Gamma ray spectrum unfolding method for elemental capture spectroscopy logging and device therefor

Patent metadata

Field	Value
Publication number	US-11313223-B2
Application number	US-201816470539-A
Country	US
Kind code	B2
Filing date	Dec 10, 2018
Priority date	Dec 26, 2017
Publication date	Apr 26, 2022
Grant date	Apr 26, 2022

Abstract

A gamma ray spectrum unfolding method for elemental capture spectroscopy logging and a device therefor including the steps of first preprocessing the data obtained from an elemental capture spectrometry instrument; constructing a primary element group and an auxiliary element group according to the degree of interactions among the elements via theoretical analysis and numerical calculation of spectrum profiles, characteristic peak channels, and backgrounds of different elements; unfolding by using the least square method based on the construction of the primary element group and the auxiliary element group; and finally reconstructing the spectrum based on theory according to the yield of each element obtained by unfolding with the least square method, and comparing the measured gamma ray spectrum with the reconstructed gamma ray spectrum for error control, thereby improving the spectrum unfolding precision.

First claim

The invention claimed is:

1. A gamma ray spectrum unfolding method for elemental capture spectroscopy logging, comprising the following steps:
Step 1: acquiring and analyzing research area data at least including elemental capture gamma ray spectroscopy logging data and whole rock oxides analysis data, and determining the primary types of elements in the area;
Step 2: preprocessing the elemental capture gamma ray spectroscopy logging data, including selection of energy window, energy spectrum smoothing and filtering, normalization, and inelastic scattering information deduction, to obtain a preprocessed elemental capture gamma ray spectrum;
Step 3: constructing a primary element group and an auxiliary element group composed of different elements, to determine an order of spectrum unfolding for different elements;
Step 4: according to the primary element group and the auxiliary element group obtained in step 3, first unfolding the primary elements in the elemental capture gamma ray spectrum preprocessed in Step 2 by using the least square method, deducting the contribution of all the primary elements from the elemental capture gamma ray spectrum preprocessed in Step 2, and then unfolding the auxiliary elements by using the least square method, to obtain the relative yield of each element;
Step 5: according to the relative yield of each element obtained in Step 4, in combination with the normalized elemental capture standard gamma ray spectrum of single element, reconstructing the elemental capture gamma ray spectrum and comparing the reconstructed gamma ray spectrum with the measured gamma ray spectrum, to determine whether the unfolding results are reliable.

2. The unfolding method according to claim 1 , wherein, in Step 1, the acquired and analyzed research area data further include one or a combination of more of conventional logging data, logging data, and geological data; and the types of the primary elements in the research area are determined by: analyzing the whole rock oxides analysis data and optionally, one or a combination of more of conventional logging data, logging data, and geological data from the research area, determining the weight percentages of different kinds of oxides in the rock, and determining the primary types of elements in the area based on the weight percentage of each oxide.

3. The unfolding method according to claim 1 , wherein, in Step 2, the energy window selected ranges in channels 30-210.

4. The unfolding method according to claim 1 , wherein, in Step 2, the energy spectrum smoothing and filtering is carried out using a Savitzky-Golay filter and the Savitzky-Golay five-point filtering method by filtering the elemental capture gamma ray spectroscopy logging data in the range of the selected energy window, and the equation for the Savitzky-Golay five-point filtering method is shown in Equation 1 as below:

y
_

=

1
35

⁢

(

-
3

⁢

⁢

y

i
-
2

+

12
⁢

⁢

y

i
-
1

+

17
⁢

⁢

y
i

+

12
⁢

⁢

y

i
+
1

-

3
⁢

⁢

y

i
+
2

)

(

Equation
⁢

⁢
1

)

wherein, y represents a count at an address after filtering, y i represents a count at said address, y i−1 represents a count at the first address before said address, y i−2 represents a count at the second address before said address, y i+1 represents a count at the first address after said address, and y i+2 represents a count at the second address after said address.

5. The unfolding method according to claim 1 , wherein in Step 2, the normalization is carried out in a process where, with respect to the elemental capture gamma ray spectroscopy logging data having been subjected to energy window range selection and energy spectrum smoothing and filtering, the sum of the energy spectrum data of 181 channels is taken as 10 to provide a normalized elemental capture gamma ray spectrum by using the equation as shown in Equation 2 below:

N
Gkj

=

N
kj

∑

Assignees

• Petrochina Co Ltd

Inventors

• Wu Hongliang
• Li Ning
• Feng Zhou
• Lan Changlin
• Lv Tao
• Wang Kewen
• Feng Qingfu

Classifications

• E21B49/00 Primary

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• G01V5/101

  and detecting the secondary Y-rays produced in the surrounding layers of the bore hole · CPC title

• Y02A90/30

  Assessment of water resources · CPC title