Depth processing

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In areas with sharp vertical and lateral velocity changes, the time migration of seismic data does not allow obtaining a correct image of the environment. To improve reflection focus and restore true horizon geometry, PetroTrace specialists build depth-velocity models of any degree of complexity and use a wide range of pre-stack depth migration algorithms. Depth images calibrated to borehole data greatly improve the accuracy of subsequent structural and dynamic interpretation.

Building the initial velocity model

Velocity model refinement

Migration algorithms

Anisotropy

Extracting diffraction component of the seismic field

BUILDING THE INITIAL VELOCITY MODEL

An example of complex velocity model view.

A good match of the initial depth-velocity model with seismic data largely determines the quality and deadline of the depth migration.

Based on the analysis of all available a priori geological information and well data, PetroTrace specialists select the optimal approach for building the initial velocity model.

Many years of experience allows us to build a wide range of models: from simple gradient models to models with complex boundary topology and contrasting velocity layers, which enables us to effectively model such structural elements as salt bodies, intrusive bodies and thrust structures.

VELOCITY MODEL REFINEMENT

Results before and after refinement of the depth velocity model.

Obtaining a velocity model that well describes the observed seismic data is an important depth-processing task, since the quality of the final depth velocity model affects the migration result.

One criterion for depth velocity model quality is good straightness of in-phase axes on depth gathers after migration. The main data for refining the depth velocity model are residual kinematic moveouts, for the analysis and picking of which PetroTrace uses innovative interactive and automatic procedures.

PetroTrace specialists perform depth velocity model refinement using different methods, such as: controlled velocity inversion (Constrained Velocity Inversion); layer-by-layer and mesh 3D tomography, FWI.

MIGRATION ALGORITHMS

Comparison of 3D Kirchhoff depth migration (left) and 3D CRAM (right).

The features of the seismo-geological conditions of a particular area of work and the parameters of field observations dictate the choice of the optimal migration algorithm for solving the geological problems posed.

PetroTrace specialists have in their arsenal a complete set of migration transformation technologies based both on ray tracing and wave equation solutions. Extensive experience of application of various migration algorithms allows us to choose and recommend the most effective solution for optimal imaging of the environment in a particular geological setting, allowing us to meet even the tightest project deadlines.

ANISOTROPY

Seismic cube time slice and HTI anisotropy intensity.

Velocity anisotropy significantly affects the focusing and positioning of reflecting horizons after migration. PetroTrace specialists perform projects involving the determination and analysis of anisotropic Thomsen parameters for various types of anisotropic media (VTI, HTI, TTI) and the use of these parameters in migration transformations. Anisotropy-aware migration results have a higher resolution, improve the accuracy of tie-back to downhole data and increase the reliability of reservoir property predictions.

EXTRACTING DIFFRACTION COMPONENT OF THE SEISMIC FIELD

Example of a depth cube with an overlapped diffraction imaging result.

Information about the location of low-amplitude faults, fractures, karsts and other low-dimensional environmental elements can play a key role in the successful development of oil and gas fields. Traditional methods of localizing such elements, based on calculating various attributes from data after standard processing, are ineffective, since the goal of such processing is to obtain an optimal image of extended reflecting boundaries and small-sized elements of the medium can be completely lost in the processing. Meanwhile, such objects are often diffractors, and analysis of the scattered components of seismic waves can help to locate them.

However, the diffraction component of the seismic field carries much less energy than the reflected component and requires a special technology for its effective extraction. PetroTrace has developed and implemented its own technique for isolating the scattered component based on the 3-dimensional Radon transform, which allows us to successfully separate reflections and diffractions on depth-migrated seismograms in the angle domain. The energy cube of scattered waves, resulting from special adaptive pre-stack processing, helps to more confidently localize low-amplitude disturbances, fractures, karsts and other low-dimensional elements of the medium. Highlighting and mapping these elements allows you to refine interpretation, improve the reliability of geologic/hydrodynamic modeling and make more informed decisions about planning new wells.