Method of Treating a Subterranean Formation using a Rheology Model for Fluid Optimization

Abstract

Subterranean formation treatment methods incorporating a rheology model which enables prediction of fluid rheology properties during a treatment operation, where the foundation of the model is a description of the reaction chemistry which describes how the number of crosslinks and broken polymer linkages develops in time under the influence of crosslinkers, breakers, and/or thermally induced effects and pressure effects. In one aspect, when used as a tool for simulating the fluid viscosity, the model can help optimizing the fluid design and optional breaker schedule for a hydraulic fracturing treatment.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings: FIG. 1 show the viscosity reduced by the viscosity at complete crosslink as a function of the crosslink concentration.

FIG. 1 illustrates the ratio of partially crosslinked fluid viscosity to fully crosslinked fluid viscosity as a function of the crosslink concentration.

FIG. 2 illustrates dimensionless crosslinking viscosity increment as a function of the generalized shear rate where the transition between Newtonian and power law behavior occurs at a generalized shear rate of 1.

FIG. 3 shows experimental and simulated rheology for a fluid containing 20 ppt guar polymer and 3.1 gpt borate crosslinker solution, without breaker.

FIG. 4 illustrates experimental and simulated rheology for a fluid containing 30 ppt guar polymer, 4.4 gpt borate crosslinker solution and 2.2 ppt ammonium persulfate

FIG. 5 is a plot of experimental and simulated rheology for a fluid containing 24.9 ppt guar polymer, 2.2 gpt borate crosslinker solution, 1.1 ppt ammonium persulfate and 0.5 gpt triethanolamine solution

FIG. 6 shows calculated versus experimental viscosities during a Fann 50 experiment where the spikes correspond to the shear ramps, where the shear rate is ramped down from 100 s⁻¹ (base) to 25 s⁻¹ and back up to the base shear rate.

FIG. 7 illustrates experimental and calculated viscosity profiles for the Fann 50 experiment shown in FIG. 6.

FIG. 8 is a plot of calculated vs. experimental viscosities during a low-shear rheology experiment for a gel containing 30 ppt guar polymer and 3.6 gpt borate crosslinker solution at 125° F.

FIG. 9 is a plot of calculated vs. experimental viscosities profiles for a gel containing 30 ppt guar polymer, 3.6 gpt borate crosslinker solution at 125° F.

Claims

1. A method for treating a subterranean formation penetrated by a wellbore, the method comprising: a. predicting a plurality of formation treatment scenarios for a treatment fluid comprising a polymer and a crosslinker using a fluid rheology model comprising: i. inputting a concentration of polymer and a concentration of crosslinker,ii. inputting temperature and pressure and shear rate profiles over the course of the treatment,iii. determining the concentration of crosslinks over the course of the treatment based upon the input values from i. and ii,iv. determining the fluid rheology over the course of the treatment based on the concentration of crosslinks over the course of the treatment;b. selecting a treatment scenario which provides optimal fluid rheology properties during the course of treatment;c. preparing and injecting the treatment fluid into the wellbore; andd. treating the subterranean formation.

2. The method of claim 1 further comprising inputting a concentration of breaker.

3. The method of claim 1 further comprising inputting the concentration of one or more pH modifiers over the course of the treatment.

4. The method of claim 1 wherein in the selection of a treatment scenario is based upon incorporating a minimum amount of polymer.

5. The method of claim 4 wherein in the selection of a treatment scenario is based upon incorporating a minimum amount of polymer and optimal clean-up after treatment.

6. The method of claim 1 further comprising inputting the concentration of a crosslinking delay agent over the course of the treatment.

7. The method of claim 1 further comprising monitoring the stimulation treatment and evaluating the fluid performance downhole based upon real-time monitoring the fluid composition at the surface.

8. The method of claim 1 further comprising inputting fluid pumping rate, wellbore configuration, and fluid travel time to a treatment zone.

9. The method of claim 1 as used in a hydraulic fracturing simulator whereby fluid rheology is calculated to simulate the fracture placement and an optimal pumping sequence is determined.

10. The method of claim 1 wherein the fluid rheology is determined by coupling irreversible reactions that the polymer undergoes caused thermal effects or by oxidizing or enzyme agent, with equilibrium reactions of the crosslinker and polymer as a function of time, temperature, pressure, polymer concentration, and crosslinker concentration.

11. The method of claim 1 as used for fracturing a subterranean formation.

12. The method of claim 1 as used for monitoring fluid placement during fracturing treatments, acidizing treatments, wellbore cleanout operations, gravel packing operations, acid diversion treatments, and fluid loss control operations.

13. The method of claim 1 wherein the polymer is selected from the group consisting of guar, hydropropyl guar (HPG), carboxymethyl guar (CMG), carboxymethylhydroxypropyl guar, cellulose, hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), carboxymethylhydroxyethylcellulose (CMHEC), xanthan, diutan, whelan gum, polyacrylamide, polyacrylate polymers, and wherein the crosslinker is a zirconium, titanium or borate based crosslinker.

14. The method of claim 1 wherein the polymer is guar and the crosslinker is a borate based crosslinker.

15. The method of claim 1 further comprising considering pressure effects on the effectiveness of a borate based crosslinker in determining the fluid rheology over the course of the treatment.

16. The method of claim 1 wherein the concentration of crosslinks is about 5×10−8 mole/L or greater.

17. The method of claim 1 wherein the fluid further comprises a proppant, and concentration of the proppant is inputted into the model.

18. The method of claim 1 wherein the concentration of polymer ranges from about 15 to about 40 pounds per thousand gallons, preferably from about 15 to about 35 pounds per thousand gallons, more preferably from about 20 to about 30 pounds per thousand gallons.

19. The method of claim 1 wherein the concentration of polymer is about 15 pounds per thousand gallons or less, preferably from about 1 to about 10 pounds per thousand gallons.

20. A method for treating a subterranean formation penetrated by a wellbore, the method comprising: a. predicting a plurality of formation treatment scenarios (fluid formulation and treatment schedule) for a fluid comprising a polymer and a crosslinker, using a fluid rheology model comprising: i. inputting a concentration of polymer and a concentration of crosslinker,ii. inputting temperature, pressure and shear rate profiles over the course of the treatment,iii. determining the concentration of crosslinks over the course of the treatment based upon the input values from i. and ii,iv. determining the fluid rheology over the course of the treatment based on the concentration of crosslinks over the course of the treatment;b. selecting a treatment scenario which provides optimal fluid rheology properties after completion of the treatment;c. preparing and injecting the treatment fluid into the wellbore; andd. treating the formation.

21. A method for treating a subterranean formation penetrated by a wellbore, the method comprising: a. predicting a plurality of formation treatment scenarios (fluid formulation and treatment schedule) for a fluid comprising a polymer, using a fluid rheology model comprising: i. inputting a concentration of polymer,ii. inputting temperature, pressure and shear rate profiles over the course of the treatment,iii. determining the fluid rheology over the course of the treatment by considering concentration of polymer, and temperature, pressure and shear rate profiles over the course of the treatment;b. selecting a treatment scenario which provides optimal fluid rheology properties during the course of treatment;c. preparing and injecting the treatment fluid into the wellbore; andd. treating the formation.