The Evaluation of a New Environmentally Friendly Combined Product for Application in the North Sea for Effective Scale and Corrosion Control

Abstract

The introduction of more stringent environmental regulation within the North Sea has resulted in increased focus on developing environmentally acceptable inhibitors for application to oil and gas applications. One approach in fulfilling these criteria has been the emergence of multifunctional combined products. This paper demonstrates how this approach can be used effectively to control both scale and corrosion problems. A new environmentally friendly product was developed within the laboratory that gave improved scale control performance against conventional products while also affording excellent corrosion control. A series of tests were conducted to establish the performance of the product as well as compatibility with produced fluids from a North Sea platform. The results of the laboratory investigation are discussed in detail including the advantages and disadvantages offered by this approach as well as the potential environmental benefits. Introduction The North Sea is a mature region where continued economically viable oil and gas production has resulted in a number of technical and logistical challenges. Not least of these is extending the life of production wells to maintain hydrocarbon recovery while addressing issues of design life and changing production conditions(1). Two areas of particular importance are corrosion of pipelines and the topside facilities and the formation of mineral scale due to the large amounts of water used and co-produced with hydrocarbons(2,3). Carbon steel is extensively used in the petroleum industry for both pipelines to transport the hydrocarbons to shore for processing and in the offshore topside facilities. This grade of steel has an inherently low resistance to corrosion, but due to the potential Capex savings and other associated economic issues, is the material most commonly utilised. However, oil and gas production is accompanied by a number of potentially corrosive environmental factors including differing amounts of water with varying concentrations and types of salt, CO2, H2S, organic acids, as well as liquid hydrocarbons(4). These factors combine to give rise to a particularly aggressive environment, where corrosion can be rapid and severe. A review of the literature yields numerous cases of corrosion failures with the associated loss in production and revenue this can cause(5,6). A further concern, most notable in the North Sea, is the problems encountered in production due to the formation and build up of scale(7). As the water cut in mature fields increases and greater quantities of seawater are re-injected to maintain reservoir pressure so the problems of scale formation increase. This can lead to blockages in valves and a steady reduction in the pipe carrying capacity. This can eventually result in full suspension of production while essential maintenance is conducted which is an extremely costly exercise. The formation of scale can also influence localized corrosion depending on the nature and type of scale formed and several other factors including, pH, pressure and temperature(8). The majority of producing wells where scale formation is an issue are treated by chemical means(9). A range of scale inhibitors have been developed over the years with particular physical and chemical properties developed for specific field applications(10). This type of chemical solution is also widely utilized in corrosion control, and like scale inhibitors, are designed to be system specific. These offer the benefit of being relatively inexpensive compared to corrosion resistant alloys (CRA's) while allowing the design life of the facility to be extended.