Resonance-Impedance Model Corrects Sonic Logging Tool Bias
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Solution Overview
Problem
Current sonic logging techniques fail to accurately account for acoustic tool effects and near-wellbore alterations, leading to biases in estimating shear modulus c66 in anisotropic formations, especially in fast formations and small borehole diameters, which can result in incorrect hydrocarbon reservoir identification and location.
Innovation Solution
A resonance-impedance model is used to account for acoustic tool effects by modeling the tool structure with an equivalent surface impedance, allowing for the correction of biases in shear modulus c66 calculations and providing accurate radial profiles of shear velocities across a range of frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional sonic logging techniques are used to measure formation properties, then the measurement process is simple and fast, but the measurement precision is degraded due to unaccounted acoustic tool effects and near-wellbore alterations
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing look-up tables containing formation property values (including shear modulus c66) for various combinations of tool parameters and formation characteristics before actual logging operations. During data processing, the measured Stoneley dispersion data is compared against these pre-computed look-up tables to rapidly identify the best-matching formation properties, eliminating the need for complex real-time iterative calculations while maintaining high precision in shear modulus estimation even in fast formations and small boreholes
Solution Approach 2:
The patent introduces an intermediary effective tool model that accounts for acoustic tool effects and near-wellbore alterations. This model serves as a mediator between the raw measured Stoneley dispersion data and the final formation property estimates. The model includes look-up tables that pre-characterize the tool's acoustic response under various conditions, allowing the processing system to compensate for tool-induced biases without requiring complex forward modeling during actual data processing, thus improving measurement precision while controlling computational complexity
2Reliability
If acoustic tool effects are not accounted for in data processing, then the processing is faster and simpler, but the reliability of formation property estimation deteriorates due to biases in shear modulus c66 calculations
Solution Approach 1:
The patent applies preliminary action by pre-computing and storing look-up tables that contain formation property values (including shear modulus c66) for various combinations of tool parameters, borehole diameters, and formation characteristics. During actual logging operations, the measured Stoneley dispersion data is compared against these pre-computed tables to rapidly identify the best-matching formation properties. This approach ensures reliable hydrocarbon reservoir identification by accounting for tool effects while minimizing processing time through efficient table lookup rather than complex real-time calculations
Solution Approach 2:
The patent employs parameter changes by utilizing pre-computed look-up tables that store formation properties across a range of parameter values (tool frequencies, borehole diameters, formation velocities). The data processing system efficiently searches through these tabulated parameter combinations to find the best match for the measured data, thereby achieving reliable formation characterization including accurate shear modulus estimation without requiring time-consuming iterative parameter optimization during actual logging
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 approach enables precise estimation of shear modulus c66, improving the accuracy of hydrocarbon reservoir identification and location by accounting for tool and near-wellbore alterations, enhancing the reliability of seismic prospecting and logging while drilling operations.
Implementation Method 1
A resonance-impedance model is used to account for acoustic tool effects by modeling the tool structure with an equivalent surface impedance
Implementation Method 2
modeling the tool structure with an equivalent surface impedance, allowing for the correction of biases in shear modulus c66 calculations
Implementation Method 3
An acoustic source in a fluid-filled borehole generates headwaves, as well as relatively stronger borehole-guided modes
Implementation Method 4
The headwaves are caused by the coupling of the transmitted acoustic energy to plane waves in the formation that propagate along the borehole axis. An incident compressional wave in the borehole fluid produces critically refracted compressional waves in the formation
Implementation Method 5
A standard sonic measurement system consists of placing a piezoelectric source and hydrophone receivers inside a fluid-filled borehole
Implementation Method 6
A standard sonic measurement system consists of placing a piezoelectric source and hydrophone receivers inside a fluid-filled borehole
Data Source
AI summary
Methods and apparatus facilitating radial profiling of shear slowness are disclosed. According to some aspects of the invention, acoustic tool bias is accounted for in the calculation of radial profiles. According so some aspects, acoustic tool bias is accounted for by replacing acoustic tool structure with a resonance-impedance model. The resonance-impedance modeling according to principles of the present invention is applicable to vertical, deviated, and horizontal boreholes.