Method and system of determining elemental content of an earth formation

Patent metadata

Field	Value
Publication number	US-9310514-B2
Application number	US-201013810975-A
Country	US
Kind code	B2
Filing date	Aug 24, 2010
Priority date	Aug 24, 2010
Publication date	Apr 12, 2016
Grant date	Apr 12, 2016

Abstract

Determining elemental content of an earth formation. At least some of the illustrative embodiments are methods including: irradiating a portion of a formation that surrounds a borehole; counting gammas to obtain a spectrum of counted gammas; finding a solution to a system of equations based on the spectrum of counted gammas, which system of equations has a plurality of solutions, the solution being indicative of a plurality of weight percentages for a respective plurality of elements within the formation; determining whether the solution meets a predetermined constraint; repeating the finding and determining until a solution is found that is determined to meet the predetermined constraint; and producing an indication of the elemental content of the formation using the solution that meets the predetermined constraint.

First claim

I claim:

1. A method comprising:
irradiating with neutrons a portion of a formation that surrounds a borehole with a source of neutrons from a tool positioned in the borehole;
counting gammas of different energy levels in response to the irradiation to obtain a spectrum of counted gammas with a gamma detector positioned in the borehole;
finding a solution to a system of equations based on the spectrum of counted gammas, which system of equations has a plurality of solutions, the solution being indicative of a plurality of weight percentages for a respective plurality of elements within the formation;
determining whether the solution meets a predetermined constraint on the relative weight percentages indicated for at least two of the elements within the formulation;
repeating the finding and determining until a solution is found that is determined to meet the predetermined constraint; and
outputting an indication of the elemental content of the formation using the solution that meets the predetermined constraint.

2. The method of claim 1 , wherein the predetermined constraint is determined from known weight percentages of the at least two elements in at least two minerals.

3. The method of claim 1 , wherein
determining further comprises determining whether the solution meets a further predetermined constraint on the relative weight percentages indicated for a third element, different from the at least two elements, and a fourth element, and
repeating further comprises repeating the finding and determining until a solution is found that is determined also to meet the further predetermined constraint.

4. The method of claim 3 , wherein the fourth element is the same element as one of the at least two elements.

5. The method of claim 1 , wherein the predetermined constraint relates the indicated weight percentage for at least one of the at least two elements to the weight percentages indicated for a plurality of the other elements within the formation.

6. The method of claim 1 , wherein the at least two elements include one or both of: magnesium; and aluminum.

7. The method of claim 1 , wherein irradiating further comprises irradiating with neutrons that, when departing the neutron source, have a mean energy of at least one selected from the group consisting of: about 4.5 Mega-electron Volts (MeV); and about 2.3 MeV.

8. The method of claim 1 , wherein irradiating further comprises irradiating with neutrons from a continuous source of neutrons.

9. The method of claim 1 , wherein irradiating further comprises irradiating the formation by way of a pulsed neutron source.

10. A system comprising:
a tool configured to be placed within a borehole in an earth formation, the tool comprising:
a source of neutrons; and
a gamma detector to detect gammas of different energy levels; and
a processor coupled to the gamma detector to:
find a solution to a system of equations based on the spectrum of counted gammas obtained by counting gammas of different energy levels detected at the gamma detector, the system of equations having a plurality of solutions, and the solution being indicative of a plurality of weight percentages for a respective plurality of elements within the formation;
determine whether the solution meets a predetermined constraint on the relative weight percentages indicated for at least two of the elements; and
if the solution does not meet the predetermined constraint, discard the solution and repeat the processes to find a different solution to the system of equations until a solution is found which is determined to meet the predetermined constraint.

11. The system of claim 10 , wherein the predetermined constraint is determined from known weight percentages of the at least two elements in at least two minerals.

12. The system of claim 10 , wherein when the processor is further to:
determine whether the solution meets a further predetermined constraint on the relative weight percentages indicated for a third element, different from the at least two elements, and a fourth element; and,
if the solution does not meet the further predetermined constraint, discard the solution and repeat the processes to find a different solution to the system of equations until a solution is found which is determined to meet both predetermined constraints.

13. The system of claim 10 , wherein the predetermined constraint relates the weight percentage indicated for at least one of the at least two elements to the weight percentages indicated for a plurality of the other elements within the formation.

14. The system of claim 10 , wherein the at least two elements include one or both of: magnesium; and aluminum.

15. The system of claim 10 , wherein the source of neutrons is to produce neutrons that have a mean energy of at least one selected from the group consisting of: about 4.5 Mega-electron Volts (MeV); and about 2.3 MeV.

16. The system of claim 10 , wherein the source of neutrons is a continuous source of neutrons.

17. The system of claim 10 , wherein the source of neutrons is a pulsed source.

18. The system of claim 10 , wherein the tool includes a wireline logging pressure vessel, with the neutron source and gamma detector disposed within the pressure vessel.

19. The system of claim 10 , wherein the tool is or can be coupled within a drill string.

20. A non-transitory computer-readable medium storing a program that, when executed by a processor, causes the processor to:
find a solution to a system of equations based on a spectrum of counted gammas received from a gamma detector of a tool positioned in a borehole of a formulation, which system of equations has a plurality of solutions, the solution being indicative of a plurality of weight percentages for a respective plurality of elements within formation;
determine whether the solution meets a predetermined constraint on the relative weight percentages indicated for at least two of the elements with the formulation; and
if the solution does not meet the predetermined constraint, discard the solution and repeat the processes to find a different solution to the system of equations until a solution is found which is determined to meet the predetermined constraint.

21. The non-transitory computer-readable medium of claim 20 , wherein the predetermined constraint is determined from known weight percentages of the at least two elements in at least two minerals.

22. The non-transitory computer-readable medium of claim 20 , wherein, when executed by a processor, the program further causes the processor to:
determine whether the solution meets a further predetermined constraint on the relative weight percentages indicated for a third element, different from the at least two elements, and a fourth element; and,
if the solution does not meet the further predetermined constraint, discard the solution and repeat the processes to find a different solution to the system of equations until a solution is found which is determined to meet both predetermined constraints.

23. The non-transitory computer-readable medium of claim 20 , wherein the predetermined constraint relates the weight percentage indicated for at least one of the at least two elements to the weight percentages indicated for a plurality of the other elements within the formation.

Assignees

• Galford James E
• Halliburton Energy Services Inc

Inventors

• Galford James E

Classifications

• G01V5/101 Primary

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