Application Of Structure Model Building And Velocity Field Construction In Kelasu Tectonic Belt

Kelasu tectonic belt in Kuqa Depression is a major zone of natural gas exploration in Tarim basin. Due to its complicated subsurface geological structure, it is very difficult to build reasonable structure model and correct velocity field. Moreover, the above two factors restrict the discovery of the traps and reservoirs further. Aiming to the reasonable structure model building and correct velocity field construction, this paper adopt corresponding methods in the application and the implement means in Kelasu tectonic belt .Kelasu tectonic belt is a foothill thrust belt, which has strong overthrust nappe. For its low signal to noise ratio and general data of low quality, it is difficult to describe the complicated subsurface geological structure. Seismic-geologic comprehensive calibration is the basement of building a structure model, as a good reference for seismic-geologic comprehensive calibration of the subsurface geological structure, surficial structure of Kelasu tectonic belt have been finely calibrated by the using of geological profiles and remote sensing images. The structure of Kelasu tectonic belt and salt rock are closely related, through fine description of the salt rock's development, together with the analysis of fault-related fold theoretic, a five sectional structure model of Kelasu tectonic belt has been built. In order to make sure the structure model is reasonable and reliable, a series of technical means have been used during the procedure of structure modeling, such as joint interpretation of seismic and non-seismic, forward modeling, numerical simulation, integration of processing and interpretation, balanced section technique, and so on.Correct variable velocity mapping is the main target of building a velocity field construction. Interval velocity filling method velocity-field-built is very useful for foothill thrust belt, whose core is to acquire interval velocity correctly. Aiming to the correct change gradient of interval velocity in different parts of the structure, drilling velocity and seismic velocity have been analyzed by iteration model, forward analysis and cycle analysis. On the basement of the structure model, together with the correct interval velocity, a proper velocity field has been constructed, and the variable velocity mapping has been completed reasonably and correctly further.Through the study of this subject, Kelasu tectonic belt's sectional structure model has been set up; the understanding of Kelasu tectonic belt has been deepen; a series of traps has been discovered and implemented; a number of favorable targets and well locations have been suggested by through comprehensive evaluation; Dabei3 and Keshen2 gas fields have been discovered, and each one's reserve is above one hundred billion cubic meters; and Dabei gas field has received good exploration assessment. At the same time, the technic of the build of reasonable structure model and correct velocity field in complex foothill area have been developed and refined practically.