Wavefront Slowness Determination Using 3D Coherence Analysis
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Solution Overview
Problem
Current methods for determining slowness of a wavefront as it propagates along a receiver array are inadequate for accurately characterizing well placement and reservoir features, particularly in identifying changes in layer velocity and detecting drilling hazards like high pressure zones or faults.
Innovation Solution
The method involves transmitting signals from sources spaced around a downhole tool receiver array, processing waveform data to filter out direct arrivals, and constructing a three-dimensional slowness-time coherence representation to identify parameters of non-direct wavefronts, including refracted and reflected arrivals, using techniques like common source gather filtering and semblance modification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current methods are used to determine slowness of wavefronts, then the measurement process is simple, but the accuracy for characterizing well placement and reservoir features is insufficient
Solution Approach 1:
The patent segments the wavefront detection process into distinct components: direct arrival identification, non-direct arrival extraction, and slowness calculation. By separating these functions and processing them independently through specialized algorithms (such as semblance modification and coherence analysis), the system achieves high measurement precision while managing computational complexity through modular processing stages.
Solution Approach 2:
The patent transitions from traditional one-dimensional slowness measurement to three-dimensional slowness determination by analyzing wavefronts in multiple spatial dimensions. This involves computing slowness vectors with components in different directions (radial, azimuthal, and vertical) and using multi-component receiver arrays to capture wavefront characteristics across three-dimensional space, thereby significantly improving reservoir characterization accuracy.
2Measurement precision
If direct arrivals are included in the waveform data, then the data completeness is high, but the interference from direct arrivals reduces the detection accuracy of non-direct wavefronts
Solution Approach 1:
The patent extracts and removes direct arrival components from the total waveform data through semblance modification and coherence-based filtering. By identifying the characteristic patterns of direct arrivals (such as tool-borne waves and borehole-guided waves) and systematically eliminating them, the system isolates non-direct wavefronts for accurate analysis, thereby improving detection precision without requiring complete data retention.
Solution Approach 2:
The patent introduces intermediary processing steps including wavelet transforms, cross-correlation analysis, and coherence calculations that act as mediators between the raw waveform data and the final slowness determination. These intermediary processes enable the system to separate direct and non-direct arrivals by analyzing their different temporal and spatial coherence characteristics, allowing accurate extraction of non-direct wavefront information.
3Measurement precision
If a three-dimensional slowness representation is computed, then the reservoir characterization capability is improved, but the computational processing time increases
Solution Approach 1:
The patent performs preliminary processing actions including pre-computing slowness-time coherence representations, pre-identifying direct arrival patterns, and pre-establishing filtering criteria before the main slowness determination process. By preparing these computational structures in advance and using efficient algorithms for coherence calculation and slowness vector computation, the system reduces the overall processing time required for three-dimensional slowness analysis while maintaining high measurement precision.
Data Source
AI summary
Methods and apparatus for determining slowness of wavefronts. An example apparatus includes one or more sources spaced from a receiver. The one or more sources are to transmit one or more signals and the receiver is to receive at least a portion of the one or more signals. The apparatus includes a processor to process waveform data associated with the one or more signals by stacking waveforms of the waveform data based on to linear moveout and sinusoidal moveout.