### 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 performanceobtained 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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## STIMULATION TECHNOLOGY REVIEW

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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## HESI301710Melting 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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## STIMULATION TECHNOLOGY REVIEW

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 II



## ~ 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 carbonchain 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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## HESI301712

### 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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## STIMULATION TECHNOLOGY REVIEW

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