Method of estimating permeability using NMR diffusion measurements
Inventors
Vinegar, Harold J. • SINGER, PHILIP M. • Hirasaki, George J. • CHEN, Zeliang • Wang, Xinglin • Vinegar, Eva
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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-11933932-B1
Publication Date
2024-03-19
Expiration Date
Abstract
This invention is useful for determining the permeability of a geological formation using 1H NMR diffusion measurements acquired in the laboratory and using downhole 1H NMR well logging. The current technology for obtaining formation permeability downhole using NMR is not adequate for low-permeability, unconventional source rock formations with high organic content. This new method uses laboratory 1H NMR diffusion measurements for creating continuous downhole well logs of the mobile-hydrocarbon permeability of the hydrocarbon-filled pore space of downhole geological formations.
Core Innovation
This is a new method for estimating the permeability (k) of an oil or gas formation using NMR restricted diffusion and relaxation data. The method determines pore-body size (d) from surface-to-volume ratio and tortuosity (τ) from restricted diffusion measurements, and uses these, together with porosity (ϕ) and an estimate of pore-body-to-pore-throat ratio (BTR) for known lithologies, in a Carman-Kozeny–based equation to predict the permeability of the mobile hydrocarbons in the hydrocarbon-filled pore space. [procedural detail omitted for safety]
The invention addresses the problem that conventional techniques for obtaining downhole permeability using NMR are not adequate for low-permeability, unconventional source rock formations with high organic content, and that conventional methods become less accurate at lower permeabilities leading to unacceptable reliance on dense coring. The background states there is an ongoing need for novel techniques which accurately measure downhole permeability with a minimum reliance on core sampling.
The method applies a Padé fit to restricted-diffusivity versus diffusion-length data to estimate tortuosity and pore-body size, uses those parameters (with porosity and an assumed or measured BTR) in a modified Carman-Kozeny permeability relation, and is intended for both laboratory NMR core analysis and downhole gradient-based NMR logging to produce continuous downhole logs of mobile-hydrocarbon permeability. [procedural detail omitted for safety]
Claims Coverage
The independent claims disclose 3 sets of inventive features. The main inventive features concern (1) a laboratory-and-log workflow to map subsurface permeability using core-derived BTR and tortuosity, (2) an NMR restricted-diffusion method on cores with connate water to estimate tortuosity and surface-to-volume and then compute mobile-hydrocarbon permeability, and (3) a lab-calibrated workflow using D-T2 core measurements and Padé fits to produce downhole permeability logs.
Core-set acquisition from extraction locations
Acquiring a set CORE_SET of N core samples where each core-sample is extracted from a respective downhole extraction-location EXTRACTION-LOC(CSi).
Lab NMR measurement of movable hydrocarbon porosity
For each core sample, performing a lab-NMR measurement of a respective porosity ϕM(CSi) describing the porosity of movable hydrocarbons.
Lab measurement of pore-dimension properties
For each core sample, performing a lab-NMR measurement of one or more pore-dimension properties (e.g., surface-to-volume ratio or pore diameter as recited in dependent claims).
Laboratory permeability measurement
For each core sample, performing a respective laboratory measurement of the permeability k(CSi) of the core sample.
Estimating downhole hydraulic tortuosity
For each core sample, estimating a respective downhole hydraulic tortuosity τhy(EXTRACTION-LOC(CSi)) representing the downhole tortuosity at the extraction-location from which the core was extracted.
Computing a one-dimensional BTR-map
Computing, from the results of the laboratory measurements and tortuosity estimates, an at least 1-D BTR-map of subsurface body-throat ratio (BTR) as a function of subsurface location.
Downhole NMR logging of porosity and pore-size parameter
For a plurality of downhole locations, downhole-NMR-logging the subsurface porosity and a subsurface pore-size parameter.
Computing a subsurface permeability map from core and log data
Computing an at least 1-D map of subsurface permeability as a function of downhole-location from the BTR-map, the results of the downhole-NMR-logging, and the tortuosity estimates.
NMR restricted-diffusion on cores with connate water
Performing NMR restricted diffusion measurements on a core with connate water present to obtain restricted diffusivity of multiple hydrocarbons, with step (a) procedural details omitted. [procedural detail omitted for safety]
Estimating tortuosity and surface-to-volume from restricted diffusivity
Measuring NMR restricted diffusion of two hydrocarbons in the hydrocarbon-bearing porosity and estimating the tortuosity and surface-to-volume ratio of the hydrocarbon-filled pore space from the restricted-diffusivity data (e.g., via a Padé fit as recited in dependent claims).
Permeability of mobile hydrocarbons from NMR-derived parameters
Using the tortuosity, surface-to-volume ratio, and porosity occupied by the hydrocarbon fluids, together with an estimate of the pore body-to-pore-throat ratio for the lithology, to determine the permeability of the mobile hydrocarbons in the core (the claims recite a permeability equation k=ϕ d2/3 2 τ BTR2 or equivalent forms).
Padé fitting D/D0 versus LD to obtain d, LM and τ
Fitting restricted diffusion (D/D0) versus diffusion length (LD) using a Padé fit to determine pore body size (d), heterogeneity length scale (LM), and tortuosity (τ) for each core.
Determining cementation exponent from tortuosity and movable porosity
Determining the cementation exponent m for each lithology using the relationship τ=ϕM1-m (i.e., relating tortuosity to movable-fluid porosity).
Determining BTR from Carman-Kozeny and core permeability
Measuring core permeability and determining the body-throat ratio BTR for each lithology from a Carman-Kozeny relationship (k=ϕM d2/3 2 τ BTR2 or modified forms).
Generating downhole permeability logs using core-calibrated parameters
Using core-calibrated parameters (including BTR and m) with D-T2 downhole logs to determine downhole permeability klog by measuring D-T2 logs, computing τlog from ϕM,log and m, fitting Dlog/D0 versus T2 with fixed LM to obtain dlog, and computing klog=ϕM,log dlog2/3 2 τlog BTR2.
The independent claims disclose a combined laboratory and downhole workflow that uses lab NMR measurements (movable-hydrocarbon porosity, pore-dimension properties, permeability), tortuosity estimation, computation of a BTR map, Padé fitting of restricted-diffusion data to obtain d, LM and τ, and application of a (modified) Carman-Kozeny permeability relation to produce continuous downhole permeability logs for mobile hydrocarbons.
Stated Advantages
Useful for determining the permeability of a geological formation using 1H NMR diffusion measurements acquired in the laboratory and using downhole 1H NMR well logging.
Creates continuous downhole well logs of the mobile-hydrocarbon permeability of the hydrocarbon-filled pore space of downhole geological formations.
Improves logistics, robustness and accuracy compared to the previously published method.
Delivers good permeability estimation without empirical parameters for both low-permeability organic-rich chalks and conventional formations such as Austin chalk and Indiana limestone.
Documented Applications
Determining the mobile-hydrocarbon permeability (kX) of core samples for NMR core analysis.
Generating continuous downhole permeability logs of mobile-hydrocarbon permeability using gradient-based NMR logging tools.
Using the downhole permeability map to inform decisions such as drilling one or more horizontal or vertical wells, casing and perforating, and deploying a pump, as recited in the claims.
Applying the method to low-permeability, unconventional organic-rich chalks and to conventional carbonate and limestone formations for permeability estimation.
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