Study On Offshore Seismic Acquisition Technology In KL Weak Reflection Area Of Bohai Oilfield

Conventional 3D seismic acquisition basically meets the needs of stereo exploration for large and medium-sized structure in almost each oilfield.However,with the development of the exploration and production,the geological target which we faced is becoming more and more complicated.No matter structural oil-gas reservoir or subtle reservoirs put forward higher demands on S/N ratio,resolution ratio,fidelity and imaging accuracy on seismic data.The current conventional seismic acquisition technology can not satisfy the fine exploration and production requirements.From 2006 Bohai oilfield accelerates the progress of the offshore seismic acquisition,the primary 3-D seismic exploration almost accomplished by 2013.The seismic word has played an important role in Bohai exploration and production.Today Bohai oilfield has entered the fine exploration stage,with comprehensive analysis of the existing seismic data for different geological problems,there are obvious phenomenon of narrow band,lack of resolution,lack of low frequency information and middle deep energy deficiency on partial seismic data.The data can not fulfil the requirements of fine exploration research.The primary seismic survey is offshore towed-streamer in KL area,Bohai oilfield.Be restricted by equipment,technology and method at that time,the quality of the seismic data is poor with lower S/N ratio,discontinuous seismic event and random reflection character.Although corresponding processing technique for tapping the potential is used,the re-processed data is still unable to meet the requirements.High density seismic acquisition is a new technology which developed in recent years.It can realize uniform illumination of the geological and continuous sampling of the seismic wave-field through high density spatial sampling,improve the S/N ratio,resolution and imaging precision.The article analyze the insufficient of the conventional towed-streamer acquisition parameter according to the offshore seismic data in KL weak reflection area,study on seismic acquisition geometry parameter and air-gun source parameter,including maximum offset,bin size,fold seismic source volume and gun depth,develop a method of seismic acquisition parameter optimization for offshore high density survey.The main method to improve lower S/N ratio of the seismic data in weak reflection area is to improve the original S/N ratio,which is the foundation to solve the problem in weak reflection area.When the original S/N ratio is lower than 1/6,there hardly any way to improve the S/N ratio in seismic data processing.The noise from the air-gun source is the bubble effect when the air-gun shooting on the line.The noise from the receiver is the current noise because of the poor coupling between the receiver and the sea bottom.To improve the primary S/N ratio of the seismic data,the article study on restricting the bubble effect to improve the P/B ratio start with air-gun source optimization design,Also study on methods to restrict the noise from the receiver and to improve the S/N ration on seismic data by improve the degree of the coupling.Through this study,utilize ocean bottom cable with high density geometry,the trace density at least 6 times of the conventional towed-streamer,the bin size should be less than or equal to 12.5m×25m,the air-gun source is larger than 3000 cu.in,the P/B ratio NBE 25,then the seismic data imaging quality can be effectively improved.