spacer fluids properties.pdf

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Technical Bulletin

Kelco Oil Field Group 10920 W. Sam Houston Pkwy North, Ste 800 Houston, TX 77064 (713) 895-7575

www.kofg.com

Xanthan Gum in Oil Field Spacer Fluids

Spacer Fluid Applications

Spacer fluids are used in the oil industry to displaceand separate different fluids in a wellbore. Theirpurpose is to minimize the contact or mixing of thetwo fluids. These applications include:

Separating cement from drilling fluids.

Displacing drilling fluids with brine waters.

Separating oil-based drilling fluids fromwater-based drilling fluids.

Recovering expensive oil-based fluidsand brine waters.

Preventing dilution of chemical treatingsolutions.

KELZAN

XCD and XANVIS

are useful in thevarious spacer fluids because of their uniquerheological properties. The pseudoplasticity (highviscosity at low shear rates and low viscosity athigh shear rates) of these polymers provides ahigh annular viscosity for optimum displacement

efficiency.

Considerable experimental and field-work havebeen done investigating the displacement of onefluid by another, primarily in cementing operations.The principles and fluid properties found desirableduring these tests will normally apply to all fluiddisplacements. It was found that under mostcircumstances turbulent flow has the highestdisplacement efficiency due to its scouring effectat the wellbore and pipe surfaces. However, ithas also been established in most drilling,workover, and completion operations, thatoptimum suspension properties are achievedunder laminar flow conditions. Turbulent flowacross the annulus is generally not possiblebecause of normal pump limitations and pipeeccentricity, exceeding formation breakdownpressure, hole erosion and other considerations.

The unique rheological properties of xanthan gumfluids offer two key functions. First, they shear thinat the wall, providing a desirable scouring effect.Second, they provide superior suspension capabi-lities toward the center of the flow stream wherethe shear rate is substantially lower

Spacer Fluid Rheology

For optimum displacement efficiency, the effectiveannular viscosity of the spacer fluid should begreater than the fluid in the hole. To determine thebest spacer fluid viscosity, the viscosity of the fluidin the hole can be measured by an appropriateinstrument such as a variable speed viscometer.

Another method is to compare the "K" value fromthe Power Law model as calculated from the sameinstrument. Since the "K" value is the viscosity ofthe fluid at one sec

1shear rate, keeping the "K"

value of the spacer fluid higher than that of the fluidto be displaced will normally ensure a good disp-lacement. Kelco Oil Field Group technical bulletin,

Drilling Fluid Rheology -"n" and "K" applications'describe the procedure for determining the "n" and"K" values.

Spacer fluid efficiency is also improved by main-taining a low "n" value from the Power Law model,coupled with high viscosity at shear rates below10 sec

-1. These features are readily achieved by

formulating a spacer fluid with 1.5 - 2.5 lb/bbl ofKELZAN XC, XCD, orXANVIS. The net effect is aflatter velocity profile with a distinct low shear rateregion, which allows enhanced carrying capacity inthe center of the flow stream. This results in cleanerfluid displacements and the efficient transport of

debris being removed.


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Technical Bulletin

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Figure 1. Annular Flow Profile of a KELZAN

XCD or XANVIS

Formulated, Low n ValueSpacer Fluid, Illustrating Carrying Capacity

High

Shear Rate

Ref: SPE 26329

SPE 25767

SPE 22066

Region ofRegion of

Low Shear RateLow Shear Rate

High Viscosity,High Viscosity,

solidssolids

High

Shear Rate

Ref: SPE 26329

SPE 25767

SPE 22066

Region ofRegion of



Region ofRegion of



solidssolidssolidssolids

Figure 2. Viscosity vs Shear Rate of KELZAN XCD in 2% KCl@125F

0 0.1 1 10 100 1,000

Shear Rate, sec-1

1

10

100

1,000

10,000

Viscosity,

cP

0.75 lb/bbl

1.0 lb/bbl

1.5 lb/bbl

0 0.1 1 10 100 1,000

Shear Rate, sec-1

1

10

100

1,000

10,000

Viscosity,

cP

0.75 lb/bbl

1.0 lb/bbl

1.5 lb/bbl


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Technical Bulletin

KELZANand XANVIS

are registered trademarks of CP Kelco U.S., Inc. and may be registered or applied for in other countries.

2001 CP Kelco U.S., Inc.The information contained herein is, to our best knowledge, true and accurate, but all recommendations or suggestions are made without guarantee, since we canneither anticipate nor control the different conditions under which this information and our products are used. It is our policy, to assist our customers and to help in

the solution of particular problems, which may arise in connection with application of our products.Rev. 09/05

Additional features ofKELZAN

XCD and XANVIS

spacer fluids:

High annular viscosities Suspend weighting agents (9.0 to 20 lb/gal) Compatible with most salt solutions Not affected by drilling and work-over fluids generally being displaced Good temperature and pH stability Provide more friction reduction in tubulars More shear stable than cellulosics

Spacer Fluid Design

1. Determine the viscosity and "n" and "K" values of the fluid in the hole. Calculate the flow properties,plastic viscosity, and yield point. Also measure gel strengths and density.

2. Spacer Fluid Properties:

- unweighted fluids 0.25 - 0.4"n" value

- weighted fluids 0.35 - 0.4

"K" value - greater than the fluid in the hole

Plastic Viscosity - less than the fluid in the hole

Yield Point - greater than the fluid in the hole

3 rpm reading - greater than the fluid in the hole

Density - intermediate between the fluid in the hole and the displacing fluid.

Adjust spacer fluid flow properties by varying amount of xanthan gum. Use weight material or dissolvedsalts for density.

Table 1Suggested Parameters for Fluid Design

Well Fluid Spacer Fluid* Displacing Fluid

"n" Value

"K", dynes-secn/cm

2

PV, cP

YP, lb/100 ft2

3 rpm reading

Density, lb/gal

0.55

6.3

23

14

3

11.6

0.24

33

9

20

10

10.5

0.9

0.2

7

1

0.5

9.0

*Ingredients: sea water, 1.5 Ib/bbl KELZAN XCD, 115 lb/bbl barite.

n and K calculated between 3 and 300 rpm.

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