Determining mineralogy of an earth formation using linear regressions

Patent metadata

Field	Value
Publication number	US-9874551-B2
Application number	US-201414211751-A
Country	US
Kind code	B2
Filing date	Mar 14, 2014
Priority date	Mar 14, 2014
Publication date	Jan 23, 2018
Grant date	Jan 23, 2018

Abstract

A method for determining mineralogy of a formation includes determining a model of arenites in the formation by performing a first type of linear regression on a plurality of elemental dry weights of the formation based upon a sum of elemental dry weights of calcium and magnesium being at least a given value, or performing a second type of linear regression on the elemental dry weights based upon the sum of the elemental dry weights of elemental calcium and magnesium being less than the given value. A model of arkoses in the formation is determined by performing a third type of linear regression on the elemental dry weights. A partitioning function is then determined. The mineralogy of the formation is then determined by applying the partitioning function to the model of arenites and the model of arkoses, and adding the model of arenites and the model of arkoses together.

First claim

The invention claimed is:

1. A method for determining mineralogy of rock comprising:
lowering an elemental spectroscopy logging tool into a borehole penetrating the rock;
irradiating the rock with neutrons emitted by the elemental spectroscopy logging tool;
measuring gamma rays from the rock resulted from said irradiating;
determining a model of arenites in the rock by using a processor to
perform a first type of linear regression on a plurality of elemental dry weights of the rock based upon a sum of elemental dry weights of calcium and magnesium being at least a given value, or
perform a second type of linear regression on the plurality of elemental dry weights based upon the sum of the elemental dry weights of elemental calcium and magnesium being less than the given value;

determining a model of arkoses in the rock, by performing a third type of linear regression on the plurality of elemental dry weights, using the processor;
determining a partitioning function, using the processor; and
determining the mineralogy of the rock by using the processor to
apply the partitioning function to the model of arenites and the model of arkoses, and
add the model of arenites and the model of arkoses together to create a combined model;

using the determined mineralogy of the rock in a drilling, simulation, or completion, operation on the wellbore penetrating the rock.

2. The method of claim 1 , wherein the given value is a carbonate point.

3. The method of claim 1 , wherein the sum of the elemental dry weights of calcium and magnesium being less than the given value indicates an amount of carbonates in the rock being less than an amount of carbonates in the rock if the sum of the calcium and magnesium elemental dry weights had been at least the given value.

4. The method of claim 1 , wherein the partitioning function is based upon at least one elemental dry weight and/or a priori knowledge.

5. The method of claim 1 , wherein the partitioning function is based upon elemental dry weights of potassium and/or sodium.

6. The method of claim 1 , wherein the models of arenites and arkoses are determined at a plurality of depth levels in the rock.

7. The method of claim 6 , wherein the partitioning function used for the models of arenites and arkoses at a given depth level is based upon averages of potassium and/or sodium elemental dry weights over at least some of the plurality of depth levels.

8. The method of claim 6 , wherein the partitioning function used for the models of arenites and arkoses at a given depth level is based upon averages of potassium and/or sodium elemental dry weights over an interval of the plurality of depth levels containing the given depth level.

9. The method of claim 1 , wherein the determined mineralogy of the rock includes at least one of the group consisting of quartz, albite, anorthite, orthoclase, kaolinite, illite, smectite, chlorite, muscovite, biotite, calcite, dolomite, siderite, ankerite, pyrite, anhydrite, salt, and coal.

10. The method of claim 1 , further comprising reducing a value of at least one elemental dry weight to a corresponding maximum value, based upon at least one other elemental dry weight, prior to performing the first type of linear regression.

11. The method of claim 1 , further comprising reducing a value of at least one mineral in the determined mineralogy of the rock to a corresponding maximum value, based upon at least one elemental dry weight.

12. The method of claim 1 , further comprising reducing a value of an elemental dry weight of potassium to a maximum potassium value, based upon an elemental dry weight of aluminum, prior to performing the first type of linear regression.

13. The method of claim 1 , further comprising adding at least one mineral having a fixed elemental composition to the combined model; and further comprising normalizing the combined model such that a sum of concentrations of the at least one mineral having the fixed elemental composition and concentrations of minerals in the determined model is 100%.

14. The method of claim 13 , wherein the at least one mineral having a fixed elemental composition includes at least one of the group consisting of pyrite, anhydrite, coal, and salt.

15. The method of claim 13 , further comprising reducing at least one mineral in the combined model to a corresponding maximum value, based upon at least one other mineral in the combined model having a fixed elemental composition.

16. The method of claim 15 , wherein the at least one other mineral having a fixed elemental composition includes at least one of the group consisting of quartz, calcite, dolomite, and siderite.

17. The method of claim 15 , further comprising re-normalizing the combined model to account for the reduction of the at least one mineral in the combined model to the corresponding maximum value.

18. The method of claim 17 , further comprising performing a quality check by computing a plurality of elemental dry weights of constituent elements of the model, and comparing the computed plurality of elemental dry weights of constituent elements of the model to the plurality of elemental dry weights of the rock.

Assignees

• Schlumberger Technology Corp

Inventors

• Herron Susan
• Herron Michael
• May Dale

Classifications

• G01N33/24 Primary

  Earth materials (G01N33/42 takes precedence) · CPC title

• G01V5/10

  using neutron sources {(neutron generating tubes H05H5/00; neutron sources using isotopes G21G4/00)} · CPC title

• E21B49/00

  Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells · CPC title