DEVELOPMENT OF A PHOSPHONATE BASED NANOFLUID FOR THE INHIBITION OF CALCIUM CARBONATE PRECIPITATION

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1 DEVELOPMENT OF A PHOSPHONATE BASED NANOFLUID FOR THE INHIBITION OF CALCIUM CARBONATE PRECIPITATION DESARROLLO DE UN NANOFLUIDO BASE FOSFONATO PARA LA INHIBICIÓN DE LA PRECIPITACIÓN DE CARBONATO DE CALCIO MARIBEL FRANCO AGUIRRE Ingeniera Química, Universidad Nacional de Colombia, mfrancoag@unal.edu.co ABSTRACT: The oil wells productivity is affected by inorganic scales, they have an impact on the permeability and porosity, and cause a blocking of the formation matrix. Moreover, they impede the operation of equipment, deteriorate the pipelines, valves, pumps and they have a negative impact on the production fluids. In this sense, this study was done with the aim of developing a phosphonate based nanofluid, with the capacity to inhibit and remediate the calcium carbonate precipitation, in non-conventional reservoirs type tight. The effect of phosphonate concentration as reactive in the nanofluid synthesis was assessed. In order to evaluate the inhibition efficiency of the nanofluid, tests in static conditions were carried out. Likewise, tests in well conditions were performed to determinate the optimal concentration and the effect of the treatment on the permeability of the system, in the inhibition/remediation phases. The results, showed a nanofluid composed by 50 ppm of nanoparticles Ca-DTPMP plus 10% of synthetic fluid, with an efficiency of 72.7% in the calcium carbonate inhibition precipitation to static conditions; and to dynamic conditions was found the same concentration as the optimal concentration that caused less damage generation, corresponding to 1%. The nanofluid inhibits the damage generation due to scales deposition and it avoids the effective oil and water permeability declines of the system. In the remediation step, a damage of 75% in the system was generated, however the nanofluid had the capacity to remove the scales. In the case of oil, the decreasing in the permeability was exceeded and the oil permeability had an increasing of 57% in contrast with base permeability for tight reservoirs. In general the nanofluid improving the flow conditions of water and oil. KEYWORDS: Calcium carbonate, phosphonate, inhibition, nanofluid, remediation. 1. INTRODUCTION Scale formation and precipitation or inorganic encrustations, especially of CaCO 3 represent serious problems in many industrial processes [1-5], mainly related with mineral precipitation from water processes [2-8]. The inorganic scales can appear as a result of the mixture of two incompatible waters or pressure/temperature changes, etc. [1, 9-12]. Therefore, some consequences associated with scaling are: lowering heat transfer efficiency, total or partial blocking water flow and subsequently increasing pumping costs, also increasing the requirement for system cleaning [13]. Sometimes, the mineral scale can limit the oil and gas production by plugging formation matrix as well as fractures and perforated intervals, causing many problems such as formation damage, production losses, increasing work over in producers and injectors wells and also can decrease the quality of the injected water [14]. In this way, the CaCO 3 scaling from salt precipitation and its inhibition in the bulk of the solution, have been well studied, since it represents an important economic impact due to its relationship with several industrial processes such as oil production and water desalination [15]. Therefore, it is important to mention that now there is a major challenge that is looking for an improvement in the scale deposition control processes, which means in economic terms, the use of an effective inhibitor treatment. In this way, a

