Anaerobic microorganisms which are frequently associated with corrosion fail Control of bacterial activity are posing major challenge in Saudi Arabia's massive seawater flooding systems. Biocides are used to control bacteria throughout the oil industry. A study to explore the feasibility to develop a detection technique for biocide batch treatments, preferably on-line and in real time, for their potential use in seawater flooding system network is described. Several methods to measure key components of the biocide composition were investigated in the initial stage. Three different techniques were explored during the feasibility phase study to detect and measure concentrations of biocide in seawater. This helped our plans for designing a sensor based on such detection techniques. The techniques explored were to monitor change in temperature, change in pH, and change in chromophore concentration (colorimetric) in the enzymatic reaction.

The investigated methods included the use of acetylcholine esterase, based on the pH change as a result of acetate formation, the production of reaction heat (thermal) or on the colorimetric detection of the chromophore concentration based on the conversion of acetylthiocholine in combination with a chromophore. It was found that the colorimetric system was the most versatile system to perform the measurement to be able to show the feasibility of the method in real sea water samples and to demonstrate the effects of the biocides on the measurement system.

1.0 Introduction

In water flooding systems, deoxygenated and filtered seawater is injected at strategic points along the periphery of the oil reservoir, displacing the oil and "pushing" it toward oil supply wells in the center of the formation. The technique enhances crude oil recovery substantially and allows for greater returns from the field.

The seawater flooding system in Saudi Arabia is the largest of its kind in the world. It is deoxygenated water and treated with various organic biocides mixtures. The short duration, high concentration batch biocide treatment is designed to prevent the growth of bacteria in the system, thereby minimizing biofouling, water quality deterioration and Microbially Influenced Corrosion (MIC).

Since the system's size is massive, it is very challenging to detect the arrival of a biocide slug treatment at the far water injection wells. Furthermore, quantification of biocide residual concentration in 'real time' at remote desert locations is not currently possible. Developing sensor technologies, which will quantify biocide residual concentrations hundreds of kilometers from the biocide injection location without manual sample collection and conventional wet chemistry analysis, is challenging.

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