SPE 95287

Measurement of Proppant Transport of Frac Fluids

Phillip C. Harris, Ronnie G. Morgan, Stanley J. Heath, Halliburton

Copyright 2005, Society of Petroleum Engineers

This paper was prepared for presentation at the 2005 SPE Annual Technical Conference and

Exhibition held in Dallas, Texas, U.S.A., 9 - 12 October 2005.

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Abstract

The object of hydraulic fracturing is to produce a propped

fracture extending from the wellbore. Extensive time and

effort are expended in measuring theological properties of

crosslinked fluids (without proppant) under simulated

downhole temperature and shear-history conditions.

Normally, it is assumed that if a fluid meets certain minimum

viscosity conditions, it will transport proppant successfully.

Measurements of actual proppant transport under dynamic

simulated downhole conditions have been attempted and

described, but such measurements have been very

cumbersome and require significant equipment and expense to

execute. Such measurements are well beyond the scope of

routine QA/QC analyses.

A proppant viscometer recently constructed can measure

fracturing fluids containing propping agents across a wide

range of concentrations. The device was designed to work as a

conventional Farm Model 50-type viscometer. This unique

viscometer has been used to measure typical fracturing fluids

containing realistic concentrations of proppants, at

temperatures and times up to several hours, representative of

actual fracturing treatments. The measurements show regions

of elastic transport typical of viscoelastic fracturing fluids

where proppant is transported efficiently, usually followed by

regions of purely viscous transport where proppant slowly

settles.

The advantage of the new proppant viscometer is that all

components of a fracturing fluid, including proppant, can be

tested. Shear-history effects of proppants on frac fluids are

usually unknown or ignored, but such effects were observed in

this work. Breakers were usually added to the fluids, showing

reasonable times when the crosslinked fluid no longer

transported proppant efficiently and proppant began to settle.

This paper shows how different types of fracturing fluids

can support proppant based on their chemical type, i.e. metal

and borate crosslinked fluids, linear gel fluids, and surfactant

gel fluids. Proppant concentrations are also considered. The

physical characteristics of the proppant viscometer are also

addressed.

Introduction

Most hydraulic-fracturing treatments use a gelled fluid to

create a subterranean fracture and partially fill the fracture

with propping agents. When the fracture closes and the fluid is

recovered, a conductive channel into the reservoir remains.

Proppant transport is a function of (1) wellbore and fracture

geometry; (2) volumetric rate; (3) proppant size, concentration

and specific density; and (4) cartier-fluid rheology.

Instruments such as Farm Model 50 viscometers are available

for measuring viscosity at high temperatures and pressures,

but elasticity is much more elusive to measure. Additionally,

most viscometers, such as the Model 50, are designed only to

handle the "clean fluid systems," e.g. without proppant. By

default, we generally assume that higher viscosities will do a

better job of transporting proppant, as well as generating the

desired fracture geometry. There have been several attempts1-9

to characterize transport properties of fluids using modified

bench-scale viscometers or through large slot or pipeline

apparatus, but those efforts are very expensive and are not

performed using routine quality-assurance measures.

Several rheological properties directly impact a frac fluid’s

performance: (1) apparent viscosity, (2) yield stress, (3)

dynamic viscosity, (4) rheomalaxis (irreversible thixotropy),

(5) viscoelasticity (for example G’, G"), and (6) the related

issue of turbulent-drag reduction. In laboratory research,

sample volume is often very limited, thus necessitating

rheological testing and evaluation of small quantities. Also,

most bench-top rheometers use batch mode, that is, small

samples are placed in a testing chamber as opposed to flowthrough testing, as is the case for pipe viscometers. This

presents the challenge of simultaneously:

1. Imparting viscometric shear history that simulates the

wellbore travel path.

2. Not exceeding the proper mechanical energy input;

the bench-top batch process should impart about the

same amount of integrated work as the wellbore path.

3. Maintaining satisfactory thermal balance, e.g. being

sure not to create localized "hot spots" in the benchtop process because of its batch mode of operation.

In the case of most polymer-based fracturing fluids, the

capability to transport proppant is directly related to their

"rheological equations of state (RES)." Extent of crosslinking,

breaking, shear history, and volume-average shear rate are

HESI300394
2 SPE 95287

major factors affecting a fluid’s RgS.10-11 As an illustration,

Table 1 is a summary showing how fracture height and width

affect volume-average shear rates for a Newtonian fluid.

