Oil Saturation Logging via NMR and Pulsed Neutron Integration
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Solution Overview
Problem
Existing well logging techniques, such as pulsed neutron and carbon/oxygen logging, are impractical or unreliable for reservoirs with low or variable salinity fluids, and lack the accuracy to provide a granular representation of oil saturation variations across a hydrocarbon reservoir.
Innovation Solution
A method involving continuous oil saturation logging using a combination of Nuclear Magnetic Resonance (NMR) viscosity logging, temperature logging, and pulsed neutron logging to generate a continuous oil saturation log, accounting for variations in rock and fluid properties by determining oil API gravity, density, and carbon-oxygen ratios, which are then used to calculate oil saturation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If pulsed neutron capture logging is used to assess reservoir saturation, then the method is suitable for reservoirs with high salinity fluids, but it becomes impractical or unreliable for reservoirs with low or variable salinity fluids
Solution Approach 1:
The patent combines multiple logging methods (NMR, C/O, and temperature logging) into a unified approach that can reliably measure oil saturation across diverse reservoir conditions including low, high, and variable salinity fluids. The integrated system uses NMR for primary saturation measurement, C/O for carbon-oxygen ratio analysis, and temperature data for property corrections, making the overall method universally applicable regardless of fluid salinity.
Solution Approach 2:
The patent introduces an intermediary processing system that integrates multiple logging tools and their measurements. The system acts as a mediator between the different logging methods (NMR, C/O, temperature) and the final saturation calculation, combining their strengths while compensating for their individual limitations to produce reliable saturation values across varying salinity conditions.
2Reliability
If carbon/oxygen logging is used to determine oil saturation, then the method can measure C/O ratio independent of water salinity, but existing techniques have relatively low logging speeds and lack desired accuracy
Solution Approach 1:
The patent merges NMR logging, C/O logging, and temperature logging into an integrated system. The NMR tool provides rapid porosity and saturation measurements, while the C/O tool provides carbon-oxygen ratio data independent of salinity. The temperature logging provides corrections for fluid properties. By combining these methods, the system achieves both high speed (from NMR) and high accuracy (from integrated analysis) simultaneously.
3Ease of manufacture
If constant average values of rock and fluid properties are used in saturation calculations, then the calculations are simplified, but the representation of oil saturation variations across the reservoir becomes coarse and lacks granular detail
Solution Approach 1:
The patent transitions from static constant average values to dynamic, depth-dependent property values. The system continuously calculates oil-carbon density at different depths using NMR viscosity data and temperature corrections, allowing the saturation calculation to adapt to changing rock and fluid properties along the wellbore. This dynamic approach provides granular, high-resolution saturation profiles while maintaining computational efficiency through automated continuous calculation.
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 provides an accurate and granular representation of oil saturation across the reservoir, improving the reliability of well logging and reservoir development decisions by accounting for variations in rock and fluid properties.
Implementation Method 1
NMR logging uses the NMR response to the hydrogen content of a reservoir to directly determine its porosity and estimate its permeability
Implementation Method 2
pulsed neutron (PN) logging operations typically measure gamma rays generated by absorption of neutrons produced by a neutron source in the surrounding reservoir
Implementation Method 3
A C/O logging tool may employ gamma ray spectroscopy measurements to directly sense the presence of carbon atoms in oil and oxygen atoms associated with water
Data Source
AI summary
Provided are techniques for saturation logging a hydrocarbon well in a hydrocarbon reservoir. The techniques including conducting a pulsed neutron (PN) logging of the well to generate a carbon/oxygen (C/O) log, conducting a nuclear magnetic resonance (NMR) logging of the well to generate a viscosity log, conducting a temperature logging of the well to generate a temperature log, determining a relationship of oil API gravity to viscosity and temperature for the reservoir, determining an oil API gravity log for the well based on the viscosity log, the temperature log, and the relationship of oil API gravity to viscosity and temperature, determining, based on the oil API gravity log, an oil density log for the well, determining, based on the oil density log, an oil-carbon density log for the well, and determining, based on the oil-carbon density log and the C/O log, a continuous oil saturation log for the well.