XIX International Gas Convention AVPG 2010, May 24th - 26th Caracas, Venezuela

GREEN CHEMISTRY FOR TREATMENT OF SCALING *Elluz Torín, Luis Castillo, María Carrasquero and Alfredo Viloria Gas Technical Management, PDVSA Intevep, Telephone: 0212 3307730, Fax: 0212-3308730. Apdo 76343, Caracas 1070-A, Venezuela E-mail: [email protected]

ABSTRACT

The scale is one of the most important problems of oil and natural gas. This phenomenon could compromise the integrity and shelf life of producing wells and injectors, surface facilities, pipeline production, transmission and distribution lines, and pipelines in general, resulting in large expenditures for the industry. New developments of chemical treatments to mitigate the scales of the hydrocarbon industry are focused towards the use of green chemistry, due to the enormous benefits it entails, opening up new branches of research. Green chemistry is the use of techniques and methodologies that reduce or eliminate the generation of contaminants, and can potentially find many applications in the treatment of water associated with hydrocarbon exploitation, specifically to combat the scales phenomenon. Conventional technologies used to combat them are based primarily on the use of condensed phosphates, polyfosfonates, polycarboxylic, among others, which can impact the environment and generate high costs for industry. In this regard, great efforts have joined in the development of a scale inhibitor based on Aloe vera, whose active ingredient is in the polysaccharides present in this plant. The product has shown high efficiency and stability in the case studies raised, and its performance often superior to conventional treatments. This technology is targeted with new trends of green chemical treatments, reducing pollution in the production activities because it is a completely biodegradable product, allowing the foreign exchange savings through import substitution and promoting technological independence.

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XIX International Gas Convention AVPG 2010, May 24th - 26th Caracas, Venezuela

INTRODUCTION

Hydrocarbon production is associated with a certain amount of water, known as produced water, which is saturated with minerals that are mostly native to the site, and give rise to the formation of scales. One of the major problems of exploitation of these resources is that, as the reservoir is exhausted will increase the amount of water in it, becoming more acute salt deposits.

This phenomenon is caused by fluids associated with hydrocarbon production, changes in the thermodynamics, kinetics and hydrodynamics under which these fluids are produced (Vetter 1976), or by incompatibility between formation fluids, and injection production, presented in various areas of the value chain of natural gas, compromising the integrity, good shelf life and facilities, resulting in increases in operating costs in the industry (Castillo 2005).

The methods employed by the oil industry are scale inhibitors, which interact with the crystals precipitated under different mechanisms, and are designed to prevent scale formation (Hasson et al. 1998). The development of these inhibitors requires knowledge of the factors that mainly affect the balance of the solution and the kinetics of precipitation (Neville and Morizot, 2000).

Conventional chemical treatments used in the mitigation of this phenomenon can be either organic or inorganic. The inorganic is mainly based on condensed phosphates such as polymetaphosphate or Dimetal phosphates, acting on the formation of the scale stunting the growth of crystals (Nowack 2003), while organic compounds (polyphosphates, polyfosfonates, polycarboxylic and polimeliatos) have a chelating effect on the ions that form the scale (Nowack 2003), Most of these products are made of synthetic chemicals, have high environmental impact because it is not biodegradable, and additionally require treatment prior to disposal.

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XIX International Gas Convention AVPG 2010, May 24th - 26th Caracas, Venezuela

Currently have been making great efforts in developing new formulations of antiscaling chemical treatments based on the statements of green chemistry. They provide efficiencies similar to conventional products, but with the advantage that pose no risk to the environment.

The role of green chemistry is closely related to the broad trends emerging in policies,

regulations

and

incentives,

industry

initiatives,

and

scientific

developments and professionals involved in the reinvention of new routes, using friendly materials environment to enable the replacement of polluting products. It represents an innovative alternative to combat pollution, being used in new formulations of the chemical treatments, aimed at securing the flow of the oil industry, thus preventing a variety of phenomena such as scale, hydrates and corrosion.

