Systematic Molecular-Size Variants in Diphosphonate Inhibitors for Oilfield Scale Management

Abstract

Organophosphorus-based scale inhibitors (SIs) have been widely used in the petroleum industry for several decades. Among them, aminomethylenephosphonates (possessing at least one −NH+–CH2–PO3H– moiety) have shown outstanding inhibition efficiency against carbonate and sulfate oilfield scales. However, one of the main drawbacks of aminomethylenephosphonate-based SIs with multiple phosphonate (−PO3H2) groups is their poor tolerance against high-calcium brines. In this work, the calcium tolerance of aminomethylenephosphonates was improved by reducing the number phosphonate groups in the inhibitor backbone to less than three and introducing a variable-length non-polar alkyl side chain while maintaining acceptable inhibitory efficiency levels. Hence, we synthesized a series of variable-length alkyl chain-based amino-di(methylenphosphonate) [(H2O3P–CH2)2–N–(X)] inhibitors, (X = methyl, ethyl, propyl, butyl, hexyl, octyl, and dodecyl). In addition, we also studied the role of the alkyl side-chain length in the diphosphonate structure backbone on the scale inhibitory activity. All newly synthesized aminomethylenediphosphonates were evaluated as SIs for calcium carbonate (calcite) and barium sulfate (barite) in brines based on the Heidrun oilfield using a high-pressure dynamic tube blocking rig at 100 °C and 80 bar. Furthermore, we investigated the calcium compatibility of all aminomethylenediphosphonate SIs at several levels of calcium stresses. The new aminoalkyldiphosphonate inhibitors possessing shorter alkyl chain lengths (X = methyl, ethyl, propyl, butyl, and hexyl) gave better calcite scale inhibition performance and outstanding calcium compatibility of up to 1000 ppm of Ca2+ compared to the commercial benchmark ATMP SI [amino-tris(methylenephosphonate)] and longer alkyl-chain diphosphonates, that is, octylamine-N,N-di(methylenephosphonate) (ODMP, C8-D) and dodecylamine-N,N-di(methylenephosphonate) (DDMP, C12-D). Moreover, we tested the thermal stability (at 130 °C for one week) of the best-performing additive (based on calcite inhibition and calcium tolerance performances), and it was found that methylamine-N,N-dimethylenephosphonate (MDMP, C1-D) was thermally stable under these harsh conditions without any loss of its inhibition performance. The Ca-C8-D “complex” was deliberately synthesized and structurally characterized. It appears that the major factor for its poor Ca tolerance is the tight packing of the octyl side-chain groups.

Flexible, Linear, and Systematically Expanded Tetraphosphonate Bolaamphiphiles and Their Inhibition Performance against Calcite and Barite Scale Formation

“…In the last 10 years, our research group has developed several potent phosphonate-based SIs for mitigating various oilfield inorganic scales − and metallic corrosion. , We recently investigated the inhibitory activity of SIs based on alkylmonoamine–di­(methylenephosphonic acid) backbones, with the alkyl chain being a variable-length aliphatic moiety …”

“…23,24 We recently investigated the inhibitory activity of SIs based on alkylmonoamine−di(methylenephosphonic acid) backbones, with the alkyl chain being a variable-length aliphatic moiety. 25 Although there are no reports on the systematic influence of the structural architecture of the alkyldiamine−tetrakis-(methylenephosphonate) SIs on the inhibition of calcite or barite scaling under oilfield production conditions, some notable but scattered examples exist. These cases include prevention of CaCO 3 scaling in reverse osmosis (RO) applications, 26 inhibition of gypsum, 27 and barite in the presence of Na + or Zn 2+ .…”

Enhancement of Polyacrylate Antiscalant Activity during Gypsum Deposit Formation with the Pretreatment of Aqueous Solutions with Spruce Wood Shavings

“…[3]. Among these, the most effective and widely used approach is the application of chemicals that inhibit scale formation at sub-stoichiometric levels [1,[4][5][6].…”

“…Similarly, there is a wide variety of views on the activity of antiscalants [1,[4][5][6][7][25][26][27][28][29][30][31][32]. The scale inhibitors may act in a bulk aqueous medium through several possible routes.…”