Investigation of calcium carbonate scale inhibitioand scale morphology by scanning electron microscopy

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Calcium carbonate scale inhibition in squeeze treatment by the phosphonate–type scale inhibitors, such as diethylenetriamine penta (methylene phosphonic acid) (DETPMP), ethylene diamine tetra(methyelne phosphonic acid) (EDTMP) or by the mixing of DETPMP, EDTMP and chelants (citric acid (CA), maleic acid (MA), ethylendiamintetraacetic acid (EDTA) has been studied in previous works [5,6]. This paper focused on several aspects concerning calcium carbonate scale inhibition mechanism of DETPMP and of the mixing of DETPMP with trace of chelants by scale morphology on scanning electron microscopy (SEM). From the SEM photos, it can be observed that the presence of the inhibitors, especially with the right ones, causes

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Nội dung Text: Investigation of calcium carbonate scale inhibitioand scale morphology by scanning electron microscopy

Journal of Chemistry, Vol. 43 (3), P. 384 - 387, 2005 INVESTIGATION OF CALCIUM CARBONATE SCALE INHIBITION AND SCALE MORPHOLOGY BY SCANNING ELECTRON MICROSCOPY Received 23rd-June-2004 Nguyen Thi Phuong Phong Institute of Materials Science Hochiminh City branch, Hochiminh City SUMMARY Calcium carbonate scale inhibition in squeeze treatment by the phosphonate–type scale inhibitors, such as diethylenetriamine penta (methylene phosphonic acid) (DETPMP), ethylene diamine tetra(methyelne phosphonic acid) (EDTMP) or by the mixing of DETPMP, EDTMP and chelants (citric acid (CA), maleic acid (MA), ethylendiamintetraacetic acid (EDTA) has been studied in previous works [5, 6]. This paper focused on several aspects concerning calcium carbonate scale inhibition mechanism of DETPMP and of the mixing of DETPMP with trace of chelants by scale morphology on scanning electron microscopy (SEM). From the SEM photos, it can be observed that the presence of the inhibitors, especially with the right ones, causes deformation of the crystal morphology of both the adhered and precipitated crystals. The strong depression of adhesion of crystal (calcite) is caused by the adsorption of inhibitor on its surface. I - INTRODUCTION most cost-effective inhibitors of sulfate scale at reservoir conditions, but they are limited for Oilfield scale is practically a ubiquitous inhibition of CaCO3 scale. The improving problem in oilfield operations. It can form when CaCO3 scale inhibition has obtained by mixing incompatible waters mix, for example during of phosphonate DETPMP and a trace of water flood, or it can form when reservoir chelating agent such as CA, MA, EDTA [7]. In pressure and temperature changes are endured this paper, the CaCO3 scale morphology has by self-scaling brines. Sulfat scale commonly been observed by scanning electron microscopy occurs with the former mechanism and carbonat (SEM) in order to find significant differences in scale with the latter [1, 2]. the morphologies between the presence and the CaCO3 scale deposition depends upon the absence of inhibitors and to understand better temperature of the fluid: calcium carbonate the CaCO3 scale inhibition mechanisms. scale exists predominantly in calcite form at temperature of < 50oC, and exists predominantly II - EXPERIMENTAL in aragonite form at temperature of > 65oC. Laboratory studies were performed to Carbonate calcium has in practice three poly- evaluate of inhibition efficiency of DETPMP in morphs forms: calcite (hexagonal), aragonite the absence and the presence of trace of chelant (ortho-rhombic), and vaterite (hexagonal) CA. depending on the increasing solubility and decreasing thermo-dynamic stability. Chemicals In our works [5, 6] phosphonates are the - DETPMP (concentration 30%; pH = 6.5) is 384 synthesized by Lab of Magnetochemistry, of bottles were filtered through filter paper 0.2 µm Institute of Materials Science Hochiminh City and were dried at 50oC. Investigation of crystal Branch. morphology was performed on the SEM, JOEL - Citric acid 98%, Russia, is used as solution JSM-5300, Japan. of 1%. III - RESULTS AND DISCUSSION - EDTA pure, Merck, is used as solution of 1%. 1. Crystal morphology and polymorphous of - Murexide, Merck (purpurat ammonium), is CaCO3 used as solution of 1%. In the uninhibited system, most of the - Synthesis brines. precipitates in the solution are orthorhombic Procedures calcite particles with average particle size of 10 µm were formed on the bottom of test bottles Inhibition efficiency was determined by (Fig. 1). During aging process (aging testing method NACE Standard TM 03-074-95 temperature of 70oC; aging time of 48 hours), [4]. Inhibition efficiency is calculated according the population of calcite crystals adhered on the to the following equation: solid surface. On the other hand, the particle [Ca ] [Ca ] 2+ in 2+ non in × 100 sizes of vaterite and aragonite crystals in the % ICa = [Ca ] [Ca ] 2+ i 2+ non in solution are about 100 µm (Fig. 2). These facts indicate that the calcite on the surface nucleates % ICa: percent calcium inhibition and grows by direct crystallization of the lattice [Ca2+]in: soluble calcium concentration of the ion in solution. The aragonite, vaterite crystals inhibited sample. precipitate at high temperature with large sizes. [Ca2+]non-in: soluble calcium concentration of They are in the upper layer, and easily flow with the uninhibited sample fluids. Calcite precipitates at low temperature [Ca2+]i: initial soluble calcium concentration