Factors Affecting the Stability of Scale Inhibitors Used for Capillary Injection in High Temperature Wells

Abstract

Abstract In recent years, the percentage of oil production from more challenging environments has increased. In addition to the numerous engineering and logistical difficulties of working at increased depth, temperature and pressure these production zones provide a harsh environment deleterious to the performance of some critical oilfield chemicals. Scale inhibitors are one class of oil field chemicals which are deployed through squeeze treatments into the formation and/or continuous downhole injection for protection of production tubulars. As well depths continue to increase, the exposure time of the injected chemicals also increases. With temperatures in the range of 180-200 °C and pressures exceeding 10,000 psi, the effect of elevated temperature and pressure on scale inhibitor performance is a critical parameter to evaluate using chemical analytical techniques and product performance methods. Another trend leading to increased thermal exposure is the use of thermal enhanced recovery techniques. Scale inhibitors are exposed to high temperatures in operations such as steam flooding and steam assisted gravity drainage (SAGD). In this study, a range of chemicals have been evaluated for their short and medium-term thermal stability at 180 and 200 °C. The primary application of this data is for downhole injection and squeeze treatments prior to adsorption. Inhibitor chemical types include sulfonated polycarboxylic acid (SPCA), fluorescent tagged sulfonated polycarboxylic acid (FSPCA), phosphorous tagged sulfonated polycarboxylic acid (PSPCA), sulfonated polyacrylocarboxylic acid (SPAC), polyacrylic acid (PAA), polyvinyl sulfonate (PVS), polyamino polyether methylene phosphonate (PAPEMP), bis(hexamethylene)triamine pentakis(methylene phosphonic acid) (BHTPMP) and diethylenetriamine pentakis(methylene phosphonic acid) (DTPMP). In most cases the sodium or potassium salts of the inhibitors are used. The chemical effect of temperature on scale inhibitors is measured through molecular weight determination, thermogravimetric analysis (TGA), pH change, and Fourier Transform Infrared (FTIR) analysis. The performance of these inhibitors is measured under static and dynamic conditions for inhibition of barium sulfate scale. These results help to further the knowledge of inhibitor degradation due to thermal effects and indicate the direction for further product development of thermally stable scale inhibitors.