Dip-Constrained Tomography for Seismic Depth Imaging Accuracy
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Solution Overview
Problem
Current seismic imaging techniques face challenges in accurately locating oil and gas reservoirs due to non-linear and complex velocity model construction, particularly in correcting distortions caused by shallow heterogeneities and limited structural constraints, which result in pull-up and pull-down effects that affect depth imaging accuracy.
Innovation Solution
The introduction of an additional structural constraint in non-linear tomography techniques, specifically a dip-constrained approach, which corrects pull-up and pull-down effects by incorporating an offset-dependent dip constraint into the cost function to minimize misfit between migrated and expected dips, thereby improving depth imaging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If non-linear tomography techniques are used for velocity model construction, then imaging depth coverage is improved, but imaging accuracy deteriorates due to pull-up and pull-down effects caused by shallow heterogeneities
Solution Approach 1:
The patent applies local quality by introducing offset-dependent dip constraints that are specifically tailored to different offset ranges. The cost function incorporates dip constraints that vary with offset, allowing the velocity model to be adjusted locally in offset-dependent regions. This enables correction of pull-up and pull-down effects in specific areas without compromising the overall depth imaging capability, thereby improving imaging accuracy while maintaining depth coverage.
Solution Approach 2:
The patent changes parameters by introducing dip as an additional constraint parameter in the tomography cost function. Instead of relying solely on traditional traveltime residuals, the method incorporates dip measurements that are offset-dependent. This parameter change allows the inversion process to simultaneously optimize for both velocity model accuracy and dip consistency, resolving the contradiction between depth coverage and imaging accuracy.
2Measurement precision
If additional structural constraints are introduced in non-linear tomography, then depth imaging accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing dip measurements from migrated seismic data before the tomography inversion. The offset-dependent dip constraints are prepared in advance from the migrated image, which allows these constraints to be incorporated into the cost function without adding significant computational burden during the iterative inversion process. This preliminary preparation enables the use of additional structural constraints while managing computational complexity.
3Measurement precision
If dip-constrained inversion is applied to correct pull-up and pull-down effects, then localization precision of subsurface features is improved, but processing time increases
Solution Approach 1:
The patent applies self-service by utilizing dip information that is already present in the migrated seismic data. Rather than requiring separate dip measurement processes, the method extracts offset-dependent dip constraints directly from the migrated image, which has already been processed. This self-service approach allows the dip-constrained inversion to leverage existing data products, improving localization precision while minimizing additional processing time.
Data Source
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AI summary
Methods and systems for dip constrained non-linear tomography in seismic data. An additional term, comprising the dip associated with the kinematic migration of locally coherent events, is introduced into the cost function. The velocity is then updated to match the expected dip of the re-migrated offset-dependent events. Volumetric dip information can be automatically selected at a greater density in shallow locations, therefor complementing the lower density of the RMO events associated with shallow locations.