In-situ Seismic Velocity-Stress Relation Determination
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Solution Overview
Problem
Current methods are complex and inefficient for determining the relation between seismic velocity and the state of stress in underground formations, particularly under time-changing surface loading conditions, as they require complicated derivations of long-distance seismic velocities.
Innovation Solution
A method involving selecting a relation between seismic velocity and stress with unknown parameters, determining seismic velocities at different times, converting surface loading changes into stress changes, and calculating these parameters to establish the seismic velocity-stress relation in-situ.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If sonic logging techniques are used to measure seismic velocity, then local velocity can be obtained, but it requires complicated derivations to obtain long-distance seismic velocities
Solution Approach 1:
The patent replaces the mechanical/physical measurement approach of sonic logging with a seismic wave-based measurement system. By using seismic sources and receivers to directly measure travel times over long distances, the method obtains long-distance seismic velocities without requiring complicated mathematical derivations from local sonic measurements. This substitution of measurement methodology directly resolves the contradiction between measurement capability and derivation complexity.
2Reliability
If time-lapse seismic surveys are conducted to monitor reservoir changes, then reservoir status can be tracked, but the relation between seismic velocity and stress state must be accurately determined
Solution Approach 1:
The patent utilizes changes in surface loading conditions as a natural experiment to induce stress state changes in the formation. By measuring seismic velocity changes corresponding to these known stress changes, the method determines the velocity-stress relationship parameters. This approach transforms the difficult measurement problem into a more manageable parameter determination problem through controlled natural variations, thereby improving monitoring reliability while reducing measurement difficulty.
Solution Approach 2:
The method employs an iterative feedback process where initial velocity-stress relations are used to interpret seismic data, which then feeds back to refine the velocity-stress relation model. This feedback mechanism allows for progressive improvement in the accuracy of the velocity-stress relationship determination, resolving the difficulty of obtaining accurate relations needed for reliable reservoir monitoring.
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 method simplifies the determination of the seismic velocity-stress relation, allowing for accurate modeling of underground formations under changing conditions, enhancing the accuracy of time-lapse seismic surveys and reservoir monitoring.
Implementation Method 1
The seismic velocity is the propagation rate of a seismic wave through the underground formation
Implementation Method 2
converting the difference in surface loading conditions at the two times in a difference in states of stress in the underground formation
Data Source
AI summary
A method of determining in-situ a relation between the seismic velocity and the state of stress in an underground formation located under a surface subjected to time-changing surface loading conditions. A relation is selected between the seismic velocity and the state of stress containing at least one unknown parameter. A seismic source is arranged at surface or in a borehole penetrating the underground formation, and a seismic receiver is arranged at a distance from the seismic source at surface or in a second borehole. At two different times the seismic velocity of the formation along a path from the seismic source to the seismic receiver is determined. The difference in surface loading conditions at the two times is converted in a difference in states of stress in the underground formation. The unknown parameter(s) are calculated to obtain the relation between the seismic velocity and the state of stress in the underground formation.