with smaller crystals. However, at high temperature and long aging time, these calcite Soluble calcium concentration is titrated crystals have strong adhesion and stick on the with standard EDTA solution and murexide bottom of the bottle and it is difficult to treat (ammonium purpurate) indicator. away. It can be seen that in the absence of the After NACE tests, all solutions in test inhibitor, calcite is the main crystal form. Fig. 1: SEM picture of the calcite crystals adhere Fig. 2: SEM picture of the aragonit/vaterite on the surface in the uninhibited system crystals in the uninhibited system The SEM pictures of particles adhered on the presence of the inhibitor are shown in Figs the surface and precipitated in the solution in from 3 to 6. The crystal morphology of adhered 385 calcite during aging time changes to form main polymorphs in the presence of the polycrystalline calcite by the presence of inhibitor. The aragonite/vaterite crystals have inhibitor. This morphology change may be two beneficial effects in comparison with calcite caused by a partial covering of the crystal crystals: (1) the aragonite/vaterite crystals will surface by the inhibitor. In the presence of the not adhere together to form a scale in the same inhibitor, amount of the adhered calcite is way as calcite crystals would do; (2) the markedly decreased and the particle size is presence of aragonite/vaterite crystals will upset relatively large compared with that in the the equilibrium between the fluid and any absence of the inhibitor (Figs. 3&4). In the case existing scale. In the presence of DETPMP, the of the most suitable inhibitor, DETPMP: CA (2 : CaCO3 scale inhibition efficiency is low (< 1) (the inhibition efficiency is upper 80%), the 35%, 10 ppm, 70oC, 48 h), but their treatment is calcite crystals have loose structure with the rather easily because the aragonite crystals are holes and they are less adhesive (Fig. 4). predominant (Fig. 5). With the DETPMP: CA, the scale inhibition efficiency is the best, the The aragonite/vaterite crystals become the vaterite polymorphs is prominent (Fig. 6). Fig 3: SEM picture of the calcite crystals in Fig. 4: SEM picture of the calcite crystals in the the presence of 10 ppm DETPMP after 48 h presence of 10 ppm DETPMP : CA (2 : 1) after 48 h Fig. 5: SEM picture of the aragonite/vaterite Fig. 6: SEM picture of the aragonite/veterite crystals in the presence of 10 ppm DETPMP crystals in the presence of 10 ppm DETPMP : CA after 48 h (2 : 1) after 48 h 2. Inhibition mechanism thus preventing further crystal growth by It is generally believed that the inhibitor interference with the growth process. The molecules must adsorb at the active growth sites inhibition of scale formation is affected by both on the surface, which may be crystal defects, the location of the adsorbed inhibitor at the 386 crystal surface and the extent of chemical influences not only the growth rate but also the bonding with the surface. Related study [3] morphology and the nature of the scale. shows that less than 5% of the crystal surface is *In the absence of the inhibitor, calcite is covered by adsorbat molecules. This suggests the main crystal form. that the inhibitor molecules are preferentially adsorbed at the most active growth sites (kinks) *In the presence of inhibitors, the crystal on the surface, alter the surface properties of the habit has been modified, aragonite and vaterite crystals, and may affect nucleation rate, crystal become the main polymorphs. growth. 3. In the presence of the most suitable DETPMP, CA adsorbed on CaCO3 surfaces inhibitor, vaterite is the main crystal form. by binding the carboxylic or phosphonat anions to surface of calcium ions. It was found that the REFERENCES inhibition effect of inhibitor is related to their surface-binding capability. Thus, we show that, 2. R. J. Powell, R. D. Gdanski, M. A. McCabe, the DETPMP: CA mixture contains carbonyl D. C. Buster. Controlled release scale and phosphonic groups; therefore, its surface inhibitor for use in fracturing treatments, binding capability is stronger than that of SPE 28999 (1995). DETPMP. Thus, DETPMP: CA possesses higher 3. Malandrino, Eniricerche SPA, M. D. Yuan, inhibition efficiency than DETPMP under the K. S. Sorbie, M. M. Jordan. Mechanistic same conditions (CaCO3 inhibition efficiency of study and modelling of precipitation scale DETPMP is 30.12%; of DETPMP : CA (4 : 1) is inhibitor squeeze processes, SPE 29001 63.3%; of DETPMP : CA (3 : 1) is 65.14%; (1995). DETPMP : CA (2 : 1) is 80.8%; DETPMP : CA 3. Voloshin, V. V. Ragulin. Scaling problems (1 : 1) is 52.2%. We also show that the synergic in Western Siberia, SPE 80407 (2003). effect of the chelating agent CA has shown as the primary chelant and DETPMP, as the 4. NACE Standard TM 03-74. Laboratory test secondary one. The first agent chelates the to determine the ability of scale inhibitors to calcium ion before it is mixed with the prevent the precipitation of calcium sulfate phosphonate scale inhibitor. This phosphonate is and Calcium Carbonate from solution, the second, and stronger, chelating agent. That national association of corrosion Engineers, fraction of the calcium ion is unchelated by Houston, Texas (1995). weaker, primary chelant will be chelated by the 5. N. P. Tung, N. T. P. Phong, et al. The secondary chelant, i.e., the phosphonate. This synthesis of organic phosphonate phosphonate plays a role as a strong chelating Compounds for scale inhibition in squeeze agent. 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