Where viscous drag dominates, as in the classical case of a

two-winged vertical fracture with parallel-plate geometry, the

challenge in proppant transport is to ensure that vertical

settling time is much greater than horizontal travel time.

Sufficient vertical settling time allows the particle to reach a

maximum horizontal distance, thus avoiding a duning effect.

Table 2 is a simple illustration of the ratio of horizontal

velocity to vertical settling velocity of 20/40 sand being

carried by a 500 cp Newtonian fluid. Table 2 illustrates the

sensitivity of proppant transport to fracture geometry. The

shaded areas were selected as examples in which the

horizontal transport time was at least 50 times greater than the

vertical settling times.

In the case of crosslinked gels, the elastic forces are

designed to dominate, preventing any substantial viscous

settling during the fracturing and placement of proppant.

Morris12 presents the case that a minimum value of G’

(oscillatory elastic modulus) of 10 to 12 Pa’s is sufficient for

most 20/40 frac sands. The complex viscoelastic nature of

crosslink fracturing fluids presents a dilemma for the

fracturing rheologist. Conventional rheometers are designed

for measuring viscoelastic properties through well-controlled

oscillatory deformations that are small, non-destructive, and

within the linear elastic range. However, the actual fracturing

process involves large amounts of shear strain of multiple

orders of magnitude, well beyond the linear elastic range. As

the breaker reaction begins to dominate, the transport

mechanism shifts from elastic to viscous, leading to settling

caused by the low viscosity of the broken fluid system.

The Fann Model 50 viscometer was designed for

characterizing fracturing gels under simulated downhole

temperature-time conditions. However, the Model 50 and most

other bench-top viscometers/rheometers are not adequately

equipped to handle proppant-laden fluids. In the case of

concentric cylinders, the centrifugal forces tend to stxatify the

particles, thus resulting in nonrelevant data. In cone-plate and

plate-plate viscometers, the small gaps necessary to provide

torque sensitivities result in "particle jamming." Additionally,

the large density differences between most proppants and

conventional fracturing fluids result in settling during testing,

thus producing unreliable results.

Many researchers have modeled and/or measured the

effects of fluid rheology and particle size, shape, and density

on suspension at_tributes in either single-particle systems or at

dilute concentrations, in which particle-to-particle interactions

are neglected. Others have attempted to include the impact of

particle-to-particle collisions.13-15

Morgan et al.16 presented a bench-top device and model for

predicting the apparent viscosity of proppant-laden fluids for

Newtonian and Power-law fluids with a wide range of particle

sizes and concentrations. Their work was based on a

viscometer uniquely designed to keep highly concentrated

dense particles suspended in fluids while measuring "volumeaveraged shear stresses and shear rates." The work was

limited to atmospheric temperature and pressure and did not

include crosslinked gels. Table 3 summarizes the experimental

limits of the work. The impact of particle concentration

followed Huggins theory, that is, that apparent viscosity of the

bulk slurry was a function of particle concentration, as shown

in Fig. 1.

The proppant viscometer described here measures in the

highly concentrated range with 7.5 power, according to Fig. 1.

We have designed and tested an apparatus capable of routine

measurement of gelled fracturing fluids containing wide range

of proppant particles under downhole temperatures, ranging

from linear to fully crosslinked, to broken gels. By measuring

various types of fracturing fluids, it is possible to classify the

transport properties of each fluid type. By adding breaker

chemicals to fluid, it is possible to determine the length of

time a fluid maintains its transport capability, or whether the

proppant will settle quickly.

Experimental

Base gel fluid was mixed in a blender with polymer, buffers,

surfactant, and clay control in tap water. A 500-mL sample of

base gel fluid and 725 g of 20/40 mesh proppant (145 g/100

mL) were stirred at moderately high speed with an overhead

stirrer. Reactive additives, i.e., crosslinker and breaker, were

added while stirring. The slurry was quickly transferred to the

cup and placed on the proppant viscometer. The transferring

operation required about 1 minute. The cup was rotated at 25

RPM, with an estimated volume-average shear rate of 6 sec-1.

Torque was monitored while the sample was heated at

5°F/min. Volume-average viscosity (VAV) and temperature

data were plotted vs. time.

Description of Proppant Viscometer

The proppant viscometer17 is based on a Fann Model 50-type

viscometer with modified bob and cup. The proppant

viscometer has an inner sensing surface composed of flags, in

place of the concentric cylinder design of the Model 50

viscometer (see Fig. 2). To aid mixing within the cup,

protrusions were welded to the inner walls of the cup. Proper

clearances were provided between the flags and the wall

extensions to help prevent proppant from sticking between the

surfaces. As the flags on the moving cup sweep by the static

flags on the central sensing shaft, a cyclic torque is measured.

