INTRODUCTION

Paraffin and asphaltene deposits

have plagued operators for years.

Mechanical devices such as scrapers

and knives are commonly used to

remove the deposits. Hot oiling is

another approach to relieving the

problem but can sometimes damage

the well. Additionally, chemical

dispersants are often employed to

aid in the cleanup. Solvents provide

the most effective means of removal,

with xylenes and xylene bottoms

having been the solvents of choice

for many years. However, recent

concerns about the environment

and personnel safety have prompted

operators to look for alternatives.

This article discusses two products

that Halliburton has developed that

address both of these concerns

without sacrificing the performance

obtained from xylene or xylenecontaining solvents.

PARAFFIN PRECIPITATION

Most crudes contain paraffin in

suspension, some more than others.

While the "light ends" generated

at the beginning of production may

hinder paraffin precipitation, this

tendency diminishes as production

continues. Some crudes are

particularly waxy, and temperature

changes can cause the paraffins to

precipitate. For example, cold

treating fluids contacting warm

formation fluids can cause paraffin

precipitation. Production passing

from a higher-temperature zone into

a lower-temperature one is also a

frequent cause.

Changes in pressure can also cause

significant temperature alterations

that affect the solubility of paraffin

in crudes. One example is the large

pressure drop between normal

formation pressures and the

pressure at the bottom of the well.

This has the effect of cooling the oil

substantially right at the formation

face, where paraffin development

causes major production problems.

Also, paraffin clings more easily to

rough surfaces (like a pipe wall)

than smooth ones. A slow-moving

film of oil will allow more time for

paraffin precipitation.

Although the cause of paraffin

deposits vary, the result is always

the same: a decrease in production

as buildups develop in the wellbore

and feed lines, sometimes to the

point that production even stops.

These deposits can also affect

equipment, often causing extensive

mechanical problems in rods,

pumps, tubing, and other systems.

ENVIRONMENTAL

CONSIDERATIONS

A range of different products and

techniques for bringing paraffin

problems under control is available.

The use of specially developed

solvents has become enormously

popular for the control and removal

of these organic deposits.

Increasingly, however, environmental

concerns have also become

involved in the effort to control

paraffin. Most of the solvents that

have become so popular in the field

Environ.

mentally

Friendly

Chemicals

Technical

Contributor:

William G, F, Ford

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Figure 1 A Fourier-transform infrared analyzer determined

the paraffin content of 14 waxes, designated W1, W2 ..... and

W14. The analysis indicated that waxes W3, W12, and W13

contained primarily heavy paraffins. Waxes W1, W2, W4, W5,

W6, W7, W8, and W10 were primarily heavy paraffins with a

small amount of water. Waxes W9 and Wll were primarily

heavy paraffins with a small to moderate amount of water.

Wax W7 was primarily heavy paraffins with a moderate to

large amount of water. No evidence indicated the presence of

asphaltenes in any of the waxes.

contain compounds that pose other difficulties

relating to transportation, handling, and disposal.

These considerations become especially acute in

offshore applications. Xylene, for years considered

to be the superior paraffin solvent available to the

petroleum industry, has recently come under the

scrutiny of various regulatory agencies. This chemical

has a flash point less than 75°F, which is below the

IO0°F minimum required for offshore operations.

More generally, solvents with benzene, ethyl benzene,

toluene, and xylene (BETX) are encountering resistance

among environmentally conscious operators seeking

effective alternatives. They desire an environmentally

friendly solvent, a term that may have different

meanings. Some operators consider environmentally

friendly solvents to be those that contain no

benzene, ethyl benzene, xylene, or toluene. Other

operators require the solvents to contain no more

than 1% of aromatics of any kind. Still others

require various amounts of different types of

aromatics in the 25% to 75% range. No matter

what the composition of the solvents, all customers

would like the solvents to perform as well as xylene

and at approximately the same cost.

SEEKING SOLUTIONS

Halliburton sought to develop paraffin solvents that

were environmentally friendly and that were

comparable in paraffin dissolution to xylene and

other commercially available paraffin solvents. The

new solvents would contain no BETX compounds,

have an aromatic content that would satisfy various

clients’ needs, and have desirably high flash points

of 115°F or higher.

To evaluate the solvents that were developed, 14

waxes were obtained from field operations. The

waxes were first analyzed for paraffin content,

melting point range, and carbon chain length

distribution, and were then used in solubility tests.

Paraffin and Solids Content of

Evaluated Wax Samples

Wl

w2

w3

w4

w5

w6

w7

w8

w9

WlO

Wll

w12

w13

w14

,, ,, ,, ,, ,,

0 10 20 30 40 50 60 70

Content (%)

[] Solids [] Other

,, ,, ,,

80 90 100

] Paraffin

Figure 2 In the 14 wax samples that were analyzed,

total paraffin content ranged from 23.70% to 96.88%.

Three of the waxes contained no non-wax solids, while

the non-wax solids content of the remaining 11 waxes

ranged from 0.26% to 9.05%. The non-wax solids

content present in the waxes was too small to be

determined by x-ray diffraction analysis.

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Melting Point Ranges

Figure 3 A differential scanning calorimeter

determined the melting point ranges of the waxes.

Infrared analysis (Figure 1) revealed the waxes’

paraffin content, Figure 2 summarizes the results

and shows that there was wide variation in the

paraffin and solids content of the waxes,

Differential scanning calorimetry (Figure 3) found the

waxes’ melting point ranges. Figure 4 indicates that

the ranges of the majority of the waxes were very broad.

