Fundamental Understanding on the Effects of Anti-Agglomerants Towards Overboard Water Quality
Authors: Webber Peter Andrew 
Published: July 2010

Offshore production facilities that incorporate anti-agglomerate (AA) technology for their hydrate inhibition strategy must ensure chemical performance as well as chemical compatibility with the facility processes, i.e. emulsion tendencies, water quality, etc. Bottle testing has been the traditional method for evaluating water quality, emulsion tendencies, and oil/water separation for a system. It is not uncommon for a series of bottle tests to require a significant volume of fluids and evaluation of several AA candidates, yet it is often the case that only small volumes of produced fluids are available to complete this testing.

This paper describes the coupling of several techniques to develop a predictive tool for water quality assessment in the traditional emulsion tendency bottle test. These techniques are then compared with bottle test results for validation with the overall goal to reduce the volume demand for field fluids. The bottle test is the predominant experiment to predict separation patterns of produced fluids and water quality issues and is used as the benchmark for comparison purposes in this study. This hybrid approach has been successful for rapid throughput of service work, screening of new chemistries, and enhanced understanding of fundamental AA structure-activity relationships.

As anti-agglomerate chemistries are traditionally interface-active, challenges typically arise in the areas of emulsion formation and phase partitioning. Three distinct techniques to compliment the standard bottle test will be detailed as well as the results. Parameters including interfacial rheology, emulsion characterization, phase partitioning, and free water quality were found to be important factors in the selection of the appropriate AA-LDHI. To date, emulsion tendency has not been analyzed by these methods for a number of production systems that utilize AA-LDHI surfactants.

Introduction

Anti-agglomerate technologies are commonly utilized for chemical inhibition of natural gas hydrates. AAs are typically surfactants, possessing a hydrophilic head and a hydrophobic tail. The most common class of AAs are quaternary ammonium compounds. Their mechanism of inhibition is postulated to involve incorporation of the polar head in the growing hydrate crystal. This interaction disrupts the growth process resulting in smaller hydrate crystals. Furthermore, the hydrophobic tail functions to disperse the hydrate into the hydrocarbon phase preventing further agglomeration into plugs. Finally, the hydrate crystals are transported as slurry through the production stream (Kelland, M.A. et al, York, J.D. et al)

Anti-agglomerates permit the growth of hydrates but remediate by dispersion and are often preferred for well production shut-ins and cold start-ups for this reason. They also find application since their performance is relatively unaffected by the degree of subcooling, their ability to tolerate high brine systems, and their compatibility with most production chemicals.

Implementations of anti-agglomerate treatment programs often come with unintended challenges. The tendency for surfactants to enhance and stabilize emulsion as well as ineffectively separate aqueous and hydrocarbon fluids topsides are of the utmost nuisance to oilfield production (Ghannam, M.T., Adamson, A. W. et al). If additional emulsion processing and water clarification programs are required to treat the issues created by anti-agglomerates, producers are inclined to rely on alternative hydrate inhibition methods.