The oscillating force contains both viscous and elastic

components.

The proppant viscometer has complicated geometric

surfaces, making calculation of shear rate difficult. However,

laboratory personnel approximated volume-average shear rate

by studying known fluids. The resistance to movement of a

slurry increases as proppant concentration increases.

Placement of the mixing and sensing surfaces toward the

bottom of the cup allows greater sensitivity to concentrating of

proppant as it settles. An increase in torque indicates that

proppant is settling.

Theory

Viscometry studies by Steffe and Morganis-2° were used to

develop the following equations for estimating volumeaverage shear rates, shear stresses, and viscosities for the

device described in Fig. 2.

 vol = kl (RPM) ................................... (1)

HESI300395
SPE 95287 3

fro1 = k2 (Torque) ............................... (2)

where: 7~o1 is the volume-average shear rate within the novel

viscometer;’ ~o1 is the volume-average shear stress; and ~-~o1

is the volume-average viscosity (VAV) within the modified

Model 50 viscometer. The value of k1 is unique to the

geometry of the device and slightly related to the sample

volume, while the value of k2 is unique to the torquemeasuring device. Newtonian viscosity standards and Powerlaw fluids were used to quantify the values of kl and k2 for

the fracturing fluid/proppant systems used in this study.

Proppant Viscometer Response for Linear Gel Fluids

The volume-average viscosity (VAV) is a product of fluid

viscosity, particle concentration and cup RPM. When the sand

concentration was held constant at 12 lb/gal and noncrosslinked polymer concentration varied, two separate effects

were observed in the curves, as shown in Fig. 3a. The most

noticeable effect is that the slope of the curve decreased as

polymer concentration increased. Once the elastic transport

forces no longer dominate, the particles begin to settle at a rate

dependent upon their size, density, concentration, and the

viscosity of the fluid medium. The slope of the VAV vs. time

curves are defined as rate of viscous settling (RVS) values,

which are plotted in Fig. 3b. Proppant settled very rapidly for

the 40-1b/Mgal base-gel fluid at 75°F and 6 see-l; whereas

settling may not have been complete in the 100-1b/Mgal fluid

until about 4 hours. The slope of these lines is useful to

describe purely viscous settling behavior in more complex

fluid systems, such as those with crosslinker and breakers.

The second effect is that higher polymer concentrations

have a higher torque at zero time, where all the proppant is

evenly distributed throughout the fluid. This zero-time

intercept value is a function of base-gel viscosity and particle

concentration. Surfactant gel fluids behaved similarly to noncrosslinked polymer fluids. Micelles and vesicles that

comprise surfactant gels are analogous to polymer gels of high

molecular weight, whose viscous behavior depends solely on

hydrodynamic volume interference and limited entanglement,

rather than upon crosslinking.

Proppant Viscometer Response for Crosslinked Gels

Crosslinked gels respond very differently from linear-base

gels. Their lower RVS slope indicates that even low polymer

concentrations of crosslinked fluid may transport better than

high polymer concentrations of noncrosslinked fluids. This

fact indicates a fundamental difference between the fluids.

Noncrosslinked fluids support particles on the basis of viscous

forces; whereas crosslinked fluids are tied together in a

network structure. The network provides elasticity to the fluid

structure.

The initial decline in the proppant viscometer response for

crosslinked slurry (lowest curve of Fig. 4) is caused by

temperature thinning of the supporting fluid. Once

temperature is reached (upper curve), the VAV maintains a

stable reading, decreasing only slightly as the breaker works to

reduce the polymer network. This stable, low-VAV response

is the "elastic transport region," where virtually perfect

proppant transport occurs. Eventually, the breaker acts to

sever sufficient network connections and allows particles to

fall, resulting in the "onset of sand settling." Settling usually

begins at a low rate, which may increase as the breaker

continues to decrease the degree of networking in the polymer

fluid. This response is the "viscous settling region," where

settling approximates that of a non-crosslinked polymer

solution. The slope in this region may be compared to RVS

slopes of Fig. 3 as an indicator of the viscous state of the fluid.

