Distribution of shallow gas at an offshore platform site in Bohai Bay and its genetic mechanism

Submarine shallow gas has a serious impact on the structural stability of seafloor strata, so it has become an important factor affecting the safety of offshore platforms.Based on high-precision shallow stratigraphic profiles and single channel seismic data, the distribution and top buried depth of shallow gas around an offshore platform in Bohai Bay were identified, and the origin of shallow gas in the study area was analyzed.The distribution of shallow gas interpreted by shallow strata and single channel seismic data is very consistent with the top buried depth.The shallow gas in the area of 1 km² around the platform is mainly distributed in its north side and adjacent to its southwest corner in the form of patches or strips and locally in the form of points.The burial depth of top boundary is between 0.6 m and 4.0m.The shallow gas in the study area is shallow biogenic gas, but the fault development in this area does not rule out the existence of pyrolytic shallow gas.The influence of shallow gas on offshore platform is mainly manifested in two aspects of deformation and instability.This conclusion has practical significance for taking targeted protective measures for offshore platform.