Seismic Quality Factor Q Model from Surface to VSP Receiver
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Solution Overview
Problem
Existing methods for seismic surveys fail to accurately derive seismic quality factor (Q) models for the overburden interval from the seismic source to the first useable downhole receiver, leading to incomplete correction for Earth's absorption in seismic data, which affects the resolution and accuracy of geologic feature identification.
Innovation Solution
A data processing system and method that uses vertical seismic profiles (VSPs) to estimate Q-values for the overburden interval by filtering and transforming seismic traces, determining spectral ratios, and generating a quality factor model that includes the entire seismic ray path from the surface to the downhole receiver, thereby improving the accuracy of inverse-Q filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If existing VSP methods are used to derive Q values, then Q values can be determined for subsurface intervals between downhole receivers, but Q values for the overburden interval from the seismic source to the first downhole receiver cannot be derived
Solution Approach 1:
The seismic ray path is segmented into two distinct intervals: the overburden interval (from surface to first downhole receiver) and the subsurface interval (between downhole receivers). Each interval is analyzed separately using appropriate methods, with the overburden Q derived from surface seismic data and the subsurface Q derived from VSP data, allowing complete coverage of the entire path
Solution Approach 2:
Surface seismic reflection data acts as an intermediary to provide the missing shallow Q-values for the overburden interval. By processing surface seismic data through spectral ratio analysis and applying constraints from VSP-derived Q-values at deeper levels, the method bridges the gap between surface and downhole measurements
2Ease of manufacture
If Q values are extrapolated from deeper logged intervals, then a complete Q model can be constructed, but the Q-values are less accurate because deeper intervals have higher Q values than shallow overburden
Solution Approach 1:
Different quality characteristics are applied to different depth intervals: shallow overburden Q-values derived from surface seismic data capture the lower Q values characteristic of near-surface formations, while deeper subsurface Q-values from VSP data reflect the higher Q values of deeper formations. This local differentiation eliminates the inaccuracy of uniform extrapolation
Solution Approach 2:
Surface seismic data is processed in advance to derive overburden Q-values before VSP processing. These pre-derived shallow Q-values serve as boundary conditions and constraints for the subsequent VSP analysis, ensuring that the complete Q model accurately represents both shallow and deep formation characteristics
3Productivity
If inverse-Q filtering is performed without accurate overburden Q-values, then processing can be completed, but the correction for Earth's absorption is incomplete, affecting resolution and amplitude analysis
Solution Approach 1:
The method merges surface seismic reflection data processing with VSP data processing to create a unified Q model that covers the entire seismic ray path from surface to downhole receivers. This combined approach ensures that inverse-Q filtering applies accurate absorption correction across all depth intervals, improving both resolution and amplitude analysis
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 more accurate removal of seismic absorption effects, resulting in higher resolution and better amplitude analysis of seismic data, and enhances the interpretation of geologic features by providing detailed and accurate Q models for surface seismic reflection data.
Implementation Method 1
The seismic source is typically located at ground surface. The seismic wave propagates into the ground, is reflected by subsurface formations, and returns to the surface where it is recorded by geophone sensors.
Implementation Method 2
The wave amplitude is attenuated during propagation, by an amount that is a function of travel time, signal frequency and the seismic quality factor, Q. This can also be referred to as a seismic attenuation factor. The effect can be referred to as Earth's absorption
Implementation Method 3
Q values can be determined from vertical seismic profiles (VSP's) using, for example, the spectral ratio method.
Data Source
AI summary
A method or system is configured for determining a seismic attenuation quality factor Q for intervals of subsurface formations by performing actions including receiving vertical seismic profile traces. The actions include filtering the vertical seismic profile traces with an inverse impulse response of a downhole receiver. The actions include transforming the vertical seismic profile data from the particle motion measured by the downhole receiver to the far-field particle motions represented by the source wavelet. The actions include determining a ratio of the spectral amplitudes of the direct arrival event of the transformed vertical seismic profile data and the source Klauder wavelet. A quality factor Q is generated representing an attenuation of the seismic signal between the source at ground level surface and the downhole receiver.