Based on the current issues facing the oil industry and based on these statements, PDVSA Intevep conceptualized the design, manufacture and application of a scale inhibitor based on Aloe vera, in order to maintain a balance between flow assurance operations and the environment. A new concept: natural biopolymer scale inhibition, INTAVTM

The conceptualization of the use of Aloe vera as an scale inhibitor arises in the search for natural products and processes, framed within the principles of green chemistry, where possible employing raw materials from multicellular organisms like plants. This product is called INTAVTM and its aims that reduced use of hazardous reagents that may cause damage to the environment accordingly.

The active ingredient in this inhibitor is found in the polysaccharides present in the plant, which uses the extremophile nature of Aloe vera in harsh environments associated with high temperature and pH, as well as showing affinity natural polysaccharides by water, incorporating strongly in biological structure. This plant is mainly composed of sugar molecules such as glucose, O-acetylmanose and galactose, which are linked into chains either short, long or very long (Danhof

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XIX International Gas Convention AVPG 2010, May 24th - 26th Caracas, Venezuela

2009). The proposed structure of the polysaccharides present in Aloe vera gel is shown in Figure 1.

Figure 1. Proposed structure for the main component of polysaccharides from Aloe vera gel (Danhof 2009)

The mechanism of inhibition that best describes this phenomenon represents a model of the box egg. This model consists of polysaccharide molecules that interact with divalent cations, forming bridges between two carboxyl groups belonging to the OAcManosa acetyl groups from two different chains in close contact (Iain 1989) (Figure 2).

Figure 2. Inhibition Model Egg Box (Viloria 2007)

The model proposed requires the cooperative binding of two or more chains of polysaccharide (Diaz et al. 2007). While calcium ions help to keep the molecules together, their polymeric nature and their aggregation more strongly bind calcium, which is commonly called cooperative binding, which are responsible for the conjunction of all these families of compounds present in the gel and is presumed that have a synergistic effect (Li et al. 2007).

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XIX International Gas Convention AVPG 2010, May 24th - 26th Caracas, Venezuela

EXPERIMENTAL METHODOLOGY

Trials assessing the efficiency of scale inhibitors at laboratory scale are performed in a static state in glass cells, following the procedure specified in the standard NACE TM0374 (NACE International 2001). In these experiments used synthetic mixtures of water whose chemical composition is established by the standard and to evaluate inhibitors. The test lasts for 24 hours at a temperature of 71 ° C and atmospheric pressure.

The bench-scale assessment is done again in a static state, using equipment called autoclaves, which simulate the operational parameters of pressure and temperature of the real system under controlled conditions. This experience is conducted at a temperature of 132 °C and a pressure de13.8 MPa (Maximum pressure), under the NACE Standard TM0374, but produced water using the system under study.

The bench-scale assessment is done again in a static state, using equipment called autoclaves, which simulate the operational parameters of pressure and temperature of the real system under controlled conditions, this experiment is performed under the NACE Standard TM0374, with the difference that produced water is used the system under study. The equipment used in this study have a maximum pressure of 13.8 MPa.

RESULTS AND DISCUSSION

Validation of the concept on a laboratory scale and bench

Once identified the antiscaling potential of Aloe vera gel, was evaluated the performance of this product in laboratory scale, by efficiency testing under the NACE Standard TM0374. Similarly several conventional inhibitors were evaluated commonly applied within the oil industry (Figure 3).

