Method of determining solid and liquid components in sedimentary rocks using NMR relaxation
Inventors
SINGER, PHILIP M. • Liu, Yunke • Wang, Xinglin • Hirasaki, George J. • Vinegar, Harold J.
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Assignees
Vinegar Technologies LLC • William Marsh Rice University
Member
Rice UniversityRice University is a leading research university in Houston, Texas, recognized for its emphasis on scientific discovery, innovation, and interdisciplinary collaboration. The institution is committed to academic excellence, impactful research, and community engagement, offering robust undergraduate and graduate programs in engineering, natural sciences, social sciences, humanities, business, and the arts. Rice is distinguished by its history of collaboration with organizations such as NASA, fostering advances in space science, biotechnology, energy research, and artificial intelligence.
Rice University is a leading research university in Houston, Texas, recognized for its emphasis on scientific discovery, innovation, and interdisciplinary collaboration. The institution is committed to academic excellence, impactful research, and community engagement, offering robust undergraduate and graduate programs in engineering, natural sciences, social sciences, humanities, business, and the arts. Rice is distinguished by its history of collaboration with organizations such as NASA, fostering advances in space science, biotechnology, energy research, and artificial intelligence.
Publication Number
US-12228531-B1
Publication Date
2025-02-18
Expiration Date
Abstract
A method for separating liquid-like (T2e) from solid-like (T2G) 1H NMR transverse relaxation times in porous media uses novel pulse sequences together with a 1H NMR spectrometer optimized for geological core samples. The method is applied to obtain 1D T2 distributions and 2D T1-T2 maps in organic-rich chalks for quantification of liquid-like signal (micropore fluids, meso-macropore fluids, fluids dissolved in organic matter, and clay-bound water) and solid-like signal (kerogen, bitumen, and clay hydroxyls). The novel pulse sequences comprise a solid-echo, which detects more solid-like signal than an FID. The method is used for fluid typing in micro/meso-macro pores, clay mineral identification, determination of kerogen content, and quantification of solvent-extracted bitumen versus bitumen expelled from kerogen due to swelling from dissolved hydrocarbons. The method is used to quantify the asphaltene, resin, aromatic, and/or saturate content of bitumen in the rock.
Core Innovation
A novel 1H NMR method is disclosed for separating liquid-like (T2e) from solid-like (T2G / T*2G) transverse relaxation components in porous geological media using novel pulse sequences together with a 1H NMR spectrometer optimized for geological core samples. The method acquires liquid-like components with an inversion-recovery CPMG measurement and acquires solid-like components using an inversion-recovery solid-echo measurement with minimal instrumental deadtime, processes the respective measurements via inverse Laplace techniques (multi-exponential for liquid-like and multi-Gaussian for solid-like), and splices the resulting distributions to produce 1D P(T*2G; T2e) distributions and 2D P(T1,{T*2G; T2e}) maps for characterizing samples, including determining structure and plurality of components.
The invention addresses the problem that currently there is no reliable method to interpret the 1H NMR T2 relaxation of porous geological media containing both liquid-like and solid-like components without losing information about one of the components. The background identifies complications arising from the coexistence of multi-exponential (T2e) and multi-Gaussian (T2G) decays, dephasing in inhomogeneous magnetic fields, instrumental deadtime limitations, and limitations of prior inversion approaches which introduce additional parameters or are not adapted to T1-T2 mapping.
Claims Coverage
Two independent claims were identified and eight main inventive features were extracted from the patent claims.
Inversion-recovery solid-echo sequence for T1-T*2G mapping
An inversion-recovery solid-echo measurement where longitudinal magnetization is inverted or saturated and subsequently converted to transverse magnetization with a solid-echo to produce solid-like transverse relaxation data, which is processed to produce a T1-T*2G map for characterizing the sample (structure and plurality of components).
Sampling solid-echo magnetization to obtain T*2G
Sampling the observable solid-echo magnetization with discretized time steps during decay to acquire signal amplitude measurements characterized by a decay time constant T*2G, used in processing to determine solid-like relaxation distributions.