2 ESCUELA DE VERANO 2017 widely and effective technique used for controlling the scaling problems is the dosage of chemical additives able to weaken its adherence to surface [16]. Some examples of the types of inhibitors employed are phosphonates, that are compounds used extensively to delay and to inhibit scale formation of calcite [6, 10, 20-23] and belonging to the group of inhibitors threshold effect [1, 6, 10, 20, 21]. Phosphonates are strongly adsorbed on the active sites of the growing crystals, disrupting and slowing growth patterns, causing a major distortion and instability in the growing crystal matrix [1, 6, 11, 20, 24]. The synergistic effect of nanoparticles and synthetic fluid is the novelty of this work, which permits that the synthesized nanofluid inhibits and remediates the formation damage due to inorganic scales deposition. 2. EXPERIMENTAL 2.1. Materials Diethylenetriamine penta methylene phosphonic acid (DTPMP), was obtained from Sigma Aldrich as a 50% (w/w) solution. Other chemicals used were N-hexadecyl-trimethyl ammonium bromide (CTAB), sodium chloride (NaCl, 99.5%, Merck KGaA, Germany), calcium chloride dihydrate (CaCl 2 * 2H 2O, 99%, Merck KGaA, Germany) and sodium bicarbonate (NaHCO 3, 99.7%, Merck KGaA, Germany), these were of analytical grade and they were used without further purification Preparation of nanofluid Metal phosphonate particles of Ca-DTPMP were synthesized following the protocol described by Kiaei and Haghtalab [13, 23]. It is prepared a solution of CaCl 2 at 0.75 M, then 1.5 g of the surfactant CTAB are added; this mixture is continuously stirred at 350 rpm until a clear solution of ph 5.6 is formed. Subsequently, a solution of phosphonate at concentration of 0.3 M and with ph of 9.0 is prepared, this solution is added dropwise to the above solution, and it is leaving under moderate stirring for 1 hour. From this mixture was obtained a milky white precipitate, which was placed in a water bath at 80 C for 12 hours. After that, the sample was filtered on a filter paper (2-3 µm), the obtained product is dried at 100 C for 12 hours. For the synthesis of the metal particles of Ca-DTPMP at 0.01, 0.05, 0.1, 0.2 and 0.5M were used the same procedure described above. The nanofluids were prepare as follows: A specific concentration of particles Ca-DTPMP was taken and an amount of synthetic fluid was added, this fluid is obtained in the particles synthesis as was described above, in the filtration step. Calcium chloride brine was added to the vessel and was sonicated for 1 hour to ensure complete dispersion of the particles in solution Inhibition / precipitation experiments The inhibition/ precipitation experiments were made based on the methodology proposed by [13]. In each experimental test, 50 ml of de solution of CaCl 2 * 2H 2O (0.08 M) were added to the vessel, then the required amount of the particles was added and was sonicated for 30 minutes to ensure complete dispersion of the particles in solution. Subsequently, 50 ml of NaHCO 3 solution (0.08 M) was added. The test temperature was 70 C. The ability to inhibit the formation of CaCO 3 was obtained measuring Ca 2 + that remained in solution in the synthetic brine. For that purpose, the Ca 2 + was indirectly measured using a titration with EDTA (0.01 M). Inhibition efficiency for particles synthesized was determined by percent inhibition according to Equation 1 [13]. Ca Cb % Inhibition x100 C C c b (1)

3 18 ESCUELA DE VERANO 2017 Where C a the concentration of Ca 2 + in the treated sample after precipitation, Ca 2 + in the blank after precipitation and 2.4. Core displacement tests C c C b is the concentration of is the concentration of Ca 2 + in blank before precipitation. The core-flooding tests were performed at typical reservoir conditions of a temperature of 110 C (230 ºF) and confining and pore pressures of MPa (5000 Psi) and 6.89 MPa (1000 Psi), respectively. In this step, optimal nanofluid concentration was determined, after that, nanofluid was evaluated in inhibition/remediation phases. Figure 1 shows a schematic representation of the experimental setup. Figure 1. Schematic diagram of the core flood test: 1) oven, 2) the positive displacement pump, 3) displacement cylinders, 4) the filters, 5) electric hydraulic pump, 6) the core holder, 7) the pressure multiplier, 8) the back pressure system, 9) a valve, 10) the manometer, 11) the differential pressure meter and 12) the graduated cylinder. 3. RESULTS The Table 1 resumes the inhibition efficiency to two periods of time, 2.5 and 24 hours. The nanofluid that was prepared with 50 ppm (particles of Ca-DTPMP that were synthesized with 0.3M of DTPMP) and 10% of synthetic fluid presented the best inhibition efficiency. Nanofluids of Ca- DTPMP Table 1. Inhibition efficiencies of nanofluids of Ca-DTPMP. Concentration of Nanofluid (ppm of particles of Ca-DTPMP + % of synthetic fluid) Inhibition efficiency (%) 2.5 hours Inhibition efficiency (%) 24 hours The Figure 2 shows the highly distorted crystals of calcium carbonate, this indicates that particles of Ca- DTPMP were adsorbed on the growth sites; therefore, the growth pattern was altered.