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Efficiency (%)

XIX International Gas Convention AVPG 2010, May 24th - 26th Caracas, Venezuela

100 90 80 70 60 50 40 30 20 10 0

97

33,5

31,1 22,7

15,1

10,8 0,4

Aloe vera

Inh-1

Inh-2

Inh-3

Inh-4

Inh-5

Inh-6

Inhibitor

Figure 3. Efficiency of scale inhibitors tested in static conditions, under the standard NACE TM0374 May be evident in Figure 3 that the formulation based on Aloe vera gel (INTAVTM) has an efficiency of 97% inhibition, thus overcoming the values achieved with conventional inhibitors (from 0.4 to 33.5%). In this sense, this new product based on the statements of green chemistry as an alternative to alleviate the problem facing the oil industry by maintaining a balance between flow assurance and the environment

Once the laboratory scale test is passed to the next stage for bench-scale evaluation, using produced water from South Central Division Barinas. These tests were conducted at a temperature of 132 °C and a pressure of 13.8 MPa (Maximum pressure equipment). In Figure 4 show the results obtained using different doses of INTAVTM and a commercial product.

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Efficiency (%)

XIX International Gas Convention AVPG 2010, May 24th - 26th Caracas, Venezuela

100 90 80 70 60 50 40 30 20 10 0

100

93

93

5,25

97

10,5

95

25

Dose (ppm) Aloe vera

Commercial

Figure 4. Bench-scale assessment INTAVTM vs. commercial product The scale inhibitor based on natural polysaccharides (INTAVTM) once again showed highly satisfactory results, obtaining higher efficiency values than those obtained with commercial inhibitors. Already made the assessment stages of laboratory and bench scale, according to the excellent results with the product as evidenced INTAVTM, ran to the escalation of technology at field level.

Demonstration of technology: field tests in the South Central Division Barinas

Completed the testing laboratory and bench scales, the assessment was undertaken in the field in selected facilities in the South Central Division in Barinas state, according to its history of failures, presence of high temperatures, high percentages of water and sediment and high scaling tendency. The product evaluation was conducted field for 51 continuous days, and by the injection of the inhibitor to INTAVTM downhole.

The daily measurements of operational conditions of pressure and temperature were taken as standards for monitoring the test and visual inspection of the wellhead fortnightly. After the test was again removed the wellhead, being

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XIX International Gas Convention AVPG 2010, May 24th - 26th Caracas, Venezuela

completely free from solids scaling. Figure 5 presents the results obtained in this evaluation, which compares with the commercial product.

Commercial product

INTAVTM 20 days

INTAVTM 35 days

INTAVTM 51 days

Figure 5. Field Trial INTAVTM scaling inhibitor in South Central Division

At the beginning of the evaluation of product based on natural polysaccharides, was conducted an inspection of the wellhead, which was receiving a chemical treatment commercial, where it could be seen that the pipeline was with great amount of solids adhering to the surface, thereby causing throttling the flow in the well. Thereafter, the solids were analyzed, finding that they consisted mainly of CaCO3 (Figure 5). Initiated the implementation of INTAVTM inhibitor, was made the wellhead inspection at 20, 35 and 51 days, observing at all times that the pipe was free of scaling (Figure 5). The results yielded a high efficiency of the product, with excellent results compared to those evidenced with the commercial inhibitor used in the well.

Throughout the field test, production water samples were taken to determine the variation of calcium concentration in the system. Because through product inhibition mechanism, the polysaccharide chains retain divalent cations Ca+2, and keeping them in solution thereby preventing precipitation. Due this is expected during the implementation of INTAVTM, the concentration of calcium in the system will increase.

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XIX International Gas Convention AVPG 2010, May 24th - 26th Caracas, Venezuela

Figure 6 presents the results of monitoring the concentration of calcium in the evaluated system, taking as initial calcium concentration in the produced water before applying the product. It also shows the behavior of the pressure head

1000

400

900

350

800 300

700 600

250

500

200

400

150

300 200 100

Calcium Concentration

100

Pressure wellhead

50 0

24 .1 0 28 .1 0 01 .1 1 05 .1 1 09 .1 1 13 .1 1 17 .1 1 21 .1 1 25 .1 1 29 .1 1 03 .1 2 07 .1 2 11 .1 2

0

Pressure (Psig)

Calcium Concentratión (ppm)

during the 51 days of product application.

