| Ocean Bottom Dual-sensor(OBD)acquisition technique is widely used in Oil and Gas industry for several reasons,such as adaptability to acquire seismic data in obstacle area,wide operational time window,realization of wide azimuthally acquisition,and elimination of ghosts and reverberations of the water layer as well as the convenience in conducting 4D seismic.Geophone and hydrophone of OBD are deployed together at sea bottom to conduct seismic data acquisition.Response differences between geophone and hydrophone,typical marine geometry,changing operational environment,like tides,bathymetry and sea bottom topography,are bound to affect the data quality of OBD acquisition.Thus,in OBD data processing,special techniques are needed to address the inherent characteristics of OBD data.In this dissertation,factors which impact on the OBD data quality and their corresponding correction methods were studied.The scopes of the study covered from the influences of response differences between hydrophone and geophone and operational environment variations,e.g.tides,sea water velocity changes,seabed topography and water depth,to their respective correction methods.OBD data summation technique and migration method were also dealt with in this dissertation.First,the influences of response differences between hydrophone and geophone and their correction method were discussed.The differences in amplitude and phase responses of geophone and hydrophone and detector-seabed coupling were studied on a basis of mechanics principle in vibration system.Corresponding correction methods were also put forward.With these methods,the energy,frequency and phase consistency between geophone and hydrophone data had been improved and high signal to noise ratio datasets had been achieved.These laid a solid foundation for the following data summation and migration processing.Second,Theoretical analysis of their impacts of sea condition,sea water velocity changes,seabed topography and water depth on seismic data were carried out and their correction methods were proposed.The water layer correction method based on statistical characteristics of dataset improved the accuracy and practicality,compared to the traditional tidal correction and sea water velocity changing correction.The influences of seabed topography and water depth on OBD data were eliminated with wave-equation datuming which was beneficial for velocity analysis and normal moveout and statics corrections.For OBD data summation,firstly,the response characteristics of hydrophone and geophone to water layer reverberations were analyzed based on wave theory and the physical natures of how the OBD seismic data to suppress water layer reverberation were given.Next,reasonableness of this theory was verified and the process of suppressing water layer reverberations was illustrated with convolution model data.Finally,the shortcomings of traditional summation method were analyzed and a summation method based on real ray-path in tau-p domain was put forward.Summation results of the synthetic and field datasets have been improved greatly with the tau-p domain ray-path based summation method,which showed this method is effective and practical.For OBD seismic data imaging,the prerequisites of OBD seismic data imaging and the conventional imaging drawbacks were first analyzed,then the advantages of least square migration were inducted and taking the advantage of up-and down-going wave field easily to separate with OBD dual-senor data,a joint up-and down-going wave field least square reverse time migration was realized.The migration problems caused by uneven and low coverage in shallow parts and insufficient illumination of reflection were solved with this method.The improved imaging qualities of the synthetic and field datasets validated the proposed method.Based on these researches,a novel OBD processing concept has been proposed and a new more targeted processing flow has been built.Good results have been achieved with the novel processing concept and new processing flow. |
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