Engineering methodology to treat severe loss zones with thixotropic cement system

Patent metadata

Field	Value
Publication number	US-10344544-B2
Application number	US-201515556601-A
Country	US
Kind code	B2
Filing date	Apr 7, 2015
Priority date	Apr 7, 2015
Publication date	Jul 9, 2019
Grant date	Jul 9, 2019

Abstract

A method of treating lost circulation issues stemming from loss zones during the drilling and cementing process through the utilization of a thixotropic cement. The method comprises the steps of encountering a loss zone in a bore hole during drilling or running casing and pumping a treatment fluid into the loss zone, wherein the treatment fluid is a gel capable of gelling, breaking when sheared, and building back shear strength after shearing is removed.

First claim

What is claimed is:

1. A method of treating a loss zone during drilling or running casing, the method comprising the steps of:
(1) encountering the loss zone in a bore hole during the drilling or running casing;
(2) determining a rheology model of a thixotropic cement system, wherein the rheology model comprises a relationship between shear rate and viscosity during a flow regime of the thixotropic cement system and a relationship between gel strength and time during a quasi-static or no-flow regime of the thixotropic cement system, wherein the step of determining the rheology model of the thixotropic cement system comprises the steps of:
(a) determining a required minimum gel strength of the thixotropic cement system;
(b) determining an amount of time needed to reach the required minimum gel strength;
(c) determining a maximum gel strength of the thixotropic cement system;
(d) determining an amount of time needed to reach the maximum gel strength of the thixotropic cement system;
(e) determining a maximum pressure output of a pump;
(f) determining a required pressure level needed to circulate the thixotropic cement system;
(g) confirming that the thixotropic cement system can be recirculated before the maximum gel strength is reached; and
(h) determining a volume of the thixotropic cement system required to fill the loss zone;

(3) designing and testing the thixotropic cement system to confirm adherence to the determined rheology model;
(4) pumping the designed and tested thixotropic cement system into the loss zone, wherein the thixotropic cement system is a gel and (i) gels (ii) breaks when sheared and (iii) builds back shear strength after shearing is removed.

2. The method of claim 1 , wherein the thixotropic cement system repeatedly (i) gels (ii) breaks when sheared and (iii) builds back shear strength after shearing is removed.

3. The method of claim 1 , wherein the minimum gel strength is a point at which the thixotropic cement system in the bore hole does not experience flow due to hydrostatic column pressure above the loss zone.

4. The method of claim 1 , wherein the maximum gel strength is a point at which the thixotropic cement system cannot be recirculated in a drill string or in the bore hole.

5. The method of claim 1 , wherein the step of determining the volume of the thixotropic cement system required to fill the loss zone comprises the steps of: measuring a volumetric loss rate of drilling fluid in the bore hole; and estimating a fracture geometry and dimensions of the loss zone.

6. The method of claim 1 , further comprising the step of confirming that the thixotropic cement system can be pumped through a bottom hole assembly of a drilling rig before the step (4) of pumping the thixotropic cement system into the loss zone.

7. The method of claim 6 , further comprising the step of confirming that tripping is possible before the step (4) of pumping the thixotropic cement system into the loss zone.

8. The method of claim 7 , further comprising the steps of: estimating a tripping time before the step (4) of pumping the thixotropic cement system into the loss zone; and estimating an amount of time necessary to swap out a cement pump for a rig pump before the step (4) of pumping the thixotropic cement system into the loss zone.

9. The method of claim 8 , further comprising: before the step (4) of pumping the thixotropic cement system into the loss zone, estimating a maximum down time allowable before the thixotropic cement system reaches the maximum gel strength.

10. The method of claim 9 , further comprising: incorporating the maximum down time allowable into the rheology model.

11. The method of claim 1 , further comprising: determining acid solubility of the thixotropic cement system; stopping flow of the thixotropic cement system once it has filled the loss zone; and determining whether a plug formed by the thixotropic cement system is permanent.

12. A method of treating a loss zone in a bore hole during drilling with a thixotropic cement system, the method comprising the steps of:
(1) drilling with a drilling fluid until encountering the loss zone;
(2) determining a rheology model of the thixotropic cement system, wherein the rheology model comprises a relationship between shear rate and viscosity during a flow regime of the thixotropic cement system and a relationship between gel strength and time during a quasi-static or no-flow regime of the thixotropic cement system, wherein the step of determining the rheology model of the thixotropic cement system comprises the steps of:
(a) measuring a volumetric loss rate of the drilling fluid in the bore hole;
(b) estimating a fracture geometry and dimensions of the loss zone;
(c) measuring a depth of the loss zone;
(d) measuring an annular fluid density;
(e) estimating an annular hydrostatic pressure above the loss zone;
(f) estimating a minimum gel strength of the thixotropic cement system, wherein the minimum gel strength is a point at which the thixotropic cement system in the bore hole does not experience flow due to hydrostatic column pressure above the loss zone;
(g) estimating a column length of the thixotropic cement system in the loss zone;
(h) estimating a maximum pump pressure;
(i) estimating a maximum allowed pressure for recirculation per unit length of the thixotropic cement system column;
(j) estimating a maximum allowed gel strength; and
(k) estimating a time to reach the maximum allowed gel strength;

(3) designing and testing the thixotropic cement system to confirm adherence to the determined rheology model;
(4) pumping the designed and tested thixotropic cement system to the loss zone.

13. The method of claim 12 , further comprising the step of confirming that the thixotropic cement system can be pumped directly through a bottom hole assembly or that tripping is required.

14. The method of claim 13 further comprising the step of estimating the pressure for recirculation per unit length of the thixotropic cement system.

15. The method of claim 14 , further comprising the step of confirming that residual thixotropic cement system, after a maximum allowable down time with attained gel strength, can be circulated back out of the bore hole after treating the loss zone.

16. The method of claim 15 , wherein the step of determining whether the residual thixotropic cement system with attained gel strength can be circulated back out of the bore hole after treating the loss zone comprises the steps of:
designing the thixotropic cement system with desired rheological behavior;
confirming rheology readings;
performing an on-off test of the thixotropic cement system to confirm that the thixotropic cement system will regain pumpable viscosity after circulation is stopped; and
performing acid solubility tests on the thixotropic cement system.

17. The method of claim 15 , further comprising the steps of:
confirming that the thixotropic cement system can be pumped using a rig pump;
determining a time needed to swap the rig pump and a cement pump;
estimating a tripping time;
pumping the thixotropic cement system into the loss zone; and
allowing the thixotropic cement system to enter a quasi-static or no flow period.

Assignees

• Halliburton Energy Services Inc

Inventors

• Ravi Krishna M
• Patil Rahul Chandrakant
• Patil Sandip Prabhakar
• Jandhyala Siva Rama Krishna
• Gahlawat Ravinder

Classifications

• E21B21/003 Primary

  Means for stopping loss of drilling fluid (plastering the borehole wall E21B33/138) · CPC title

• C09K8/487

  Fluid loss control additives; Additives for reducing or preventing circulation loss · CPC title

• C09K8/42

  Compositions for cementing, e.g. for cementing casings into boreholes; Compositions for plugging, e.g. for killing wells (compositions for plastering C09K8/50) · CPC title

• C09K8/428

  for squeeze cementing, e.g. for repairing · CPC title

• C09K8/50 Primary

  Compositions for plastering borehole walls, i.e. compositions for temporary consolidation of borehole walls (compositions for consolidating loose sand or the like around wells C09K8/56) · CPC title