Is the constant velocity of a single layer (which can be very thin).
![promax seismic promax seismic](https://cf.ppt-online.org/files/slide/g/GfRxveUONFEqt9XBPZc4CY65m3DHhyJl2boQ0w/slide-31.jpg)
Referring to definitions shown in the adjacent figure: V int Nevertheless seismic velocity is often used for depth conversion and migration purposes and can be calibrated to well information or used where well information is particularly sparse. Generally is its correct to stack the data with seismic velocity but little else. Sheriff and Geldart show further diagrams illustrating the typical trends of velocity with various parameters. Carbonates in particular show a large range in velocities depending on porosity. The adjacent figure summarises typical velocities for differing lithologies and porosities. Fluids within pores tend to make the rocks less compressible and lead to higher interval velocities for P-waves. Sediment velocities generally increase with depth due to increased pressure of the overburden. Seismic measurements of velocity are averaged over the horizontal distance through which the seismic energy travels. A zero-offset VSP or checkshot survey will measure the vertical velocity in the vicinity of the well. Seismic measurements are typically 5-10% faster.Ī sonic log measures the velocity variation in depth as seen immediately adjacent to the borehole. Anisotropy is also used to refer to the difference between well velocities (vertical measurements) versus seismic velocities (horizontal measurements). The CMP method generally ignores mode conversions and anisotropy (variation of a property with direction of measurement). In horizontally layered media such as shales the transverse anisotropy may cause the velocity to vary as much as 20% depending on dip. It is generally considered that velocity picking is an art. Velocity analysis is often carried out several times during processing resulting in an iterative improvement of velocity estimation. It is also probably the most critical stage since the velocity analysis is an initial interpretation of the data and it is important that the seismic interpreter is involved in the analysis and quality control stages. Nevertheless, velocity analysis is still one of the most time consuming parts of seismic processing.
![promax seismic promax seismic](https://html.pdfcookie.com/02/2019/12/31/g27ozx37z0v0/bg16.jpg)
Several velocity analysis methods have been used in the past but today most velocities are picked interactively using combination displays on processing workstations. In this section we define several types of velocity commonly used in seismic processing and concentrate on methods used to determine and quality control velocity analysis. For a single flat layer the shape of the moveout curve is defined by the hyperbolic relationship between zero-offset time and velocity. The CMP method, NMO and the concept of stacking velocity was introduced in a previous discussion. Interactive Velocity Analysis explanation of sample display preconditioning, analysis interval, moveout stretch. VELOCITY ANALYSIS in practice version 1.0 released 29/1/99ĭefinition of velocities e.g.