Abstract

In the North Sea, due to the extensive use of water injection for oil displacement and pressure maintenance, many reservoirs experience the problem of scale deposition when injection water problem of scale deposition when injection water starts to breakthrough. In most cases the scaled-up wells are caused by the formation of sulphate scales of Barium and Strontium. Due to their relative hardness and low solubility, there are limited processes available for their removal and the processes available for their removal and the preventive measure such as the ‘squeeze’ inhibitor preventive measure such as the ‘squeeze’ inhibitor treatment has to be taken. It is therefore important to have a proper understanding of the kinetics of scale formation and its detrimental effect on formation damage under both inhibited and uninhibited environment.

In this paper, we will present results of BaSO4 formation kinetics in both beaker tests and in highly reproducible sandpacks which simulates the flow in porous medium. The effect of scale deposition on the porous medium. The effect of scale deposition on the dynamics of formation damage will also be discussed. In the studies of BaSO4 crystal growth kinetics and formation damage, we have included both normal formation/injection brine mixture and the addition of scale inhibitor chemical. There are significant differences in the results of static (beaker tests) and dynamics (core flood) conditions, and between the normal and inhibited brine mix.

Introduction

The formation of mineral scale associated with the production of hydrocarbon has been a concern in production of hydrocarbon has been a concern in oilfield operation. Depending on the nature of the scale and the fluid composition, the deposition can take place within the reservoir which causes formation damage or in the production facilities where blockage can cause severe operational problems. The two main types of scale which are problems. The two main types of scale which are commonly found in the oilfield are carbonate and sulphate scales. Whilst the formation of carbonate scale is associated with the pressure and pH changes of the production fluid, the occurrence of sulphate scale is mainly due to the mixing of incompatible brines, ie. formation water and injection water. In the North Sea, the universal use of sea water injection as the primary oil recovery mechanism and for pressure maintenance means that problems with sulphate scale deposition, mainly barium and strontium, are likely to be present at some stage during the production life of the field.

Apart from its likely occurrence, the relative hardness and low solubility of the sulphate scale means that very few remedial treatments are available for its removal. Processes like acidization which can successfully remove carbonate scale, eg. CaCO3, cannot effectively apply in this case.

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