Sulfonated Nonpolymeric Aminophosphonate Scale Inhibitors-Improving the Compatibility and Biodegradability

Phosphonate-based scale inhibitors are widely used in the upstream oil and gas industry, but many of them lack good compatibility with high calcium brines. Here, we report the synthesis of several nonpolymeric amino-bismethylenephosphonates with an added sulfonate group to improve the compatibility. The chemicals are 2-(bis(phosphonomethyl)amino)alkane-1-sulfonic acid (alkane = methane, ethane, and propane labeled SI-1 to SI-3, respectively), N,N-bis(phosphonomethyl)cysteic acid (SI-4), and N,N-bis(phosphonomethyl) metanilic acid (SI-5). To screen their performance, we carried out dynamic scale loop inhibition performance tests for calcium carbonate and barium sulfate, thermal stability tests, and calcium compatibility tests up to 10 000 ppm calcium ions and compared them to some well-known oilfield scale inhibitors. Seawater biodegradation over 28 days (BOD28) was also investigated by the OECD 306 method. All new inhibitors demonstrated good calcite inhibition properties, but only SI-1 and SI-2 gave fairly good barite inhibition. SI-2 stood out as an excellent calcite inhibitor, suitable for use in very high calcium-containing brines. SI-2 could also provide protection against barite deposition under mild to medium scaling potentials and gave a reasonable rate of biodegradation (BOD28 = 46%). SI-1 and SI-4 gave BOD28 values of 79 and 84%, respectively, and can be classed as readily biodegradable. Of the two products, SI-1 seems the most promising for further studies given the better calcite and barite scale inhibition properties. Of the SIs tested, SI-5 showed the best thermal stability at 130 degrees C and could therefore be a useful downhole squeeze SI for fairly high-temperature wells. Its BOD28 value was 41%. Overall, the study highlights the difficulty of designing a scale inhibitor with all of the major features required for application over a wide range of field conditions.