VSP-CMP Gathers via Wavefield Extrapolation
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Solution Overview
Problem
Pre-stack elastic inversion and time-domain imaging methodologies for vertical seismic profiling (VSP) data have not been fully developed, limiting the analysis and evaluation of subsurface structure and formations compared to surface seismic survey data.
Innovation Solution
A computer-implemented method and system for generating VSP-CMP gathers through wavefield extrapolation using measured Green's functions derived from direct arrivals, convolved with upgoing and cross-correlated with downgoing wavefields, to assemble and process vertical seismic profiling survey data for subsurface formation analysis.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional VSP processing methods are used, then the measurement precision of subsurface formation analysis is limited, but the device complexity and processing methodology development remain insufficient compared to surface seismic surveys
Solution Approach 1:
The patent introduces an intermediary processing system that converts VSP data into pseudo-CMP gathers format. This intermediary representation allows traditional surface seismic processing algorithms to be applied to VSP data, bridging the gap between the two different data acquisition methods and enabling sophisticated subsurface analysis without requiring entirely new processing methodologies.
Solution Approach 2:
The patent transforms VSP data by changing its fundamental parameters and organization structure. By reorganizing the data into pseudo-common midpoint gathers with appropriate time and spatial parameter transformations, the data becomes compatible with established surface seismic processing workflows, thereby improving measurement precision without proportionally increasing complexity.
2Measurement precision
If sensor spacing in VSP is reduced to improve resolution, then the measurement precision of reservoir characterization improves, but the quantity of data and processing requirements increase
Solution Approach 1:
The patent merges multiple VSP receiver measurements into pseudo-CMP gathers that simulate surface seismic data organization. By combining the high-resolution information from closely-spaced wellbore sensors into a format that aggregates data by common midpoint, the method preserves the detailed resolution information while reducing the effective data quantity that needs to be processed through sophisticated algorithms.
3Loss of time
If VSP data is processed using conventional methods, then the processing time is reduced, but the loss of information about subsurface structure and formations increases
Solution Approach 1:
The patent performs preliminary transformation of VSP data into pseudo-CMP gathers format before applying standard processing algorithms. This preliminary action prepares the data in advance in a format that is optimized for extracting subsurface structural information, ensuring that when conventional processing methods are applied, they can fully utilize the available information without loss.
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 extraction of detailed information about subsurface formations, enhancing the resolution and lateral coverage of VSP data, similar to surface seismic data, by converting upgoing and downgoing wavefields into pseudo common mid-point gathers, allowing for physical parameter extraction such as acoustic impedance and velocity ratios.
Implementation Method 1
A measured VSP Green's function is derived in the computer from the direct arrivals of seismic energy in the vertical seismic profiling survey for individual surface locations and then used to extrapolate the vertical seismic profiling upgoing wavefield data to the surface
Implementation Method 2
The derived Green's functions for the individual surface locations are then convolved with upgoing wavefields of the seismic energy from the surface locations sensed by the individual receivers
Implementation Method 3
The derived Green's functions for the individual receivers are also cross-correlated with downgoing wavefields of the seismic energy emitted from other surface locations
Data Source
AI summary
Direct arrivals from walkaway vertical seismic profiling or VSP survey data are used to derive Green's functions representing the seismic wave amplitude and travel time information required to extrapolate the vertical seismic profiling survey data from individual wellbore receivers to the individual source locations. The derived Green's functions are employed in a convolution process with upcoming primary wavefields from the VSP survey data for other surface locations. The derived Green's functions are also used in a correlation process with downgoing wavefields from the VSP survey data to extend lateral coverage of the VSP image. The sets of VSP-CMP gathers so formed are then processed to obtain information about the subsurface formations.