RIASSUNTO
ABSTRACT:
In the UK, there are strict regulations governing the use of production chemicals in offshore oil and gas fields. Production chemicals are required to have a good environmental profile; during the last decade many harmful products used offshore have been replaced with more environmentally friendly variants. In oil and gas production, corrosion inhibitors are commonly applied to mitigate the corrosion caused by acidic gases (CO2 and H2S) and environmentally friendly products are now widely used in offshore UK oilfields. However, the performance of these products is generally limited by the system temperature. It is commonly accepted that above approximately 90°C (194°F), the efficacy of these products is greatly reduced. Therefore, considering that many new oilfields coming on stream in the UK are hotter than this, there is a necessity to develop corrosion inhibitors that not only perform at high temperature but are also environmentally friendly. This paper details the work performed to develop biodegradable corrosion inhibitors that are effective above 100°C (212°F). The performance of these products in preventing CO2 corrosion in the laboratory environment is discussed.
INTRODUCTION
In oil and gas production, corrosion inhibitors are widely used to mitigate corrosion caused by the presence of CO2 and H2S. Corrosion inhibitors used in oil and gas production can be applied by a number of techniques including continuous injection into the production fluids, batch or squeeze treatment at regular intervals or injected via the lift gas.1 The inhibitors traditionally used are generally nitrogen-containing compounds (amides, amines, imidazolines or quaternary ammonium compounds) and work by forming a protective film on the metal surface that prevents the water from contacting the surface.2 However, these corrosion inhibitors do not normally have a very good environmental profile. They tend to be toxic (LC50 or EC50 values of <1 mg/L) to marine species and are also not readily biodegradable (<60% in 28 days). There are many published examples describing the development of environmentally acceptable corrosion inhibitors.3,4,5 However, there is limited evidence in the literature describing environmentally friendly corrosion inhibitors working effectively at high temperatures. For corrosion inhibitors, high temperature fields can be defined as those with temperatures in excess of 90°C.6 In the UK there are strict environmental regulations that govern the use of production chemicals in offshore oil and gas fields. In addition, more and more oil and gas fields in the UK are being developed that have high operational temperatures. Consequently, there is a need for environmentally friendly corrosion inhibitors which are effective at these temperatures. This paper describes the work performed in developing and testing environmentally friendly corrosion inhibitors for a UK gas/condensate field that is currently in the design stage. This paper is also a continuation of work previously reported.5 An inhibitor is required to mitigate corrosion in a 12-in. subsea, multiphase flow line constructed from carbon steel. The likely operating temperature for the field is between 100 and 120°C, the partial pressure of CO2 is low (1 bar) and the pipeline wall shear stress is also low (5 Pa).