Estudos dos fenômenos de adsorção e precipitação de inibidores de incrustação em rocha arenítica por meio de ensaios estáticos e dinâmicos

Abstract

Scale inhibitors used in the squeeze treatments allows the use of the seawater injection in wells with low oil and gas production, because reduce the damage caused by insoluble salts deposition. The squeeze treatment yield depends on the duration of the inhibitor in the production well, which depends on the rock-interaction type, which may be adsorption or precipitation. Thus, this theses aim is indicator of the interaction between scale inhibitor and sandstone, in order to identify the different adsorption and precipitation phenomena, through three experimental methods: one static and two dynamic. In the static experiment, the trimethylphosphonic acid (ATMP) inhibitor interaction was evaluated varying the chemical composition of the rock, at 25 and 70 ºC, at pH 4 and 7. The sandstone constituents quartz, feldspar, kaolin and biotite mica were tested. In addition, it was evaluated the influence of the calcium ions (Ca2+) in the brine on the ATMP retention. The minerals were characterized by X-ray fluorescence (XFR) and nitrogen sorption at -196 ° C for chemical composition quantification and surface area determination (SBET), respectively. The ATMP concentration was measured using the coupled plasma optic spectrometry (ICP-OES) technique. In the static experiment, it was confirmed that biotite mica had a higher retention of ATMP, due to the heterogeneity of its chemical composition. The adsorption on the surface had been predominant, for all minerals studied at 25 ° C, and at 70 ° C, the minerals feldspar, kaolin and biotite mica were leached, which led to a precipitation of the anti-fouling as cation-ATMP complex. This significantly increased the ATMP retention, especially in the tests with biotitic mica. Precipitation was detected in the tests with Ca2+ in the brine. This was more evident at pH 7 and at 70 ºC, and was also observed in the dynamic tests, performed at pH 4. In the dynamic tests in fixed bed, the ATMP and diethylenetriamine pentamethylphosphonic acid (DETPMP) retentions were studied. The beds were packed with quartz and berea, operated at 70 ºC, under flow rate of 0.1 mL/min and pH 4. Retentions around 16 % were obtained in the systems with Ca2+, which ensured ATMP and DETPMP retention by precipitation and adsorption, since the inhibitors recovery with 100 VP in the postflush was 50 % for a berea and 90 % quartz. The use of integral mass balances allowed a determination of the retained amount of ATMP and DETPMP in the bed. The desorption curves profile in postflush allowed the identification of the precipitation phenomenon, due to the deposition of Ca-inhibitor complex, during shut-in. Lastly, in the dynamic tests with coreflood, the average retention was 30 %, while the recovery was lower than 6 %, in berea sandstone cores with a mean porosity of 17 %. The occurrence of precipitation in coreflood tests was limited to the inhibitor injection step. The fragmentation of the core to perform the tests in column did not expose the minerals present in the berea, validating the application of the fixed bed method to evaluate the scale inhibitor retained in sandstone rocks. In conclusion, Ca2+ ions are responsible for increasing the retention of phosphate inhibitors, both by adsorption and precipitation. In heterogeneous rock, the possibility of precipitation is higher and in rocks with more aluminosilicate compounds, the Ca2+ ions insures the inhibitory molecules retention by adsorption.