Evaluation of Barium Sulfate Scale Inhibition using Relative

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Applied Chemistry

Evaluation of Barium Sulfate Scale Inhibition using Relative Permeability Modifier polymers as adsorption enhancer for mature offshore well treatments in Campos Basin, Brazil. Daniel Maffra, Tiago Cavalcante Freitas, Georgiana da Cruz, Fernando Diogo de Siqueira, and Francisca Rosário Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.8b01828 • Publication Date (Web): 01 Aug 2018 Downloaded from http://pubs.acs.org on August 10, 2018

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Industrial & Engineering Chemistry Research

Evaluation of Barium Sulfate Scale Inhibition using Relative Permeability Modifier polymers as adsorption enhancer for mature offshore well treatments in Campos Basin, Brazil. Daniel A. Maffra*,†, Tiago C. Freitas‡, Georgiana F. da Cruz*,†, Fernando D. de Siqueira†, Francisca F. do Rosário‡ †Laboratory of Petroleum Engineering and Exploration, North Fluminense State University – LENEP/UENF, Macaé, RJ, 27910-970, Brazil ‡ PETROBRAS/CENPES, Ilha do Fundão, Quadra 7, CEP 21949-900 Rio de Janeiro−RJ Keywords: Scale inhibitor, Relative Permeability Modifiers, Polyacrylamide, Adsorption, Porous media, Oilfield treatment

ABSTRACT. In many mature offshore fields, high water cuts and potential scale deposition are some of the toughest challenges operators need to face. Two common practices used to deal with these challenges are relative permeability modifiers (RPM) polymer injection and scale inhibitor squeeze treatments. Even though many fields face these two challenges simultaneously, little is

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known about concomitant application of these treatments. In this paper, the effect of applying RPM polymers prior to inhibitor squeeze in the effectiveness of the last treatment is evaluated for sandstone rocks of Campos Basin, Brazil. Sequential laboratory injections in Campos Basin rocks of commercial cationic and anionic polyacrylamide and polyaluminium chloride (PAC) as crosslinking agent were employed prior to the injection of a commercial organophosphonic acid type inhibitor for barium sulfate scale. It was found that the polymers employed are capable of reducing the permeability of porous media to water and increasing the retention time of the scale inhibitor simultaneously. The tests also indicated that the inhibitor’s longer retention time is associated with the interaction with an outer cationic layer of the crosslinking agent. The adsorption isotherms were calculated and compared with Langmuir, Freundlich, Sips and Toth models, the last two being the most accurate in representing the adsorption system for these tests.

INTRODUCTION The Campos basin, located on the northern coast of the state of Rio de Janeiro, Brazil, is one of the main oil producing regions in the country, having started its production activities in the early 1970s.1,2 Most of its fields are currently in a mature stage of production, registering an increase in the volume of produced water and, consequently, a decline in the Productivity Index (PI). In addition, many fields in the basin present problems associated with inorganic scale, causing further reduction of the wells productivity. Among different inorganic scales, barium sulfate is one of the most recurrent in the Campos basin.3,4 In order to minimize inorganic scale deposition, companies routinely resort to prevention treatments. This is often done in production wells via chemical inhibitors squeeze treatments, particularly where sulfate removal plants are not available at seawater injection facilities. These


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chemicals are adsorbed into the pores of the rock surface and are slowly released, ensuring well protection for months.5 Several studies have been carried out to improve the adsorption efficiency of scale inhibitors on the surface of reservoir rock pores, in which chemical additives were added to the treatment in order to promote greater interaction between the inhibitors and the surface. Calcium ion (Ca2+), for example, has been studied in several works6–11 for improving the adsorption of inhibitors as to the influence of their concentration, temperature and pH of the medium and synergy with other ions. Due to its function of prolonging the inhibitors' retention in the reservoir and its availability in many connate waters, calcium ion is considered to be one of the main additives used in offshore treatment. Some studies12–14 indicate that traces of transition metals, such as Zn, Cu and Fe, present in the formation water of some fields, can improve the adsorption efficiency of aminophosphonic acid inhibitors and can be potentiated with a pH adjustment. There are also studies investigating the use of carbon nanotubes to increase the adsorption efficiency of organic chemicals, which can be applied to increase the retention of chemical inhibitors in squeeze treatments.15,16 In addition to being the basis for some types of inhibitors, acrylamide-based polymers are also used to reduce water cuts, which are usually higher in mature fields. These polymers are able to adsorb in the porous medium and reduce relative permeability to water, and are therefore known as Relative Permeability Modifiers (RPM).17–33 Zaitoun et al.18,34 presented two methods of using RPM: through the application of hydrolyzed polyacrylamide, varying the salinity of the medium to obtain the viscosity of interest (polymer swelling method) in order to reduce water mobility, and another using non-ionic polyacrylamide and a swelling agent (potassium carbonate), to achieve an effect similar to the previous. Other studies have also used polyacrylamide in a


