NMR Oil Saturation Delimitation for In Natura Rock Samples
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Solution Overview
Problem
Existing methods for determining oil saturation in geological formations face challenges due to the non-uniqueness and noise in NMR data inversion, making it difficult to accurately classify fluid contents and quantify hydrocarbon saturation, especially when distinguishing between water and hydrocarbons.
Innovation Solution
A method that involves jointly processing NMR responses of oil and rock samples in situ, using a statistical inference scheme to delimit oil saturation by providing a range of admissible values based on minimal data requirements, without destructive sample manipulation, through discretization, preconditioning, normalization, and entropy maximization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If NMR response data is used to determine oil saturation, then measurement sensitivity to fluid contents is improved, but measurement precision is degraded due to non-uniqueness and noise in data inversion
Solution Approach 1:
The patent segments the NMR relaxation spectrum into multiple discrete components, each representing different fluid phases or pore size distributions. By decomposing the continuous relaxation spectrum into distinct segments with characteristic relaxation times, the method resolves the non-uniqueness problem in inversion while maintaining sensitivity to fluid contents. This segmentation allows separate characterization of oil and water signals that would otherwise be indistinguishable in the aggregate NMR response.
Solution Approach 2:
The patent applies dynamic optimization techniques to adjust inversion parameters and model assumptions based on the specific characteristics of each dataset. By dynamically adapting the inversion approach rather than using fixed parameters, the method achieves reliable and unique solutions across varying noise conditions and sample types, resolving the contradiction between measurement precision and solution uniqueness.
2Productivity
If traditional NMR inversion methods are used, then fluid content identification is attempted, but processing time and computational complexity increase due to extensive laboratory processes
Solution Approach 1:
The patent performs preliminary preprocessing of NMR data including noise filtering, baseline correction, and initial relaxation time estimation before the main inversion process. This preliminary action reduces the computational burden of the subsequent inversion by providing better initial conditions and reducing the search space, thereby decreasing overall processing time while maintaining accuracy.
Solution Approach 2:
The patent employs computationally efficient algorithms that use simplified models and approximations during initial processing stages, reserving more complex and time-consuming methods only when necessary. This approach uses 'cheap' computational methods for routine processing, significantly reducing laboratory processing time while maintaining sufficient accuracy for most applications.
3Measurement precision
If rock samples are manipulated extensively in laboratories, then measurement accuracy may be improved, but sample integrity is compromised and processing cost increases
Solution Approach 1:
The patent enables the NMR measurement process itself to provide all necessary information for accurate fluid saturation determination without requiring external sample manipulation or complementary laboratory tests. The method extracts multiple parameters (porosity, permeability, fluid saturation) directly from the NMR response, allowing the sample to 'serve itself' and eliminating procedures that would compromise sample integrity.
Solution Approach 2:
The patent measures multiple NMR relaxation parameters (T1, T2, diffusion coefficients) under different conditions to obtain comprehensive characterization of the sample. By changing measurement parameters rather than physically manipulating the sample, the method achieves high measurement precision while preserving sample integrity for potential future analysis.
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 a non-invasive, cost-effective, and time-efficient method to determine the range of oil saturation in rock samples, preserving sample integrity and reducing the need for extensive laboratory processes.
Implementation Method 1
the NMR response of the fluids of a formation stands out as one of the most relevant data for the identification, classification and quantification of its content. An NMR test, in any experimental context, is capable of separating and measuring the magnetization of the atomic nuclei present only in the fluids of a formation when it is subjected to magnetic fields.
Implementation Method 2
Nuclear spins exhibit a precession movement around the axis defined by the applied static magnetic field. Under a given static field magnitude, Bo, the frequency of this movement is an identifying attribute of the nuclear species, called the Larmor frequency, ω0.
Implementation Method 3
The application of a static field forces the nuclear spins, which are essentially magnetic dipoles, to align with the applied field. This process establishes the nuclear magnetization and has a characteristic time, denoted by T1, roughly speaking, associated with each molecular species that harbors spins of the probed nuclear species.
Data Source
AI summary
The present invention comprises a method for jointly processing data from the nuclear magnetic resonant (NMR) response of oil and rock samples in in natura condition, and its main product is the delimitation of the oil saturation (So) present in the rock samples, i.e., the determination of the range of admissible values of the volumetric fraction of the porous volume of the rock occupied by such fluid. The method requires a small volume of oil, originating from or of a composition similar to the oil present in the rock being tested, since it is based on both the measurement of the NMR response of the rock sample and the response of the fluid sample. These two sets of data feed a statistical inference scheme that (1) determines a range of admissible values for the So of the sample, delimited by the minimum and maximum oil saturation values compatible with the two sets of data presented; (2) produces, for each of these extreme values of admissible So, a decomposition of the rock relaxation time spectrum into two complementary spectra, the first highlighting the signatures relating to oil and the second comprising the distribution of the rock relaxometric signatures that cannot correspond to such fluid under the prescribed saturation condition.