Static Corrections Methods in the Processing of Deep Reflection Seismic Data

Statics are big challenges for the processing of deep reflection seismic data. In this paper several different statics solutions have been implemented in the processing of deep reflection seismic data in South China and their corresponding results have been compared in order to find proper statics solutions. Either statics solutions based on tomographic principle or combining the low-frequency components of field statics with the high-frequency ones of refraction statics can provide reasonable statics solutions for deep reflection seismic data in South China with very rugged surface topography, and the two statics solutions can correct the statics anomalies of both long spatial wavelengths and short ones. The surface-consistent residual static corrections can serve as the good compensations to the several kinds of the first statics solutions. Proper statics solutions can improve both qualities and reso- lutions of seismic sections, especially for the reflections of Moho in the upmost mantle.

Identification and Correction for MT Static Shift Using TEM Inversion Technique

The inversion of TEM data, using the observed magnetic fields instead of that of apparent resistivities data in this paper, avoids the errors caused by the definition of the apparent resistivity. The inversed results by fitting the magnetic fields of the transmitter source's image with the observed magnetic fields are relatively less affected by the conductivity inhomogeneity. The MT apparent curve is calculated on the basis of the conductivity model constructed from the TEM inversion results. This curve is used as a reference curve for the correction of MT static shift, which makes the correction more reliable. Meanwhile, the domain transformation is also achieved from time to frequency between the two kinds of electromagnetic data. Therefore, the correction of the MT static shift is actualized using TEM inversion method. The corresponding application research shows that this method is very effective for the identification and correction of the MT static shift.

Near-Surface Correction on Seismic and Gravity Data

It is important and urgent to work out better statics correction methods to facilitate seismic prospecting. This paper presents a new method of statics correction calculation based on development of a seismic-gravity model of the near surface. Gravity interpretation includes determination of the local component caused by the near surface effects and calculation of the near-surface rock density by solving the linear inverse gravity problem. To obtain the near-surface velocities, priori seismic data such as time fields of the first waves recorded in the initial part of common depth point（CDP） seismograms are used. An optimal near-surface model is retrieved on the basis of the successive solution of the inverse and forward seismic problems, correlating with the observed seismic data. Matching of seismic and gravity model of the near surface yields the maximum coefficient of correlation between the values of velocities and densities. At the end of the interactive iterative process we get values of the near-surface seismic wave velocities, used for statics evaluation, and values of gravity anomalies, calculated with a variable density of the interbedded layer. The applications of the proposed method at geophysical exploration of oil and gas confirm the possibility of calculation of statics correction using the gravimetric data by constructing a coherent seismic-gravity model of the near surface.

A Layer-Stripping Method for 3D Near-Surface Velocity Model Building Using Seismic First-Arrival Times

In order to improve the efficiency of 3D near-surface velocity model building, we develop a layer-stripping method using seismic first-arrival times. The velocity model within a Common Mid-Point （CMP） gather is assumed to be stratified into thin layers, and the velocity of each layer var- ies linearly with depth. The thickness and velocity of the top layer are estimated using minimum-offset first-arrival data in a CMP gather. Then the top layer is stripped and the second layer becomes a new top layer. After removing the effect of the top layer from the former first-arrival data, the new first-arrival data are obtained and then used to estimate the parameters of the second layer. In this manner, the velocity model, being regarded as that at a CMP location, is built layer-by-layer from the top to the bottom. A 3D near-surface velocity model is then formed using the velocity models at all CMP locations. The tests on synthetic and observed seismic data show that the layer-stripping method can be used to build good near-surface velocity models for static correction, and its computation speed is approximately hundred times faster than that of grid tomography.