free gas along the profile.Two distinct forms of hydrate reservoir structures were identified,and their structural origins were subsequently analyzed.