Analyzing fluids in core samples contained in pressurized NMR core holders with 1H and 19F NMR
Pressure coring where the core apparatus drills the core sample and seals the core sample at its native downhole pressure (e.g., several thousand psi) may be expanded to include nuclear magnetic resonance (NMR) imaging components to produce a pressurized NMR core holder that allows for NMR imaging of the core samples having been maintained in a downhole fluid saturation state. NMR imaging performed may include 1H and also 19F imaging depending on the chamber fluid used in the pressurized NMR core holder.
1. A method comprising:
collecting one or more core samples from a subterranean formation with a coring tool coupled to a pressurized nuclear magnetic resonance (NMR) core holder;
placing the one or more core samples in the pressurized NMR core holder comprising one or more NMR coils and containing a fluid;
retrieving the pressurized NMR core holder from the subterranean formation where the one or more core samples are at a downhole fluid saturation state;
performing 1H NMR measurements on at least one of the one or more core samples in the pressurized NMR core holder at the downhole fluid saturation state; and
deriving one or more properties of the at least one of the one or more core samples based on the 1H NMR measurements.
2. The method of claim 1 , wherein the fluid comprises one or more selected from the group consisting of a viscosifier and a weighting agent.
3. The method of claim 1 , wherein the one or more properties of the at least one of the one or more core samples is selected from the group consisting of porosity, movable and non-movable fluids, hydrocarbon fluid types and saturation, wettability, organic content, pore structure including pore size distribution, permeability, and fracture and pore connectivity.
4. The method of claim 1 , wherein the fluid is a hydrogen-absent fluid.
5. The method of claim 1 , wherein the fluid comprises a fluorine-containing fluid and the method further comprises:
performing 19F NMR measurements on the at least one of the one or more core samples at the downhole fluid saturation state; and
deriving the one or more properties of the at least one of the one or more core samples based on the 1H NMR measurements and the 19F NMR measurements.
6. The method of claim 5 , wherein deriving the one or more properties of the at least one of the one or more core samples comprises:
producing a 1H image of the 1H NMR measurements;
producing a 19F image of the 19F NMR measurements; and
comparing the 1H image and the 19F image to derive where the fluorine-containing fluid has infiltrated the at least one of the one or more core samples.
7. The method of claim 5 , wherein deriving the one or more properties of the at least one of the one or more core samples comprises:
calibrating the 1H NMR measurements to a 1H NMR measurement of water to produce calibrated 1H NMR measurements;
calibrating the 19F NMR measurements to a 19F NMR measurement of the fluorine-containing fluid to produce calibrated 19F NMR measurements;
producing a calibrated 1H image of the calibrated 1H NMR measurements; and
producing a calibrated 19F image of the calibrated 19F NMR measurements.
8. The method of claim 7 , wherein deriving the one or more properties of the at least one of the one or more core samples further comprises:
summing the calibrated 1H image and the calibrated 19F image; and
deriving porosity of the at least one of the one or more core samples therefrom.
9. The method of claim 7 , wherein deriving the one or more properties of the at least one of the one or more core samples further comprises:
ensemble averaging data points of the calibrated 1H image and data points of the calibrated 19F image; and
deriving porosity of the at least one of the one or more core samples therefrom.
10. The method of claim 7 , wherein deriving the one or more properties of the at least one of the one or more core samples further comprises:
subtracting data points of the calibrated 19F image having a value within 20% of a value of the fluorine-containing fluid to yield an infiltration image.
11. The method of claim 7 , wherein deriving the one or more properties of the at least one of the one or more core samples further comprises:
subtracting data points of the calibrated 19F image having a value at least 20% greater than or at least 20% less than of a value of the fluorine-containing fluid to yield a boundary image where a negative space of the boundary image is an adjusted core volume; and
deriving the one or more properties of the at least one of the one or more core samples based on the 1H NMR measurements and/or the 19F NMR measurements that fall within the adjusted core volume.
12. The method of claim 11 , wherein the subterranean formation comprises a carbonate lithology.
13. The method of claim 1 , wherein the fluid comprises a perfluorohydrocarbon and a perfluoropolymer.
14. The method of claim 1 , wherein the 1H NMR measurements are first 1H NMR measurements and the method further comprises:
reducing a fluid pressure in the pressurized NMR core holder to a reduced fluid pressure; and
performing second 1H NMR measurements on the at least one of the one or more core samples in the pressurized NMR core holder at the downhole fluid saturation state.