Repeating measurements with different recovery times for T1 encoding
Repeating the inversion-recovery solid-echo measurements responsively to recovery of the sample substantially to equilibrium with different selected recovery times τ1 to provide T1 encoding for generation of the T1-T*2G map.
Measuring liquid-like components using inversion-recovery CPMG without dephasing
Acquiring liquid-like components with an inversion-recovery CPMG sequence designed to measure liquid-like multi-exponential T2e components without dephasing from the inhomogeneous magnetic field, producing data for T1-T2e mapping.
Processing liquid-like data to produce T1-T2e maps
Processing inversion-recovery CPMG measurements of liquid-like components using multi-exponential inverse Laplace techniques to produce T1-T2e maps of the liquid-like components.
Measuring solid-like components with minimal instrumental deadtime
Measuring solid-like components using an inversion-recovery solid-echo sequence with minimal instrumental deadtime (specified as not greater than 0.01 ms in embodiments) to capture solid-like multi-Gaussian T*2G components.
Processing solid-like data to produce T1-T*2G maps
Processing inversion-recovery solid-echo measurements using multi-Gaussian (or sinc-Gaussian) inversion kernels to produce T1-T*2G maps of the solid-like components, with longitudinal recovery inverted using an exponential kernel.
Splicing T1-T2e and T1-T*2G maps using a T2 cutoff
Combining the T1-T2e map with the T1-T*2G map using a T2 cutoff (distinction between solid-like and liquid-like by transverse relaxation time or viscosity) to create a spliced T1-{T*2G; T2e} map, and analyzing the spliced map for characterizing the sample, including determining structure and plurality of components.
The independent claims center on complementary acquisition and processing of inversion-recovery CPMG (liquid-like) and inversion-recovery solid-echo (solid-like) measurements, the production of respective T1-T2e and T1-T*2G maps, and the splicing of those maps via a T2 cutoff to yield a combined T1-{T*2G; T2e} map for sample characterization.
Stated Advantages
Captures liquid-like T2e components without dephasing from the inhomogeneous magnetic field and captures solid-like T*2G components with minimal deadtime, thereby avoiding loss of information about one component.
Performs liquid-solid decomposition with a minimal number of additional free parameters compared to prior methods that introduce extra inversion parameters.
Is easily adaptable to T1-T2 mapping, enabling 2D P(T1,{T*2G; T2e}) maps for improved fluid typing and saturation interpretation in organic-rich cores.
The solid-echo detects more solid-like signal than an FID (approximately 15% more signal in embodiments) and allows a greater data-sampling rate compared to solid-echo train approaches, improving inversion stability for solid-like components.
Enables quantitative characterization including clay-mineral identification, determination of kerogen content, quantification of solvent-extracted versus expelled bitumen, and quantification of SARA (asphaltene, resin, aromatic, saturate) fractions and other NMR-derived geochemical quantities.
Documented Applications
Obtaining 1D T2 distributions and 2D T1-T2 (T1-{T*2G; T2e}) maps in organic-rich chalks for quantification of liquid-like signal (micropore fluids, meso-macropore fluids, fluids dissolved in organic matter, and clay-bound water) and solid-like signal (kerogen, bitumen, and clay hydroxyls).
Fluid typing in micro/meso-macro pores and improved fluid saturation interpretation in organic-rich chalk and shale using T1/T2 contrasts between water and light hydrocarbons.
Clay mineral identification and quantification of clay hydroxyl signal (e.g., kaolinite interpretation) using T1-T*2G maps.
Determination and quantification of kerogen content and separation of kerogen versus bitumen signals in core samples.
Quantification of solvent-extracted bitumen versus bitumen expelled from kerogen due to swelling from dissolved hydrocarbons, and use of bitumen measurements to infer SARA (asphaltene, resin, aromatic, saturate) composition.
Prediction of NMR-derived geochemical quantities including S1, S2, S1/S2, HI, OI, and elemental ratios H/C, H/S, H/O, H/N for crude-oil or bitumen, and application to bulk crude-oil or bulk bitumen to predict SARA fractions.
Demonstration on organic-rich chalk core samples from a natural gas liquids reservoir for petrophysical and geochemical characterization.
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