No abstract

Kinetic hydrate inhibitors (KHIs) have been serving the petroleum industry for many years. They are normally used at dose rates of <3% of the produced water, resulting in considerable savings in CAPEX/OPEX. However, several uncertainties and challenges have prevented their more widespread usage, including a lack of consistent test protocols, poor repeatability of test results, concerns over performance under shut-in conditions, the potential risk of hydrate formation at the top of the pipelines, and relatively low cloud points/fouling issues, which can cause problems in produced water handling/ reinjection (PWRI) and/or monoethylene glycol (MEG) regeneration schemes. In this communication, we present the latest developments related to KHIs, including the results of a testing technique based on crystal growth inhibition that produces reliable and repeatable results, KHI performance under shut-in conditions, risk of hydrates at the top of pipelines, and a technique for removing KHIs from produced water prior to PWRI or MEG regeneration. We also demonstrate that it is possible to predict the potential suitability of KHI-based solutions for any specific field application prior to even starting the experimental campaign and/or designing a KHI + THI combination (where THI denotes thermodynamic hydrate inhibitor). Results show that MEG is an excellent synergist for the KHIs investigated, and 1% KHI can replace large quantities of MEG. Considering the fact that many of the operational challenges and uncertainties associated with KHIs have recently been addressed and that there are excellent opportunities for combining KHIs with MEG, we expect resurgence in KHIs as a reliable and economical option for preventing gas hydrate problems. This could have significant economic and environmental impact, as well as extend the life of petroleum reservoirs.

Low dosage hydrate inhibitors (LDHIs)antiagglomerants (AAs) and kinetic hydrate inhibitors (KHIs)are increasingly used as an alternative to the traditional thermodynamic hydrate inhibitors for controlling gas hydrate problems in the petroleum industry. As nucleation inhibitors, KHIs induce an extended induction time (t i ) at particular subcoolings before nucleation of hydrate can proceed to growth. However, due to the stochastic nature of nucleation, gaining repeatable and transferrable induction time results can be very challenging and time-consuming. To overcome this problem, study on KHI crystal growth inhibition (CGI) has yielded a KHI evaluation technique which is considerably simpler than induction time measurements. Moreover, this study shows that KHIs create a number of well-defined hydrate CGI regions as a function of subcooling which are completely repeatable and transferrable between different setups. These regions range from complete inhibition (CIR), to slow growth region (SGR), and ultimately to rapid growth region (RGR) as subcooling increases, making KHI assessment more rapid and reliable. Furthermore, results revealed that a true induction time can only be measured for a relatively short-range of subcooling within the SGR and RGR. Likewise, hydrate nucleation induction time is impossible to measure in the CIR, supporting CGI studies which show that hydrate growth is completely/indefinitely inhibited in this subcooling range.

No abstract

Kinetic hydrate inhibitors (KHIs) offer an alternative to traditional thermodynamic hydrate inhibitors (THIs) for the prevention of gas hydrates. KHIs have several advantages over THIs, such as lower required volumes, easier logistics and reduced CAPEX. However, KHIs are once through chemicals leading to increased OPEX, are mostly non-biodegradable and therefore cannot be discharged to sea or disposal wells in fear of aquifer pollution. KHIs can also lead to fouling of process equipment, especially at elevated temperatures. To resolve these issues, a new KHI polymer removal method using a solvent extraction-based technique has been developed. In this approach, an immiscible extraction fluid is mixed into the KHI containing aqueous phase where the KHI polymer partitions into the extraction fluid, which can then be separated from the aqueous phase. In some cases, the KHI separated this way can be re-used. This process has the potential to solve problems with KHI produced water treatment/disposal, including where KHI is used in combination with MEG, reducing the costs and process fouling and protecting the environment. A new joint industry project (JIP) is underway with the aim of developing the concept into a commercial process for removal and possible re-use of KHIs upstream of PW treatment or MEG Regeneration systems. The first phase of this project is lab scale evaluation of the solvent extraction method for simulated removal and re-use of two commercial KHI formulations for a real gas-condensate field case. Both the removal efficiency and hydrate inhibition performance of 4 cycles of re-injected/re-used KHI has been successfully demonstrated. Removal of KHI from a real MEG system case was also successfully demonstrated. In the second phase of the JIP, lab scale tests were used to screen extraction and separation equipment and identify optimum process conditions. The upcoming third phase of this JIP is dedicated to demonstrating the selected process concept(s) on pilot scale in a flow loop. In this proceeding we will give highlights of the early laboratory test results from a produced water case where two field qualified KHIs are removed from PW and reused 4 times, still showing adequate hydrate inhibition performance. Successful pilot tests will confirm the operability of this process in the field.