Another curve may be superimposed on the VAV curve of

Fig. 4. The dashed line (middle curve) represents a typical

Fann Model 50 viscometer response of the same sample

without sand. This curve shows a decline in viscosity because

of the effects of chemically breaking the polymer. By itself,

this curve shows no indication of whether the fluid will

transport sand. By coupling the Model 50 curve with the sandtransport curve, it is possible to correlate viscosity with the

time the onset of sand settling occurs. Fluids may then be

compared to determine the minimum viscosity at which they

will give proppant transport. However, both fluids must have

similar shear histories during the crosslinking reaction for this

procedure to be valid.

A clear plastic cup was constructed for the proppant

viscometer to allow visualization of proppant settlement to

coincide with torque measurements. The clear cup reinforced

the VAV measurements to give greater confidence in the

technique. Fig. 5 shows a low-temperature, metal-crosslinked

fluid with an enzyme breaker. Photographs of the clear cup

containing the slurry are superimposed on the plot of VAV at

corresponding times. The arrows point to the top of the

proppant bed. As the proppant settled from breaker activity

over time, the VAV value increased, thus validating similar

measurements at higher pressure and temperature in the

stainless steel cup.

Fig. 6a shows a concentration series of low-polymer

metal- crosslinked fluids containing oxidizer breaker at 250°F.

The initial low-viscosity region parallel to the time axis is the

elastic transport region, where virtually no settling occurs.

Proppant is supported by a network structure having crosslink

bonds between polymer strands. As the viscometer cup rotates

at 25 RPM, the network stretches for about 1A sec and relaxes

for 1A sec alternately, producing torque oscillations. For the

metal-crosslinked elastic fluid, the oscillations have small

amplitude. Breaker actively reduces the network structure

within the elastic region until proppant is no longer supported

perfectly and the onset of sand settling is reached. Following

that point, we encounter viscous settling, where the increasing

slope indicates that proppant concentration is increasing at the

bottom of the cup. The slopes of the VAV vs. time curves in

Fig. 6a were computed and are plotted in Fig. 6b to illustrate

the sensitivity of this novel proppant viscometer to

characterize both the elastic proppant transport regime and

also the rate at which proppant settles during breaking. For the

viscous settling region, the amplitude of the torque oscillations

is greater and increases as proppant settles out. Oxidizer

HESI300396
4 SPE 95287

breaker was a practical addition to these tests, because without

breaker, the onset of sand settling would be much longer.

The capability of the metal-crosslinked fluid to transport

proppant elastically (judged by constant VAV value) was not

improved by higher polymer concentration up to the onset of

sand settling. The higher polymer concentration did increase

the time to arrive at the onset of sand settling. Undoubtedly

the fluids with higher polymer concentration had more

molecular interaction or entanglement, and longer time was

required for the breaker to reduce those network interactions

to the point of releasing sand for settlement.

Fig. 7a shows the effect of breaker concentration on a

metal-crosslinked fluid at 250°F. With no oxidizing breaker

present, the fluid continues to support proppant elastically for

an extended period. When breaker is added, transport

capability is relatively sensitive to breaker concentration,

indicating that accuracy of metering the breaker is important

to good proppant placement. Once again, the RVS were

computed and are shown in Fig. 7b. Note the sensitivity of

the proppant viscometer to detect changes in dynamic settling

of the proppant.

Another breaking mechanism for metal-crosslinked fluids

is acid hydrolysis. Fig. 8 shows a fluid that can be crosslinked

from pH 5 to 10. The fluid can be readily stabilized at neutral

and alkaline pH values, but acid hydrolysis will eventually

break down the polymer network. The fluid character changes

from elastic to viscous transport, allowing proppant to settle.

The appearance of proppant transport plots for boratecrosslinked fluids differed significantly from plots for metalcrosslinked fluids (Fig. 9). Short-term oscillations for these

fluids at 100°F were more intense than for metal-crosslinked

fluids, indicating greater elasticity. The intensity of the

oscillations makes the curves more difficult to interpret.

Approximate VAV values for proppant transport (22,500 cP)

and proppant settling (37,500 cP) are indicated by dashed

lines. Below the lower line, proppant is transported elastically.

Above the upper line, proppant is being deposited. Between

the two lines, proppant settles in a viscous mode. Very low

polymer concentrations, i.e. 15 lb/Mgal, showed elastic

transport for a very short period of time, then the proppant

settled very quickly. At 20 lb/Mgal, the fluid maintained

elastic transport for about 2 hours before rapid settling

occurred. The 25-1b/Mgal fluid without breaker transported

proppant for almost 3 hours before a rapid increase could be

detected; the transition from elastic to viscous transport is not

very obvious.

