We present porosity and free gas estimates and their uncertainties at an active methane venting site in the UK sector of the North Sea. We performed a multi-disciplinary experiment at the Scanner Pockmark area in about 150 m water depth to investigate the physical properties of fluid flow structures within unconsolidated glaciomarine sediments. Here, we focus on the towed controlled source electromagnetic (CSEM) data analysis with constraints from seismic reflection and core logging data. Inferred background resistivity values vary between 0.6–1 $\Omega$m at the surface and 1.9–2.4 $\Omega$m at 150 mbsf. We calibrate Archie’s parameters with measurements on cores, and estimate porosities of about $50\pm 10\%$ at the seafloor decreasing to $25\pm 3\%$ at 150 mbsf which matches variations expected for mechanical compaction of clay rich sediments. High reflectivity in seismic reflection data is consistent with the existence of a gas pocket. A synthetic study of varying gas content in this gas pocket shows that at least $33\pm 8$% of free gas is required to cause a distinct CSEM data anomaly. Real data inversions with seismic constraints support the presence of up to $34\pm 14$% free gas in a 30–40 m thick gas pocket underneath the pockmark within the stratigraphic highs of a till layer above the glacial unconformity in the Aberdeen Ground Formation.

我们介绍了北海英国部分活跃的甲烷排放站点中的孔隙度和游离气估计值及其不确定性。我们在水深约150 m的Scanner Pockmark地区进行了多学科实验，以研究未固结的冰川海洋沉积物中流体流动结构的物理特性。在这里，我们集中在受地震反射和岩心测井数据约束的牵引式受控源电磁（CSEM）数据分析中。推断的背景电阻率值在0.6–1之间变化 $\Omega$m在表面和1.9–2.4 $\Omega$m在150 mbsf。我们通过岩心测量来校准阿奇参数，并估计孔隙率约为$50\pm 10％$ 在海底下降到 $25\pm 3％$150 mbsf，与富粘土沉积物的机械压实预期的变化相匹配。地震反射数据中的高反射率与气穴的存在是一致的。对这个气穴中各种气体含量的综合研究表明，至少$33\pm 8$需要使用％的游离气体才能导致明显的CSEM数据异常。具有地震约束的实际数据反演可支持多达$34\pm 14$在阿伯丁地面组冰川不整合面上方耕层的层状高点内，麻点下方30–40 m厚气穴中的游离气体百分比。