Nuclear magnetic resonance rock sample analysis method and instrument with constant gradient field

Patent metadata

Field	Value
Publication number	US-9625601-B2
Application number	US-201114344285-A
Country	US
Kind code	B2
Filing date	Sep 28, 2011
Priority date	Sep 14, 2011
Publication date	Apr 18, 2017
Grant date	Apr 18, 2017

Abstract

The present invention relates to a constant gradient field nuclear magnetic resonance (NMR) rock sample analysis method and instrument. The method includes: in a constant gradient magnetic field, performing NMR measurement to acquire data; converting the measured NMR data into a two-dimensional NMR spectrum D-T 2 ; performing measurement and inversion on a standard sample of a constant gradient field to obtain a standard sample two-dimensional NMR spectrum D-T 2 ; measuring the sample to acquire a two-dimensional NMR spectrum D-T 2 of a fluid in the sample; identifying fluid types according to the practically measured two-dimensional NMR spectrum D-T 2 ; computing the fluid property and the petrophysical parameters according to the two-dimensional NMR spectrum D-T 2 of the fluid in the sample; performing single slice scanning on the sample to acquire partial oil and water saturation; performing continuous slice scanning to obtain axial oil and water saturation distribution and movable fluid saturation distribution of the sample.

First claim

What is claimed is:

1. A constant gradient field nuclear magnetic resonance (NMR) rock sample analysis method, characterized in that it comprises:
1) in a constant gradient field generated by a magnet, according to a saturated fluid in a sample under test, designing parameters comprising an echo train k, a pulse interval tau, the number of 180° pulses Ne, and a waiting time RD in a CGMF-CPMG pulse sequence to perform NMR measurement to acquire measurement data; the value of k is between 2 and 8, the value of tau is distributed between 150 μs and 20000 μs, the value of Ne is distributed between 128 and 30720, and the waiting time is distributed between 2000 ms and 12000 ms;
2) converting NMR data measured in Step 1) into a two-dimensional NMR spectrum D-T 2 ; the data measured by adopting the CGMF-CPMG pulse sequence conforms to a multiexponential attenuation rule:

b
ik

=

∑

j
=
1

m

⁢

∑

l
=
1

p

⁢

f
lj

⁢

exp
⁡

(

-

1
12

⁢

γ
2

⁢

g
2

⁢

tau
k
2

⁢

D
l

⁢

t
i

)

⁢

exp
⁡

(

t
i

/

T

2
⁢
j

)

+

ɛ
ik

(
5
)

wherein: i=1, . . . , n k , k=1, . . . , q, l=1, p, and j=1, . . . , m;
i denotes the ith echo of the kth echo train, dimensionless;
k denotes the kth echo train, dimensionless;
l denotes the lth diffusion coefficient selected in advance, dimensionless;
j denotes the jth relaxation time selected in advance, dimensionless;
n k is the number of echoes of the kth echo train, dimensionless;
q is the number of echo trains of different tau k , dimensionless;
p denotes the number of diffusion coefficients selected in advance;
m denotes the number of relaxation times selected in advance;
b ik denotes the amplitude of the ith echo of the kth echo train with the pulse interval being tau k , dimensionless;
f ij denotes the amplitude when the diffusion coefficient is D l , and the relaxation time is T 2 j , dimensionless;
γ is the gyromagnetic ratio, unit: MHz/T;
G is the magnetic field gradient, unit: Gauss/cm;
tau k , is the pulse interval of the kth echo train, unit: us;
and performing inversion on Equation (5) by adopting an improved singular value de composition method to acquire the two-dimensional NMR spectrum D-T 2 ;

3) performing measurement and inversion on a constant gradient field standard sample using Step 1) and Step 2) to obtain the two-dimensional NMR spectrum D-T 2 of the standard sample; taking 12 constant gradient field NMR standard samples, porosities being 0.5%, 1%, 2%, 3%, 6%, 9%, 12%, 15%, 18%, 21%, 24%, and 27%, respectively, for each time of calibration, select at least 5 of the 12 for measurement and inversion to obtain two-dimensional NMR spectra of standard samples with different porosities, then performing volume integration on the two-dimensional NMR spectra to obtain NMR signals of the standard samples; the ratio between the NMR signal and the volume of the standard sample being the NMR signal of a unit volume; and performing linear fitting on porosity and the NMR signal of the unit volume to obtain a relationship line thereof:
y=ax+b   (8)

wherein y represents the NMR signal quantity of a unit volume, x represents an NMR porosity (%), a represents a slope, and b represents a Y-intercept;
when measuring the rock sample, measuring the NMR signal of a unit volume of the rock sample to compute the porosity of a rock sample;

4) measuring the rock sample using Step 1) and Step 2), acquiring a fluid two-dimensional NMR spectrum D-T 2 in the rock sample, performing fluid types identification according to a practically measured two-dimensional NMR spectrum D-T 2 of the rock sample; wherein the diffusion coefficient of water is a constant, and is related to the temperature; the diffusion coefficient of gas is related to the temperature and pressure; and a linear relationship exists between the diffusion coefficient and relaxation time of crude oil;
D w ( T 2 )= D w ( T )  (

Assignees

• Liu Wei
• Sun Wei
• Gu Zhaobin
• Sun Dianqing
• Petrochina Co Ltd

Inventors

• Liu Wei
• Sun Wei
• Gu Zhaobin
• Sun Dianqing

Classifications

• G01R33/4835

  of multiple slices · CPC title

• G01R33/383

  using permanent magnets · CPC title

• G01R33/3806

  Open magnet assemblies for improved access to the sample, e.g. C-type or U-type magnets · CPC title

• G01R33/445

  MR involving a non-standard magnetic field B0, e.g. of low magnitude as in the earth's magnetic field or in nanoTesla spectroscopy, comprising a polarizing magnetic field for pre-polarisation, B0 with a temporal variation of its magnitude or direction such as field cycling of B0 or rotation of the direction of B0, or spatially inhomogeneous B0 like in fringe-field MR or in stray-field imaging · CPC title

• G01V3/14 Primary

  operating with electron or nuclear magnetic resonance · CPC title