Discussion

Data for fracturing fluids in the proppant viscometer illustrate

three major fluid classes having differences in capability to

transport proppant. The first class of fluids does not have a

network structure and does not transport proppant perfectly.

These fluids include Newtonian fluids (oil and water), and

non-Newtonian, non-crosslinked polymer fluids, oil gels, and

surfactant gels. This first class transports by viscosity alone

and settling occurs during transport, depending upon flow rate

and viscosity. It may be possible to transport proppant

efficiently with combined rate and viscosity if the settling time

is not too long, but such a combination would likely result in

very high pumping pressures.

A second class of fluids is the metal-crosslinked group.

These fluids exhibit viscoelasticity. When polymer

concentration and crosslink density are high enough, proppant

is transported perfectly, without settling, usually at a low

pumping pressure. Once the perfect transport threshold is

achieved, adding more polymer or crosslinker to increase

viscosity does not improve transport, but may increase

pumping pressure. Some breaker mechanism is required to

initiate disruption of the network structure and allow settling

to begin.

A third class of fluids is the borate-crosslinked group.

Borate fluids have a transient network structure. The state of

the crosslink network is dependent upon shear rate as well as

fluid composition. When borate fluids are static long enough

to become relaxed, settling of proppant may occur in the

viscous settling mode. However, when some small shear rate

is imposed on the fluid, elasticity increases and the fluid acts

to transport perfectly. Some minimum degree of shear must be

maintained on borate fluids to maintain the elastic network

condition.

Foamed fluids were also measured on the proppant

viscometer. Foams made with noncrosslinked polymers

exhibited viscous settling, but at a slower rate than the neat

liquid phase alone. The retarded settling of 70% quality foams

indicates the presence of some fluid structure, although not

necessarily the same as a crosslinked polymer network. It may

be that the retardation is an indication of a yield point in the

foam. One would expect that crosslinked foams would

transport at least as well as the external liquid-phase gel.

The proppant viscometer shows that borate-crosslinked

and metal-crosslinked fluids are very different in structure and

in capability to transport proppant. It also indicates that

measurements of viscosity, such as in a couette viscometer, do

not forecast the capability of a fluid to transport proppant. We

found that low-polymer metal crosslinked fluids can transport

proppant perfectly for long periods of time, even though their

couette viscosity readings are not very high. On the other

hand, low-polymer borate fluids produce very impressive

couette viscosity values, often 10 times as high as the metalcrosslinked fluids, but their proppant transport may not be as

good.

Conclusions

A modified Farm Model 50-type viscometer has produced

measurements indicating the capability of a fracturing fluid to

transport proppants. The proppant viscometer can further

distinguish between fluid types having either viscous or elastic

components. Proppant is included as a component of the fluid,

so chemical effects from the presence of proppant material can

be observed.

Three main classes of fracturing fluids were described

according to transport capability:

 ̄ Purely viscous fluids. These fluids include

Newtonian fluids (oil and water), non-Newtonian

non-crosslinked polymer fluids, oil gels, and

surfactant gels. This class transports by viscosity

alone and settling occurs during transport according

to flow rate and viscosity. In these cases, it is

important to ensure that the ratio of the fractureHESI300397
SPE 95287 5

transport velocity is much greater than the verticalsettling velocity.

Metal-crosslinked viscoelastic fluids. Metalcrosslinked fluids have a permanent network

structure. When polymer concentration and crosslink

density are high enough, proppant is transported

efficiently, without settling,

Borate-crosslinked viscoelastic fluids. Boratecrosslinked fluids have a transient network structure.

The state of the crosslink network is dependent upon

shear rate as well as fluid composition. Some

minimum degree of shear must be maintained on

borate fluids to maintain the elastic network

condition.

Acknowledgements

The authors would like to acknowledge the support of

management of Halliburton for the opportunity to present this

work. Special thanks are also due to Harold Walters, Billy

Slabaugh, Johnny JohnsolL and David Bamck for their

contributions to constructing the apparatus and implementing

the experimental work.

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HESI300398
6 SPE 95287

Table lmExample Effects of Fracture Geometry on Vol.-Avg. Shear Rate

Wf, in. hf=10 20ft 30ft 40ft 50ft 60ft

ft

0.1 4,436

0.2 1,109

0.3 493

0.4 277

0.5 177

0.6 123

0.8 69

1.0 44

Assumptions:

2,218 1,479 1,109 887 444

555 370 277 222 111

246 164 123 99 49

139 92 69 55 28

89 59 44 35 18

62 41 31 25 12

35 23 17 14 7

22 15 11 9 4

Wellbore flow rate = 35 bbl/min

Average leakoff rate = 50%

hf = average vertical height of fracture,

wf = average width of fracture, in.

