Antibody Based Technique for Offshore Scale Inhibitor Detection
Authors: Williams G.D. , Mcrae J.A. , Heath S.M. , Strachan G. , Porter A. , Macguire I. , Charlton K.A. 
Published: December 2007

The accurate and timely analysis of oilfield chemicals is crucial in allowing cost effective chemical management. Unfortunately, many of the current detection methods are time consuming and are not appropriate for on-site applications. Clariant Oil Services and Haptogen Ltd have developed a detection kit that allows accurate on-site, same day chemical analysis. The test kit has been designed in a simple format, allowing analysis to be performed offshore and without the need for laboratory facilities. The test method is based on antibodies that specifically bind to a single production chemical molecule, allowing detection of the molecule without interference from other species which may be present in produced water samples. Antibodies have been developed for a specific, polymer based scale inhibitor used on a North Sea field that exhibits a harsh scaling environment. These antibodies have been evaluated in the laboratory in comparison with traditional test methods and found to be accurate at concentrations down to below 1ppm of applied scale inhibitor. It is now planned to evaluate the kit in the field. Future work will also build up a suite of antibodies, which will allow detection of a wide range of production chemicals using this technique.

Introduction

A wide range of chemicals may be used during production operations, such as scale, corrosion, wax and hydrate inhibitors, containing many different molecular species. Often it is important to have the ability to measure unknown concentrations of chemical returning from the production system. For example, in the North Sea, scale inhibitors are often "squeezed" into a well, and protect the well from scaling as the inhibitor is retired in the produced water. Over time, the concentration of scale inhibitor in the produced water declines as the treatment becomes exhausted, until the level is too low to provide effective protection and it becomes necessary to re-treat the well. The point at which this will occur cannot always be accurately predicted, and so it is usually necessary to analyse produced water samples for scale inhibitor content on a regular basis, in order to know when to re-squeeze. In some harsh scaling conditions, more than 100kg can deposit per 1000bbl of produced water1. It is therefore potentially of great economic benefit to have a rapid and reliable analysis method on which to base decisions to re-treat, and so ensure well integrity. Furthermore, the cost of treating a well can be substantial, in terms both of chemical / deployment costs and in lost oil production for the period of the treatment. Same day analysis would prevent treatment more frequently than is actually needed due to uncertainty, leading to cost savings.

Unfortunately, it is usually necessary to transport samples off site for analysis, leading to extra transportation costs and also to delay in the availability of the results. For example, some scale inhibitors can be detected by inductively coupled plasma atomic emission spectroscopy (ICP-AES), which can determine the proportion of a single atom present in a sample. Unfortunately this requires on-shore laboratory facilities, and furthermore is only possible if the chemical being detected contains an atom which is not present in any other components of the produced fluid, for example phosphorus in phosphonate based scale inhibitors. In the case of polymeric scale inhibitors there is often no distinctive atomic species present and it is necessary to use more costly and time consuming methods2. In many cases there may be no simple and accurate test method for detection of a particular chemical. In this instance it may be possible to deduce the presence of a chemical via the behaviour of a fluid, however again this is likely to be time consuming. Finally, the presence of many different chemical species in produced fluids can cause interferences, making it difficult to assess the quantities of each separate component present.

Clariant Oil Services and Haptogen Ltd have developed a detection method that avoids these problems by allowing on-site, same day chemical analysis of aqueous samples. The test method is based on antibodies that specifically bind to a single production chemical molecule, allowing detection of the molecule without interference from other species which may be present in produced water samples.