Research And Application Of Comprehensive Geophysical Technique In Deepwater Well Site Pre-drilling Risk Assessment

Marine geologic hazards happen based on a certain geographic landform and geological background. The reasons of all kinds of marine geologic hazards are com-plex and various. As the development of marine resources and the rapid development of ocean engineering construction, they are obviously affected by the marine geologi-cal hazards. In order to avoid the risk of marine geologic hazards, the corresponding geophysical survey is needed. The each investigation method has its own characteris-tics and solves different problems from different directions and by different means, but a single kind of method is often difficult to work alone. By pooling a large number of information data and making comprehensive analysis of geologic hazard formation conditions and characteristics from various angles, comprehensive geophysical me-thods can effectively improve the accuracy and effectiveness of geophysical informa-tion, reduce or avoid the adverse impact on offshore drilling caused by geological ha-zards.Firstly, the principles of multi-beam echo sounder, sub-bottom profiler, side scan sonar and 3D-Seismic shallow formation high resolution processing are dis-cussed and analyzed in the report. Secondly, the data of deep water oilfield(water depth 1000m-1300m) acquired in the south China sea is taken as an example to dif-ferentiate topographical feature of seabed on the basis of fine processing of data, identify the type of the geological hazards that may possibly affect the offshore drill-ing and analyze their characteristics and distribution. Base on the multi-beam bathy-metric data, make an analysis of water depth, topography and underwater gradient on the well site. By judging the side scan sonar image, differentiate seabed obstruction and amplitude anomaly areas, describe and assess different submarine geological ha-zards and their impact on engineering. By comparison and analysis of sub-bottom profile data, the sub-bottom strata of the well site is divided and interpreted according to the sedimentary features and strata reflections. Analyze the 3D seismic data ampli-tude,divide the amplitude anomaly zone and evaluate the submarine geological ha-zards of the research area.Results show that the main submarine geological hazards in the research area are seabed slopes, submarine landslides, seabed pocks, gas hydrate, mass transported de-posits(MTDs), etc. Seabed slopes, shallow gas, faults, MTDs and so on are directly affect the drilling activities in the proposed well location. Based on the comprehen-sive analysis of the interpreted results, the drilling favourability map is drawn in this report.The actual drilling results show that the conclusions in this paper are accuracy, and also indirectly prove that the method used in this paper is scientific. The compre-hensive geophysical method used in this paper, will provide reference for the future similar ocean development.