Application of magnetic susceptibility measurements to oilfield scale management
Imhmed, Salim Algadafi Ali
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The management of a petroleum reservoir requires good understanding of the geology and the properties of the reservoir. This understanding can be obtained from the analysis of results of down-hole tests and laboratory measurements. One of the properties that can be measured is the magnetic behaviour of the reservoir fluids and mineral scales. The build-up of scale is an important process in oil and gas reservoirs, and can have a damaging effect on the flow of fluid in reservoir rocks and in wells. An understanding of the magnetic properties of fluids such as brines, crude oils, brines with a scaling tendency, brines containing scale inhibitors, and of scale minerals is a key objective of this research. These magnetic techniques have the advantage of being environmentally neutral, nondestructive, rapid and low cost (Potter 2005). Understanding of the magnetic properties of the petroleum reservoir matrix rock may provide new techniques for improved reservoir characterisation, petroleum exploration and production. Magnetic susceptibility measurements of brines, crude oils and scale inhibitors have been carried out and are reported in this thesis. All fluids are diamagnetic, with distinct differences between them. The magnetic susceptibility values for brines are related to their solute composition, while for crude oils the magnetic susceptibility values are related to their physical and chemical properties. The effect of solute composition and concentration on the magnetic susceptibility of a brine is also measured. Measuring the magnetic susceptibility of a produced water sample would allow rapid detection of injection water breakthrough at the production facilities, and therefore iii improve the prospect of quickly deploying a preventative or remedial action to mitigate the risk of inorganic scale damage in the production system. The proposed method described herein introduces the potential for either an in line system, or at least an immediate analysis of the sample when captured, thus allowing operators to make important scale management decisions much earlier than is currently possible. Magnetic hysteresis measurements of reservoir scale minerals could be used as a rapid, non-destructive method to characterise and indentify the types of scale minerals occurring (diamagnetic, paramagnetic, ferromagnetic and antiferromagnetic). Changes in the slope (the magnetic susceptibility) of the hysteresis curves may be used to identify different scale minerals. Straight lines with negative slope are due to diamagnetic minerals, whilst straight lines with positive slope are due to paramagnetic minerals. The relative amounts of diamagnetic and paramagnetic minerals contained in a mixture of the two can potentially be quantified by the slope of the straight line at high fields.