Most non-polymeric oilfield scale inhibitors contain aminomethylenephosphonate groups. They generally have poor biodegradability, limiting their use in regions with strict environmental regions, such as offshore Norway. From mono-and bisnitrile starting materials, we have synthesized and investigated compounds with one or two aminobisphosphonate groups, −C(NH 2 )(PO 3 H 2 ) 2 , for seawater biodegradability, their calcium carbonate and barium sulfate scale inhibition, and compatibility with Ca 2+ ions. The distance between these groups was shown to affect biodegradability, with aminobisphosphonate derived from adiponitrile, (1,6-diaminohexane-1,1,6,6-tetrayl)tetraphosphonic acid (BP-7), giving the highest biodegradation of 25% in 28 days by the OECD 306 seawater test. All of the synthesized inhibitors exhibited both carbonate and sulfate scale inhibition properties. In comparison to known commercial scale inhibitors, the scale inhibition performance was relatively poor for sulfate scale and moderate for carbonate scale. To improve the performance, the amine groups were converted to aminobismethylenephosphonate groups, −N(CH 2 PO 3 H 2 ) 2 , to give novel non-polymeric scale inhibitors with 4−8 phosphonate groups. The scale inhibition was much improved for carbonate and sulfate scales. One of these compounds, BP-9, was found to be the most potent scale inhibitor, with a fail inhibitor concentration at 5 ppm for carbonate scale and 20 ppm for sulfate scale. The new bisphosphonate compounds showed moderate biodegradation activity. For example, compound BP-8 gave 40% seawater biodegradation over 28 days in the OECD 306 test.

Scaling is one of the most frequently stated problems in the oil industry, and scale inhibitors (SIs) are applied to prevent its formation. Organophosphonates are well-known types of SIs, particularly useful for squeeze treatments, which can be found as both non-polymeric and polymeric molecules. However, the performance of phosphonate-based SIs is often limited by poor compatibility with calcium ions. In addition, many phosphonated SIs exhibit poor seawater biodegradation. Therefore, there is still a need to develop effective SIs with reliable calcium compatibility, thermal stability, and environmental acceptability. A series of linear and branched phosphonated polyetheramines were synthesized. The final products were evaluated for their calcium carbonate (calcite) and barium sulfate (barite) scale inhibition performance using a high-pressure dynamic tube blocking rig at 80 bar and 100 °C. This study showed that the best phosphonated polyetheramines had excellent performance on both barite and calcite scale formation compared to some common commercial phosphonated SIs. In addition, all of the synthesized SIs showed superior compatibility with calcium ions and good thermal stability at 130 °C. The linear phosphonated polyetheramines gave the best seawater biodegradability, with BOD28 up to 47% by the OECD 306 procedure.

Hydrophobically modified methacryl- and acrylamide polymers are well-known kinetic hydrate inhibitors (KHIs). Polymers of N-isopropylmethacrylamide (IPMAM) are now commercially available. However, both polyIPMAM and N-isopropylacrylamide homopolymer (polyIPAM) have low cloud and deposition points, making it difficult to use them in the field because of precipitation problems. Comonomers that are more hydrophilic can be copolymerized with IPMAM or IPAM to raise the cloud point. In this work, we have synthesized and investigated a series of new copolymers of IPAM and a new dimethylhydrazidoacrylamide monomer (DMHAM) as KHIs for the first time using high-pressure gas hydrate rocker rig equipment. The novel polymers have high cloud points in deionized water and also in brine solutions compared to polyIPAM. A 1:2 copolymer of DMHAM/IPAM gave the highest KHI performance for this class of copolymer with a cloud point at 58 °C in deionized water. A 1:1 copolymer gave only a small reduction in performance but has a cloud point of 83 °C in 3.6% NaCl and no cloud point in deionized water. Tests were carried out using high-pressure slow constant cooling rocking cell experiments with a structure-II-forming natural gas mixture at approximately 80 bar.

Poly(N,N-dimethylhydrazidoacrylamides)s (PDMHAMs) and a series of copolymers of (N,N-dimethylhydrazidoacrylamide) and (N-isopropylacrylamide) were recently investigated as kinetic hydrate inhibitors (KHIs). Poly(Nvinylcaprolactam) (PVCap) and related copolymers have been used as a class of commercial KHIs in the oil and gas industry to prevent plugging of pipelines with gas hydrates. In this study, we have synthesized and investigated the ability of copolymers of DMHAM monomer and VCap monomer to inhibit structure II gas hydrate formation in high-pressure rocking cells at approximately 75 bar. Various polymer molecular weights have been investigated at various pH conditions. It was found that the novel polymers have high cloud points in deionized (DI) water or brine solutions at high or low pH under pressure compared to polyVCap. A 1:2 copolymer of DMHAM/VCap gave the best KHI performance for this class of copolymer with a cloud point at 50°C in DI water. Also, a 1:1 DMHAM/VCap copolymer gave excellent KHI performance, as well as giving no cloud point up to 100°C in DI water or high-salinity solutions (3.6−15 wt % NaCl) at pH 5.0. The cloud point was found to be 67°C at pH 12.0 for the 15 wt % NaCl solution, making it compatible for use in high-salinity water-based deep-water drilling fluids. It was also found that high pH improved the performance of the KHIs compared to otherwise identical tests at pH 5.0. This may be related to removing the structure I (SI)-forming and relatively more soluble acid gas CO 2 from the system at high pH.