Date

Figure 6. Variation in calcium content in water production and pressure head during the field test During the escalation of technology scaling inhibitor INTAVTM, on the facilities of the oil industry, is apparent (Figure 6) that the calcium concentration in production water presented variations, showing a trend of increase, staying in a range of 681 and 886 ppm. This behavior could be associated with the retention of calcium ions as a result of the inhibitory action of the product, as noted in defining the mechanism of action of polysaccharides during the reaction.

Similarly, was tracked daily wellhead pressure resulting in a progressive increase of about 77 psig, which could be related to the presence of scaling solids that were in the downstream pipe before begin implementation of INTAVTM.

In any case, based on evidence that did not form solids in the wellhead, it is concluded that performance-based scale inhibitor Aloe vera gel is efficient,

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XIX International Gas Convention AVPG 2010, May 24th - 26th Caracas, Venezuela

because field experience has indicated that the lack of chemical treatment or their poor performance, the immediate causes scaling of the well installations.

CONCLUSIONS − In the laboratory-scale assessment and bench scale inhibitor INTAVTM presented 97% efficiency, yielding better results than conventional inhibitors (from 0.4 to 33.5%). − Inspection of the selected wellhead South Central Division, before starting the field test, confirmed the formation of calcium carbonate due to the commercial treatment applied. − The INTAVTM was efficient as an inhibitor of scale, and that the review at 21, 35 and 51 days of application in the selected well not found the presence of any solids. − The calcium concentration in production water presented variations, showing a tendency to increase, ranging between 681 and 886 ppm. − Product performance based on Aloe vera (INTAVTM) proved highly efficient for mitigating the scaling present in the oil industry.

REFERENCES

Castillo, L (2005). “Estudio de la factibilidad técnica de aplicación de biopolímeros y efecto de las nanopartículas en el tratamiento de incrustaciones y corrosión en la industria del gas”. Trabajo Especial de Grado. Universidad Central de Venezuela – PDVSA – Intevep.

Danhof

I.,

Position

Statement

on

Polysaccharides.

Consultado

en

http://www.iasc.org/poly.html el 08/09/2009.

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Díaz, E.; Villarán, M.; Río, F.; Ramírez, C.; Lorenzo, L. (2007). “Utilización de Adsorbentes basados en Quitosano y Alginato sódico para la eliminación de iones metálicos: Cu+2, Pb+2, Cr+3 y Co+2”. Revista Iberoamericana de Polímeros. Vol. 8, N°1.

Hasson, D.; Semiat, R.; Bramson, D.; Busch, M.; Limoni-Relis, B. (1998). “Suppression of CaCO3 scale deposition by anti-scalants”. Desalination. Vol. 118.

Lain C. M. (1989). “Industrial Polisaccharides”. Pure & Appl. Chem. Vol 61, N° 7. Pp 1315-1322.

Li, L.; Fang, Y.; Vreeker, R.; Appelqvist, I. (2007). “Reexaming the Egg-Box Model in Calcium - Alginate Gels with X-ray Diffraction”. Biomacromolecules. Vol. 8, N° 2.

Neville, A., y Morizot, A. (2000). “A combined bulk chemistry/electrochemical approach to study the precipitation, deposition and inhibition of CaCO3”. Chemical Engineering Science 55, pp. 4737-4743.

Nowack, B. (2003). “Environmental chemistry of phophonates”. Water Research. Vol. 37.

Vetter O. (1976). “Oilfield Scale – Can We Handle It?”. Journal of Petroleum Technology. Vol. 28, Nro 12.

Viloria, A., Inventor; Castillo L., Inventor; García J., Inventor; Biomorgi, J., Inventor (2007). Intevep, S.A., beneficiario. “Aloe derived Scale Inhibitor”. Estados Unidos, patente N° US 2007/0281866 A1.

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