0.1 230

0.2 115

0.3 77

0.4 58

0.5 46

Assumptions:

Table 2mRatio of Horizontal to Ve~ical Velocity in Fracture

Wf, in. hf=10 20 ~ 30 ~ 50 ~

115 77 46

58 38 23

38 26 15

29 19 12

23 15 9

Wellbore flow rate = 35 bbl/min

Average leakoff rate = 50%

Particle size, microns = 500 (20/40 sand)

Newtonian viscosity, cP = 500

Table 3~Range of Conditions for Computing Viscosity of Fracturing SlurriesTM

Particle size 250 to 1,020 microns

Particle density 1.13 to 3.6 gm/cc

Sphericity 0.7 to 0.95

Power-law consistency 950 to 17,000 mPacoefficients secn

Shear thinning index 0.2 to 1.0

Volume fractions of particles 0.0 to 0.55

HESI300399
SPE 95287 7

1.00E+06

1,00E+05

1.00E+04

1.00E+03

1.00E÷02

1.00E+01

1.00E+00

0.01

Dilute Range

Single Particle

VAV = f(C~) Random

Bump,ins and

Colliding -

VAV = f(C~)

: :

Constant

siidin~touching

/crowding

VAV : f(C’ ~)

;

;

:

:

;

;

:

:

0.1

Particle Concentration, v/v

Fig. 1--Effect of particle concentration on fluid viscosity.

Fig. 2--Diagram of proppant viscometer.17

HESI300400
8 SPE 95287

40,000

o

0

O~

30,000

20,000

10,000

40 lb/Mgal 1 O0 Ib/Mgal

0

Time, min

Fig. 3a--Proppant settling in noncrosslinked base-gel fluids.

6,000

5,000

4,000

3,000

2,000

1,ooo

20 40 60 80 100

Polymer Concentration, Ib/Mgal

Fig. 3b--Rate of viscous settling slopes computed from Fig. 3a.

120

HESI300401
SPE 95287 9

50,000

40,000

30,000

~

" 20,000

10,000

o

0:00

Temperature

Model 50 Viscous

’~ ~Viscosity ~effling Region

400 cP Ref Viscosity ~-" ~-~ ~ ~ ___

Elastic Sand Transport

X~.~ of Sand Settling

Sand Transport

1:00 2:00 3:00 4::00

Test time, hr

Fig. 4--Response of a viscoelastic crosslinked slurry with breaker.

250

30,000

20,000

35

Fig. 5--Transport visualization with metal crosslink fluid with enzyme breaker.

HESI300402
10 SPE 95287

40,000 300

30,000

20,000

10,000

Temperature

25 Ib/Mgal

30 Ib/Mgal

Viscous Settling

of Sand Settling

50 100 150 200

Time, min

Fig. 6a--Effect of polymer concentration in metal-crosslinked fluid.

250

20O

5O

0

25o

800

~ 600

~

500

~ 400

oO

300

1oo

Polymer Concentration of Metal Crosslink Fluid, Ib/Mgal

Fig. 6b--Rate of viscous settling as affected by gel loading.

HESI300403
SPE 95287 11

50,000, 300

40,000,

30,000.

20,000.

10,000.

5gaVMgal

Breaker

Temperature

.... ......

o o o 1~o

Time, min

Fig. 7a--Effect of breaker concentration on metal-crosslinked fluid.

250

200

150

10o

5o

15,000

5,000

:::::::::::::::::::::::::::::

:::::::::::::::::::::::::::::

:::::::::::::::::::::::::::::

0 1 2 3 4 5

Breaker Concentration, Cb (gal/Mgal)

Fig. 7b--Rate of viscous settling as affected by breaker content.

HESI300404
12 SPE 95287

50,000 3O0

40,000

~ 3o,ooo

>~," 20,000

10,000

pH 7

0

~o ~o ~o ~o ~.~o 3oo

Time, min

Fig. 8--Effect of acid hydrolysis on crosslinked polymer.

250

200 ou-

 ̄ ~5o ~

8.

E

100

5O

60,000

50,000

40,000

30,000

20,000

10,000

25 Ib/Mgal

..... p.r£ppa£t .... Deposited

Proppant

Transported

Time, min

3OO

Fig. 9--Transport with borate crossliked fluids at 100°F.

HESI300405