| Abstract |
Four cases of blockages and deposition of injection tubings used for calcite inhibition systems are presented. Blockages inside injection tubings were caused by: 1) dehydration and crystallization upon flashing of inhibitor, 2) thermal degradation of inhibitor resulting in insoluble products, 3) corrosion products from surface facilities, 4) incomplete filtration of impurities in water used for dilution of chemical. FT-IR spectra shows the thermal degradation of the polyacrylate at Tí▌240íπC. Likely product is a polyanhydride, which is expected to have a rigid backbone and lesser solubility in water. The polyacrylates also precipitate through cross linking forming a gel network in the of S or S containing compounds at high temperatures. The black tar like material formed is insoluble even to the most aggressive cleaning agent. At higher temperatures (>280íπC)), thermal degradation results in complete breakdown of the polymer back bone and lost of inhibition. There is also evidence of high temperature corrosion inside the capillary tubing in the presence of S. Petrographic and thermodynamic calculations have shown the presence of stable NiS products at 280íπC. Use of polyacrylate based anti-scalant chemical formulations should be limited to geothermal wells where injection temperature is <250íπC. Recommendations to avoid similar blockages in injection tubings used for calcite inhibition systems are forwarded. |