Subsalt Velocity Modeling via Basement Refraction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current methods, such as FWI-based refraction tomography, struggle to accurately determine velocity models for subsalt formations due to slower seismic velocities in sediments below salt formations, leading to insufficient refraction angles and incomplete data for seismic waves to return to the surface, and assume constant seismic propagation velocities in salt formations, which are often mixtures of salt and other materials.
Innovation Solution
A system utilizing a long offset between seismic source and receiver nodes, multiple seismic signals at different geographic locations, and the refraction of seismic waves off the basement's high-density material to create a three-dimensional velocity model, allowing for accurate seismic propagation velocity determination in both salt and subsalt formations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If FWI-based refraction tomography is used to determine velocity models for subsalt formations, then the method can handle larger amounts of input data and generate velocity models faster, but the seismic waves cannot return to the surface due to insufficient refraction angles caused by slower velocities in subsalt sediments
Solution Approach 1:
The patent introduces basement material as an intermediary element that enables seismic waves to return to the surface. The basement material acts as a mediator between the salt formation and the surface, providing the necessary refraction conditions for waves to turn back upward despite the slower velocities in subsalt sediments.
Solution Approach 2:
The patent changes the physical parameters of the seismic wave propagation by utilizing the high density and high seismic velocity of basement material. This parameter change creates sufficient refraction angles that allow waves to return to the surface, overcoming the limitation imposed by slower velocities in subsalt formations.
2Device complexity
If constant seismic propagation velocities are assumed in salt formations, then the velocity model generation is simplified, but the accuracy is reduced because salt formations are often mixtures of salt and other materials
Solution Approach 1:
The patent applies local quality by determining that different regions have different seismic propagation velocities. Specifically, the salt formation is distinguished from the basement material, with each region having its own velocity characteristics. This allows for more accurate velocity modeling that reflects the actual compositional variations.
Solution Approach 2:
The patent segments the subterranean formations into distinct regions (salt formation and basement material) with different seismic properties. This segmentation allows for independent velocity determination for each region, improving overall measurement precision while maintaining manageable model complexity.
3Quantity of substance
If seismic waves travel deeper into the earth to access subsalt formations, then more complete velocity model data can be obtained, but the refraction angle increases insufficiently to cause waves to turn upward without reflection
Solution Approach 1:
The basement material serves as an intermediary that facilitates the return of seismic waves to the surface. It provides the necessary refraction conditions at depth, enabling waves to turn upward and complete their journey to the surface without requiring additional reflection mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables the generation of accurate three-dimensional velocity models for salt and subsalt formations by leveraging the high-density basement material and extended offset distances to refract seismic waves effectively, overcoming limitations in existing methods.
Implementation Method 1
the refraction of seismic waves off the basement's high-density material to create a three-dimensional velocity model
Data Source
AI summary
The following disclosure relates to a system for generating velocity models of salt and subsalt formations. The system provides accurate velocities for both salt and subsalt formations. In some embodiments, the disclosure relies on the combination of three elements: the “long offset” between seismic source and seismic receiver node, the use of multiple seismic signals at different geographic locations, and the refraction of the seismic wave off of the “basement” of the earth's crust. By combining the multiple seismic signals with the “fast basement,” which is accessible due to the long offset of sources and receiver nodes, it is now possible to determine a more accurate seismic propagation velocity for salt and subsalt formations by using FWI-based refraction tomography.