XMF

Kinematic Seismic Model Fitter

XMF (Kinematic Seismic Model Fitter) completes XTomo product line of software tools for solving two-dimensional seismic kinematic inverse problem. While XTomo-LM, the main product of the line, implemented different inversion algorithms, XMF offers a workframe for "manual" layered model fitting by criterion of visual proximity of computed TX-curves to phase lineups on seismograms. Despite technological inferiority (to compare to inversion algorithms), that approach is universal and do not impose high requirements on observation data. Therefore, it is widely applied in seismic practice. In a sense, XMF complements XTomo-LM, and together they form a powerful means of kinematic interpretation.

xmf txFig. 1. Seismograms with computed traveltime curves displayed by the Line Seismogram Viewer module.

XMF input data include a set of common source point seismograms, registered on a seismic line, and positional information written in seismogram trace headers or supplied in text files. Seismograms are represented by seismic files of SEG-Y/PC format (i.е. SEG-Y adapted to the x86/Windows platform).

To represent the layered model, XMF uses a single two-dimensional curvilinear grid stretched on a wireframe of non-intersecting seismic horizons. Velocity function is defined at grid nodes, while horizons coincide with some of grid lines. After the user creates or edits the wireframe, XMF stretches velocity grid automatically. The initial model has constant layer velocities.

The XMF framework organizes fitting a model as  a sequence of iterations. Each iteration includes the following actions:  

  • editing the model;
  • binding reflections or/and head waves to layers (i.e. to horizons flooring layers);
  • solving kinematic forward problem (i.e. ray-tracing with computing traveltimes along rays);
  • studying ray picture;
  • studying computed TX-curves drawn over the seismograms.

The key components of the XMF environment are:

  • Line seismogram viewer  allows viewing multiple seismograms, in particular, scrolling of seismogram views along the line with the arrow buttons, as on fig. 1. The user can adjust trace display and amplitude control and perform reducing seismic record with given reduction velocity.
  • Graphic model editor consists of two components: geometry editor and velocity editor. The former allows editing model wireframe, i.e. change shape and position of model horizons. The latter provides for editing velocity, in particular, changing velocity profiles (i.e. velocity grid columns) in numeric form with further continuation velocity from a column to the entire grid or its part. Both editors are equipped with tool kits for effective work.

  • Forward Problem Solver traces rays of diving, reflected and head waves. FPS traces rays for a user-defined samples of waves and sources, concurrently for several sources. The result is in the Ray Catalog database optimized for fast access to individual rays and ray paths.
  • Ray Picture Viewer (RPV) provides viewing ray picture by ray samples, which the user composes using meaningful criterions.

  • Line Seismogram Viewer (LSV) not only provides for viewing seismograms, but also draws TX-curves on top of seismic record and enables the user to control curve visibility and their drawing attributes.

The important XMF feature is a tool for examination of ray samples matching TX-curve points on specified rectangular of a seismogram as shown on fig. 2. On the snapshot, the LSV and RPV windows are displayed. A rectangle on seismogram is selected with the rubber-band; the selected menu command launch RPV, which displays the rays matching exactly the TX-curve points within the rubber-band. The feature helps to bind a TX-curve segment that deviates from a phase line-up to a segment of a seismic boundary or (for diving wave) to a segment of velocity vertical profile and, in this way, helps the user to correct the model properly.

xmf tx raysFig. 2. Ray sample matching traveltime curve points from a specified rectangle domain of a seismic record.

XMF и XTomo-LM. Though XMF is a self-contained application, it was conceived from the very beginning as a complement to XTomo-LM in order to append it with a convenient platform of manual model fitting and thereby to get a powerful means of kinematic interpretation, which is capable of dealing with observed data of different completeness and quality. Because both applications are rather "heavy", it is better to speak of joint processing.  Technically, this is implemented as a bidirectional interface between the two applications on the project level. That means that, having started interpretation process in an XTomo-LM project, the user can continue it at any moment, in a new XMF project and vice a versa. The interface is feasible in releases XTomo-LM 3.4.1 and XMF 1.1.1 and later.