ESCUELA DE VERANO 2017 a b Figure 2. SEM image of calcium carbonate crystals with the effect of nanofluid of Ca-DTPMP, a) blank calcium carbonate b) nanofluid of Ca-DTPMP 0.3M of DTPMP. 3.

Table 2. Properties of the sandstone core used in the coreflooding test. Property Value Length (cm) 7.05 Diameter (cm) 3.80 Porosity (%) 6.40 Absolute Permeability (md) 34.

4 ESCUELA DE VERANO 2017 a b Figure 2. SEM image of calcium carbonate crystals with the effect of nanofluid of Ca-DTPMP, a) blank calcium carbonate b) nanofluid of Ca-DTPMP 0.3M of DTPMP. 3.1 Core displacement tests Petrophysical properties of the sample, such as absolute permeability (Kabs) and porosity were evaluated, and summarized in Table 2. Table 2. Properties of the sandstone core used in the coreflooding test. Property Value Length (cm) 7.05 Diameter (cm) 3.80 Porosity (%) 6.40 Absolute Permeability (md) The decline of the absolute permeability was evaluated with the aim of find the optimal concentration with smaller damage percent by calcium carbonate precipitation. As was seen in the Table 3, the nanofluid composed of 50 ppm + 10 % presented the less damage percent, therefore that concentration will be evaluated in the inhibition/remediation phases. Concentration of Nanofluid (ppm of particles of Ca-DTPMP + % of synthetic fluid) Table 3. Optimal concentration of nanofluid. Absolute permeability K abs(md) Absolute damage permeability K abs(md) %Damage 50 ppm + 10% Inhibition It s important highlight that in the inhibition step were injected 60 PV of problem brine, and the nanofluid presented an excellence capability to inhibit the damage due to the calcium carbonate precipitation, additionally the nanofluid avoided the strong falls in the effective oil permeability and it allowed the equilibrium conditions remained stables, as can be seen in the Table 4.

5 20 ESCUELA DE VERANO 2017 Table 4. Effective permeabilities of water and oil in the inhibition of calcium carbonate precipitation. Pore volumes injected of problem brine (CaCl 2 * 2H 2O and NaHCO 3) PV initial 10 PV 30 PV 60 PV K w(md) K o(md) Remediation It can be seen that the nanofluid had the capability to restore the conditions of system, for water the effective permeability was decreased in 75% with the damage generated, after of nanofluid application the water effective permeability showed an increase. In the case of oil, the effect of nanofluid produced a significant improvement, because the base permeability was 0.30 md and with the application of nanofluid the permeability increased to 0.52 md, it s an increase of 57%, with a positive effect on oil mobility. Table 5. Effective permeabilities of water and oil in the remediation of calcium carbonate precipitation. Pore volumes injected PV initial 10 PV problem brine 3 PV nanofluid K w(md) K o(md) Conclusions Nanofluids that were synthetized, based on phosphonate (DTPMP), have the capability to inhibit and remediate the calcium carbonate precipitation. The tests carried out at static conditions showed high efficiencies for the periods of time that were evaluated, additionally the SEM images allowed see the alterations in the morphology of calcium carbonate crystals, the size and growth velocity were decreased. The combination of particles of Ca-DTPMP more synthetic fluid to prepare nanofluids showed an excellence performance, specifically the nanofluid prepared with particles de Ca-DTPMP with 0.3M of DTPMP presented the best efficiencies, that results led to development of tests a high temperature and pressure. The inhibition showed a high perdurability of the nanofluid, 60 PV of problem brine were injected, and the systems conditions remained stables during the injection of 10 and 30 PV, for the last injection of 60 PV, the effective permeabilities decreased, with less impact for the oil. The results in the remediation step represent an important characteristic of the nanofluid, when the damage was generated the treatment had the capability to recover the properties of the system, the mobility of the oil was improved, even above the base condition.

