Methods for evaluating cuttings density while drilling

Patent metadata

Field	Value
Publication number	US-9228430-B2
Application number	US-201213585562-A
Country	US
Kind code	B2
Filing date	Aug 14, 2012
Priority date	Aug 26, 2011
Publication date	Jan 5, 2016
Grant date	Jan 5, 2016

Abstract

A method evaluating a cuttings density while drilling a subterranean wellbore includes acquiring first and second axially spaced pressure measurements in the wellbore. The pressure measurements may then be processed to obtain an interval density of drilling fluid between the measurement locations. A tool string including a large number of axially spaced pressure sensors (e.g., four or more or even six or more) electronically coupled with a surface processor via wired drill pipe may be used to obtain a plurality of interval densities corresponding to various wellbore intervals. The interval density may be measured while drilling and may be further processed to compute a cuttings density in the annulus. Moreover, changes in the computed interval density with time while drilling may be used as an indicator of a change in cuttings density.

First claim

What is claimed is:

1. A method for identifying a change in cuttings density while drilling, the method comprising:
(a) rotating a drill bit in a subterranean wellbore, the drill bit being deployed in a drill string including first and second axially spaced along string pressure sensors, said rotating operative to drill the wellbore and produce formation cuttings which are transported to a surface location via circulating drilling fluid in a wellbore annulus;
(b) using the first and second along string pressure sensors to make first and second subsurface annular pressure measurements while drilling in (a);
(c) transmitting the annular pressure measurements to a processor;
(d) processing the annular pressure measurements to compute an annular interval density of the circulating drilling fluid while drilling in (a);
(e) repeating (b), (c), and (d) and monitoring the computed annular interval densities with time while drilling in (a); and
(f) evaluating a change in the annular interval densities computed in (d) as an indicator of a change in a density of the formation cuttings.

2. The method according to claim 1 , wherein:
(d) further comprises processing the annular pressure measurements in combination with an annular friction component to compute a plurality of measured annular interval static densities of the drilling fluid while drilling in (a);
(e) further comprises monitoring the measured annular interval static densities with time while drilling in (a); and
(f) further comprises evaluating a change in at least one of the measured annular interval static densities as an indicator of a change in the density of the formation cuttings.

3. The method according to claim 2 , wherein (f) further comprises evaluating a change in a lowermost one of the computed annular interval static densities as an indicator of a change in the density of the formation cuttings.

4. The method according to claim 3 , wherein a decrease in the lowermost one of the measured annular interval static densities indicates a decrease in the density of the formation cuttings and an increase in the lowermost one of the measured annular interval static densities indicates an increase in the density of the formation cuttings.

5. The method according to claim 2 , wherein:
(e) further comprises comparing the measured annular interval static densities with modeled static densities; and
(f) further comprises evaluating a difference in at least one of the measured annular interval static densities and a corresponding one of the modeled static densities as an indicator of a change in the density of the formation cuttings.

6. The method according to claim 2 , wherein:
(d) further comprises processing the annular pressure measurements to compute a plurality of equivalent top of fluid levels while drilling in (a);
(e) further comprises monitoring the equivalent top of fluid levels with time while drilling in (a); and
(f) further comprises evaluating a change in at least one of the equivalent top of fluid levels as an indicator of a change in the density of the formation cuttings.

7. The method according to claim 2 , wherein:
(d) further comprises processing the annular pressure measurements to compute a plurality of annular surface back pressures while drilling in (a);
(e) further comprises monitoring the annular surface back pressures with time while drilling in (a); and
(f) further comprises evaluating a change in at least one of the annular surface back pressures as an indicator of a change in the density of the formation cuttings.

8. The method according to claim 2 , wherein (b) further comprises processing the plurality of measured annular interval static densities to compute at least one interval density of the formation cuttings.

9. The method according to claim 1 , wherein (f) further comprises evaluating a change in a lowermost one of the computed annular interval densities as an indicator of a change in the cuttings density.

10. The method according to claim 9 , wherein a decrease in the lowermost one of the computed annular interval densities indicates a decrease in the density of the formation cuttings and an increase in the lowermost one of the computed annular interval densities indicates an increase in the density of the formation cuttings.

11. The method according to claim 9 , wherein (f) further comprises evaluating a change in the lowermost one of the computed annular interval densities at a first time and a change in another of the computed annular interval densities at a second later time as an indicator of a change in the density of the formation cuttings.

12. The method according to claim 1 , wherein:
(e) further comprises comparing the computed annular interval densities with modeled circulating densities; and
(f) further comprises evaluating a difference in at least one of the computed annular interval densities and a corresponding one of the modeled circulating densities as an indicator of a change in the density of the formation cuttings.

13. A method for computing an interval cuttings density during a downhole drilling operation, the method comprising:
(a) rotating a drill bit in a subterranean wellbore, the drill bit being deployed in a drill string including first and second axially spaced along string pressure sensors, said rotating operative to drill the wellbore and produce formation cuttings which are transported to a surface location via drilling fluid in a wellbore annulus;
(b) using the first and second along string pressure sensors to make first and second subsurface annular pressure measurements at corresponding first and second measured depths in the wellbore;
(c) transmitting the first and second pressure measurements to a processor;
(d) causing the processor to process the first and second annular pressure measurements to compute an annular interval density of the drilling fluid between the first and second measured depths in the wellbore; and
(e) causing the processor to process the annular interval density computed in (d) to compute a density of the formation cuttings produced in (a) and located between the first and second measured depths in the wellbore.

14. The method according to claim 13 , wherein (e) further comprises:
(i) computing a static annular interval density via subtracting a modeled annular friction component from the annular interval density computed in (d); and
(ii) processing the static annular interval density computed in (i) to further compute the density of the formation cuttings.

15. The method according to claim 14 , wherein (ii) further comprises processing the static annular interval density computed in (i), a volume fraction of drilling fluid in the wellbore annulus, a density of the drilling fluid in the wellbore annulus, and a volume fraction of cuttings in the wellbore annulus to compute the density of the formation cuttings.

16. The method according to claim 15 , wherein the density of the formation cuttings is computed according to the following mathematical equation:

SG
cuttings

=

MA_ISD
-

f
mud

·

SG
mud

f
cuttings

Assignees

• Rasmus John
• Lesso William
• James John
• Tollefsen Edward M
• Scott Paul
• Weber Amanda L
• Turner Marcus
• Schlumberger Technology Corp

Inventors

• Rasmus John
• Lesso William
• James John
• Tollefsen Edward M
• Paul Scott
• Weber Amanda L
• Turner Marcus

Classifications

• E21B47/06

  Measuring temperature or pressure · CPC title

• E21B49/005 Primary

  Testing the nature of borehole walls or the formation by using drilling mud or cutting data · CPC title

• E21B47/10 Primary

  Locating fluid leaks, intrusions or movements · CPC title

• E21B49/003

  by analysing drilling variables or conditions (E21B49/005 takes precedence; systems specially adapted for monitoring a plurality of drilling variables or conditions E21B44/00) · CPC title

• E21B47/003

  Determining well or borehole volumes · CPC title