可燃冰与油气双储层模型的海洋可控源电磁响应特征模拟分析

Characteristics of simulated marine controlled-source electromagnetic responses of coupled gas hydrate and petroleum reservoir models

利用海洋可控源电磁(MCSEM)法可识别海底电阻率异常体,在海洋油气探测中得到了广泛的应用。基于复杂电性结构海底地层模型,提出一种基于预条件迭代求解的频率域矢量有限元电磁正演模拟方法,基于不完全LU分解的预条件方法,提高了迭代求解效率,层状模型模拟结果验证了方法的有效性。基于结构化任意六面体单元建立了真实的南海某海域地电模型,并针对不同构造矿藏储层特征,分别建立了深埋藏油气储层模型、可燃冰矿体模型及复杂基底地质模型,得到了不同激发、接收模式下的MCSEM响应特征:收发距较小时,地形影响较明显;对于埋藏较浅的可燃冰矿体,收发距较小时异常明显,而埋藏较深的油气储层则在收发距较大时异常明显。

Marine controlled-source electromagnetic method(MCSEM)can be employed to identify resistivity anomalies on the seafloor and is thus widely used in offshore petroleum exploration.A simulation method of frequency-domain vector finiteelement electromagnetic forward modeling based on preconditioned iterative solution is proposed on the basis of a complex seafloor strata model with a complex electrical structure.The preconditioning method based on incomplete lower-upper(ILU)decomposition improves the efficiency of iterative solution.The simulation results of the layered model verify the effectiveness of the method.A geoelectric model of a certain area of the South China Sea is built with arbitrary hexahedral structured elements.A deep-buried petroleum reservoir model,a gas hydrate deposit model,and a geological model with a complex basement are built,respectively,according to the reservoir characteristics of deposits with different structures.The characteristics of MCSEM response are analyzed under different excitation-receiving modes.Specifically,when the offset is small,the influence of topography is obvious.The influence is especially salient on shallow-buried gas hydrate deposits when the offset is small,while it is more distinct on deep-buried petroleum reservoirs when the offset is large.