Velocity Model Building In Palaeozoic Erathem And Effect Analysis In The South Yellow Sea

Seismic velocity is one of the most important parameters. And the precision of seismic velocity should be improved further to enhance the exploration accuracy of South Yellow Sea basin. A series of problems exist during the access of velocity in study area, such as low level of exploration, poor data of seismic profiles, maldistribution of drills which are less and shallow, and the difficulty of using existing logging data. Improving the velocity precision will meet some difficulties, so a velocity model building method of high precision and high efficiency should be searched in order to resolve the problem that velocity in study area has a larger error.The paper researches the staple velocity model building methods and the present situation of velocity usage in South Yellow Sea basin. And it introduces the fundamental data about general exploration situation, areal geology, sequence stratigraphical classification, wave field characteristics, sedimentary characteristics, drilling data and horizon interpretation. On the basis of theoretical research about seismic velocity, a velocity error method by correcting stacked velocity is illustrated as an emphasis.Velocity model building is on the basis of variation rule of seismic wave velocity and makes a reference to strata sequence. Firstly, elicit the stacked velocity of seismic profiles which have poor reflection by using the stacked velocity of seismic profiles which have better reflection and elicit the stacked velocity of area having not surveying lines by using the stacked velocity of area having surveying lines. As a result, a stacked velocity spectrum of the whole area can be got. Secondly, elicit the average velocity of drills by using every depth of drill and the To in horizon interpretation, which can be used to correct average velocity acquired by inversion of stacked velocity. During the correction, the velocity of Paleozoic Erathem can be got by the variation rule of the difference value between above-mentioned two kinds of average velocity. And the average velocity model of higher accuracy can be built. At last, this model is transformed layer velocity model.This method corrects the velocity of Paleozoic Erathem well and improves the precision of original velocity recording greatly. The paper illustrates the model building details, such as the format of model building data and available methods, the coordinate system of model building, the correction of data, the velocity data correction method in Paleozoic Erathem stratum, and the computed result feedback on model. In addition, the paper analyses the velocity of main stratums.According to the above-mentioned model building method, a velocity model adapted to South Yellow Sea basin is built for the first time. Using this model, this paper makes Time-depth conversion and draws South Yellow Sea basin geology tectonic maps of higher accuracy.