Gas chromatographic analysis (Figure 5) determined

the waxes’ carbon chain length distribution. The

results are depicted in Figure 6 and show that the

waxes exhibited a diversity of distributions.

Knowledge of this property is helpful in matching a

particular type of solvent to a particular paraffin to

achieve maximum dissolution. In particular, a

solvent’s KB (kauri butanol) value is matched with

the paraffin’s chain length distribution. The KB

classification and associated tests were devised by

the paint industry in the 1930’s to determine and

quantify the solvency of various materials.

Gravimetric solubility tests were performed with the

solvents and the 14 waxes. In these tests, specific

amounts of wax (by weight) and solvent (by volume)

were placed in ajar and were allowed to interact

for a designated amount of time. The jar’s contents

were then poured onto pre-weighed filter paper,

which was then oven-dried and weighed again.

From the recorded weights, the amount of wax that

was dissolved was determined.

Wl

w2

w3

w4

w5

W6

~ w~

x W8

W9

W]O

W]]

W]2

W]3

W]4

I I I I I

50 100 150 200 250

Temperature (°F)

Figure 4

several of the waxes. For example, waxes W1, W4, W6, W9,

WIO, and W13 had ranges of 85°F or greater.

The melting point ranges were very broad for

Figure 5 The carbon chain length distribution of each wax

was found with a gas chromatograph.

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Gas Chromatographic Analysis Sol ubility

Wl

w2

w3

w4

w5

W6

~- w7

x w8

w9

WlO

Wll

w12

w13

w14

m i i i

i I I I

~I I II

II I I I

~ I I

Iml I I I

ml i II

0 20 40 60 80 100

Carbon Chain Length Distribution (%)

D <C18 D C31- C40 D C51- C60

[] C18- C30 [] C41 - C50 [] C61 - C70

Figure 6 The wax samples represented a wide cross section

of carbon chain length distributions. Paraffins with carbon

chain lengths less than 31 are considered to be low-molecularweight paraffins, and those with lengths greater than 40 are

considered to be high-molecular-weight paraffins. Those with

chain lengths between 31 and 40, inclusive, are generally

thought of as intermediate-molecular-weight paraffins.

Wl

w2

w3

w4

w5

w6

w7

w8

w9

WlO

Wll

w12

w13

w14

o.oo 0.05 0.10 0.15 0.20 0.25 0.30 0.35

Solubility (Ib wax/gal solvent)

Solvent A Solvent B Xylene

Figure 7 In general, the new solvents outperformed

reagent-grade xylene in solubility tests. In only three

cases (waxes W8, W13, and W14) was the solubility of

the wax higher in xylene than in both of the new solvents.

THE NEW SOLVENTS

Two new solvents, Solvent A and Solvent B, were

developed that met the proposed environmental

and performance criteria, Neither solvent contains

any BETX compounds, with Solvent A being 100%

aromatic and Solvent B being only 1% aromatic,

Solvent A has a tagged-closed-cup (TGG) flash point

of 150°F, while Solvent B has a TGG flash point of

120°F, In comparison, reagent-grade xylene has a

TGG flash point of less than 75°F, The high flash

points of the two solvents makes them and their

blends suitable for offshore use,

In the gravimetric solubility tests, the solvents performed

overall as well as or better than reagent-grade xylene.

See Figure 7. This good performance and the

compatibility of the two solvents allow clients to use

either solvent individually if either a very high or a

very low aromatic content is required, or to blend

the two if an intermediate aromatic/non-aromatic

ratio is needed.

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APPLICATIONS

Besides dissolving paraFFins, the new solvents have

other uses.

 ̄ They can be used to degrease a producing well

that will be placed on waterflood.

They serve as preflushes for scale removal. In

scale removal, it is desirable to use organic

solvents such as these to remove the oil deposits

from the face of the scale so that the scale

removal treatment will be more effective.

 ̄ They function as carriers for a surfactant used in

removing and preventing emulsions and waterblocks.

They act as carriers for a special waterless, oil-soluble

acid that helps break emulsions and waterblocks,

dissolves calcareous material, and prevents the

redeposition of iron dissolved from the formation.

 ̄ They are excellent carriers for paraffin inhibitors

used in a chemical placement treatment that

protects against paraffin deposition.

The two chemicals are specifically recommended

as the organic solvent phase of an acid dispersion

treatment, in which a surfactant and acid solution

are blended together with an organic solvent.

The solvent dissolves organic residues, while the

acid reacts to remove scale deposits or to increase

formation permeability.

 ̄ They are the solvents of choice when preparing a

certain treatment fluid used for removing invert

oil-base drilling muds.

ABOUT THE CONTRIBUTOR

William G.F. Ford is a Senior Chemist fl in the

Stimulations Chemicals section at Halliburton’s

Duncan Technology Center. He received his doctor

oF phflosophy degree in chemistry From Texas A&M

University and has worked For Hafliburton For 18

years. Dr. Ford holds more than a dozen patents and

has authored several papers in the area o1: chemical

stimulation. He was a Society o1: Petroleum Engineers

Distinguished Lecturer during 1985 and 1986. His

current areas oF interest are suffactants, solvents,

scale and paraFFin control, and pipe dope removal.

SUMMARY

Halliburton has developed two new paraffin solvents

that are environmentally friendly and that perform

as well as or better than xylene, the industry’s

former superior paraffin solvent. The solvents find

other application as degreasers and as oil-removing

preflushes. They are also important components in

treatment fluids that remove and prevent emulsions

and waterblocks, inhibit iron redeposition, protect

against paraffin deposition, and remove organic

residues and invert oil-base drilling muds.

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