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microgel form in order to obtain greater control of the desired molecules volume and achieve a higher degree of permeability reduction.29,35,36

Barbosa et. al.37,38 developed a sequential

injection method of cationic polymer and anionic copolymer layers in which these layers are superimposed on the porous medium until reaching the desired degree of water permeability reduction. A crosslinking agent could also be employed after the injection of the anionic polymer layer. In view of the viability of chemical treatments use for the recovery and reestablishment of the wells PI, through chemical inhibitors and RPM polymers, some studies have been presented in the literature in which both treatments are used in combination.39,40 However, studies of inhibitor sorption onto previous polymeric multilayered surface within rock porous for field application as combined scale inhibition and water production control treatments are lacking in literature. Furthermore, synergetic effects of inhibition enhancement due to RPM polymers interaction with inhibitor molecules are still not completely understood. In this work, a preliminary and innovative approach is presented for squeeze treatment enhancement using a commercial scale inhibitor of barium sulfate in rock samples from mature fields of the Campos Basin, using commercial RPM polymers and PAC layers as additives to increase inhibition adsorption efficiency while still maintaining the function of water flow restraint agent. While RPM polymer and PAC layers primarily reduce water flow in rock porous, the desorption curves indicate that the outermost cationic layer has an important role in retaining the inhibitor molecules.

MATERIAL AND METHODS Chemicals


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The selected RPM polymers were chosen due to their resistance to temperature and pressure conditions similar to those found in the fields of interest in the Campos Basin. Among these polymers, two are anionic copolymers of polyacrylamide and polyacrylic acid, with hydrophilic linear chains, and a degree of hydrolysis ranging between 25-32%, while the third is a quaternary aliphatic polyamine cationic polymer with a charge density of 100% (CAT1). Anionic polymers differ in terms of the presentation of the original material and the amount of active matter, one being in powder and the other in emulsion. Table 1 presents more detailed information, provided by the products manufacturer, on each polymer used. Polymer solutions were prepared according to the procedures of API Recommended Practice 63,41 in which the original, pure product is diluted under agitation to generate a stock solution at a concentration of 5000 ppm. All polymer stock solutions were subsequently diluted with 2% KCl water to 1000 ppm polymer concentration, which were used in the static and coreflood tests. Table 1. General information of the polymers used in the tests. POLYMER CHARACTERISTICS RPM1

RPM2

CAT1

Form as received

Suspension

Granular solids

Liquid

Polymeric solution color

Milky/white

Translucent

Light yellow

Ionic character

Anionic

Anionic

Cationic

Density of charge

28% to 32%

25% to 30%

100%

Molecular Weight (Da)

11.5×106 to 16.5×106

7.5×106 to 11×106

104 to 106

Viscosity (cP)*

13.00

5.40

1.07

Active matter

30%

87%

40%

*1000 ppm solution at 23⁰C and 1atm


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A crosslinking agent was also used after injection of the anionic polymers to promote interand intramolecular crosslinks between polymer molecules and thus increase the fixation and duration of treatment under more severe reservoir conditions. The crosslinking agent is a waterbased solution of Polyaluminium Chloride (PAC), of molecular formula Al2(OH nCl(6-n))m where m is the degree of polymerization (m

Evaluation of Barium Sulfate Scale Inhibition using Relative

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