Seismic Velocity Estimation via Virtual Receiver Interferometry
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Solution Overview
Problem
Existing vertical seismic profiling (VSP) methods face challenges in accurately determining seismic velocities in target areas below the depth of an existing wellbore, due to the lack of receiver arrays and the complexity of geologic formations with multiple layers of varying physical properties.
Innovation Solution
The method involves developing an improved velocity model by using a combination of VSP data processing techniques such as datuming, iterative wave equation migration, and seismic interferometry to create virtual sources and receivers, allowing for the computation of interferometric common shot and midpoint data, which enhances the accuracy of velocity models in the target area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If receiver arrays are placed only in the upper region above the target area, then the complexity of the survey is reduced and data collection is simplified, but the accuracy of velocity determination in the target area deteriorates
Solution Approach 1:
The patent creates virtual receiver arrays by applying seismic interferometry techniques. Virtual receivers are synthesized at locations below the physical receiver array using cross-correlation of seismic waves recorded at the physical receivers. This copying approach allows velocity determination in the target area without placing actual receivers there, resolving the contradiction between survey complexity and measurement precision.
Solution Approach 2:
The patent uses wavefield inversion and interferometry as intermediary processes to transfer information from the upper region where receivers are located to the target area where velocity determination is needed. The seismic waves act as carriers that convey information about subsurface properties through their interference patterns, enabling indirect measurement of velocities in the target area.
2Adaptability or versatility
If multiple layers with different physical properties are present in the geologic formation, then the realism and complexity of the formation model is improved, but the difficulty of determining seismic velocities increases
Solution Approach 1:
The patent employs iterative wavefield inversion that uses feedback loops to refine the velocity model. The process starts with an initial velocity model, computes wavefields, compares them with observed data, and adjusts the velocity model iteratively until convergence is achieved. This feedback mechanism enables accurate velocity determination in complex multi-layer formations by continuously refining the model based on observed seismic responses.
Solution Approach 2:
The patent segments the geologic formation into multiple layers with distinct physical properties and determines velocities for each layer separately using layer-specific seismic data and interferometry techniques. This segmentation approach allows the complex problem of velocity determination in heterogeneous formations to be broken down into manageable layer-by-layer analyses, improving both model realism and measurement accuracy.
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
This approach enables the precise determination of seismic event locations and velocities in the target area, improving the resolution and accuracy of VSP surveys by simulating VSP data at a deeper datum level, thereby enhancing the imaging and simulation capabilities for subterranean formations.
Implementation Method 1
The receiver converts the detected energy into signals which are then transmitted to a data collection location
Implementation Method 2
A seismic signal will travel faster through a dense formation than it will through a less dense formation
Implementation Method 3
Seismic interferometry utilizes the crosscorrelation of signal pairs to reconstruct the impulse response of a given media
Implementation Method 4
The receiver or receivers in the borehole receive seismic energy produced by the source. The seismic energy arrives at each receiver both as upgoing waves and as downgoing waves
Data Source
AI summary
A computer-implemented method includes providing a first velocity model obtained from a vertical seismic profile survey representative of an upper region of a subterranean formation. Wavefields from the first velocity model are datumed using wave equations to a datum line between the upper region and a target area beneath the upper region to obtain datumed wavefields. The method further includes obtaining interferometric common shot data and interferometric common midpoint data from the datumed wavefield using wave equations at the datum line. The first velocity model, the datumed wavefield, wavefield equations, and the interferometric common midpoint data are then used to generate a second velocity model representative of velocities in the target area.