6 ESCUELA DE VERANO 2017 REFERENCES [1] MacAdam, J. and S.A. Parsons, Calcium carbonate scale formation and control. Re/Views in Environmental Science & Bio/Technology, (2): p [2] Zhang, Y., et al., The kinetics of carbonate scaling application for the prediction of downhole carbonate scaling. Journal of Petroleum Science and Engineering, (2): p [3] Crabtree, M., et al., Fighting scale removal and prevention. Oilfield Review, (3): p [4] Oddo, J. and M. Tomson, Why scale forms in the oil field and methods to predict it. SPE Production & Facilities, (01): p [5] Chen, T., A. Neville, and M. Yuan, Calcium carbonate scale formation assessing the initial stages of precipitation and deposition. Journal of Petroleum Science and Engineering, (3): p [6] Abdel-Aal, N. and K. Sawada, Inhibition of adhesion and precipitation of CaCO 3 by aminopolyphosphonate. Journal of Crystal Growth, (1): p [7] Chen, T., A. Neville, and M. Yuan, Assessing the effect of Mg2+ on CaCO3 scale formation bulk precipitation and surface deposition. Journal of Crystal Growth, (1): p. e1341-e1347. [8] Xyla, A.G., J. Mikroyannidis, and P.G. Koutsoukos, The inhibition of calcium carbonate precipitation in aqueous media by organophosphorus compounds. Journal of colloid and interface science, (2): p [9] He, S., A.T. Kan, and M.B. Tomson, Inhibition of calcium carbonate precipitation in NaCl brines from 25 to 90 C. Applied Geochemistry, (1): p [10] Khormali, A., D.G. Petrakov, and G. Yuryevich Shcherbakov, An In-depth Study of Calcium Carbonate Scale Formation and Inhibition. Iranian Journal of Oil & Gas Science and Technology, (4): p [11] Boak, L.S., Factors that impact scale inhibitor mechanisms, 2013, Heriot-Watt University. [12] Merdhah, A.B. and A.A.M. Yassin, Study of scale formation in oil reservoir during water injection-a review [13] Kiaei, Z. and A. Haghtalab, Experimental study of using Ca-DTPMP nanoparticles in inhibition of CaCO 3 scaling in a bulk water process. Desalination, : p [14] Merdhah, A.B. and A.A.M. Yassin, Solubility of common oil field scales of injection water and high-barium concentration and high-salinity formation water. Jurnal Teknologi, : p [15] Haghtalab, A. and Z. Kiaei, Evaluation of the effective parameters in synthesis of the nano-structured scaling inhibitors applicable in oil fields with sea water injection process. Journal of Nanoparticle Research, (10): p [16] Hasson, D., et al., Influence of the flow system on the inhibitory action of CaCO 3 scale prevention additives. Desalination, (1): p [17] Amjad, Z., Calcium sulfate dihydrate (gypsum) scale formation on heat exchanger surfaces: The influence of scale inhibitors. Journal of colloid and interface science, (2): p [18] Amjad, Z. and J. Hooley, Influence of polyelectrolytes on the crystal growth of calcium sulfate dihydrate. Journal of colloid and interface science, (2): p [19] Zhou, B., Technology of Industrial Water Treatment, 2002, Chemical Industry Press, Beijing, PR China. [20] Amjad, Z., Performance of polymers as precipitation inhibitors for calcium phosphonate. Tenside, surfactants, detergents, (2): p [21] Chen, C.Y., M.Z. Xia, and F.Y. Wang. Influence of three organic phosphonates on calcite crystal growth. in Advanced Materials Research Trans Tech Publ. [22] Xia, M. and C. Chen, Probing the Inhibitory Mechanism of Calcite Precipitation by Organic Phosphonates in Industrial Water Cooling System. International Journal of Environmental Science and Development, (4): p [23] Zhang, P., et al., Surfactant-assisted synthesis of metal-phosphonate inhibitor nanoparticles and transport in porous media. SPE Journal, (03): p [24] Nowack, B., Environmental chemistry of phosphonates. Water Research, (11): p

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