NMR Caliper Borehole Geometry Measurement
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Solution Overview
Problem
Conventional logging while drilling (LWD) calipers face limitations in providing consistent and dependable measurements across various mud types and conditions, including high barite muds and washout conditions, due to sensitivity to mud properties and limited depth of investigation range.
Innovation Solution
A nuclear magnetic resonance (NMR) caliper system with multiple coils is coupled to a borehole assembly, conducting NMR scans to determine borehole geometry by generating RF pulses and measuring T2 distributions, which are used to calculate borehole dimensions and porosity, allowing for accurate measurements independent of mud types.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional LWD calipers (ultrasonic, density, neutron, or resistivity) are used, then borehole geometry measurements can be obtained, but the measurements become sensitive to mud properties and cannot provide consistent results across different mud types
Solution Approach 1:
The patent replaces conventional mechanical and acoustic measurement systems (ultrasonic calipers, density calipers, neutron calipers, resistivity calipers) with an optical system that uses laser illumination and photodetectors to measure borehole geometry. This substitution eliminates sensitivity to mud acoustic properties and enables consistent measurements across all mud types including air, gas, oil, and water-based muds.
2Measurement precision
If conventional ultrasonic calipers are used, then good precision azimuthal hole shape definition can be achieved, but the measurements require known acoustic properties of mud and sufficient acoustic impedance contrast
Solution Approach 1:
The patent replaces the ultrasonic acoustic measurement system with an optical measurement system using lasers and photodetectors. This substitution eliminates dependency on mud acoustic properties and acoustic impedance contrast, allowing precise azimuthal hole shape definition regardless of mud type.
3Measurement precision
If density and neutron based measurements are used, then non-directional caliper information can be obtained, but azimuthal information cannot be obtained when the tool is sliding
Solution Approach 1:
The patent replaces density and neutron measurement systems with an optical system that uses multiple photodetectors arranged to detect light reflected from different azimuthal positions around the borehole. This optical system can determine azimuthal hole shape even when the tool is sliding and not rotating, eliminating the limitation of conventional systems.
4Measurement precision
If propagation resistivity tools are used, then good quality caliper information can be obtained in water based muds, but the tools cannot provide consistent measurements across various mud types and conditions
Solution Approach 1:
The patent replaces resistivity measurement tools with an optical measurement system using lasers and photodetectors. This substitution enables consistent high-quality caliper measurements across all mud types including water-based, oil-based, air, and gas muds, as well as in washout conditions where resistivity tools fail.
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
The NMR caliper system provides consistent and accurate borehole geometry measurements across different mud types and conditions, enhancing the reliability of LWD data by calibrating against mud properties and extending the depth of investigation range.
Implementation Method 1
A nuclear magnetic resonance (NMR) caliper system with multiple coils is coupled to a borehole assembly, conducting NMR scans to determine borehole geometry by generating RF pulses and measuring T2 distributions
Implementation Method 2
conducting NMR scans to determine borehole geometry by generating RF pulses and measuring T2 distributions, which are used to calculate borehole dimensions and porosity
Data Source
AI summary
A method and system for determining a geometry of a borehole includes forming an nuclear magnetic resonance (NMR) caliper with a plurality of coils and coupling the NMR caliper to a borehole assembly. The NMR caliper may be calibrated for porosity and the T2 of the drilling mud, prior to drilling, at the surface. After drilling commences, scans of the borehole may be conducted with each coil of the NMR caliper. Each scan may include propagating RF energy across a range of frequencies with each coil in order to excite a NMR signal at varying depths. Borehole wall distances from the NMR caliper may be determined by reviewing a plurality of T2 distributions from CPMG measurements derived from the scans. In some embodiments, borehole wall distances from the NMR caliper may be determined by reviewing porosity values derived from the scans.