Mercury in Natural Gas - Problems and Technical Solutions for its Removal
Authors: Mussig S. , Rothmann B. 
Published: December 2007

Mercury is known to be present as a trace component in many natural gas reservoirs. As an environmentally hazardous element, mercury has to be removed from the gas stream, preferably on the production site. This removal causes various problems for the operator. First of all the selection of adequate analytical methods to quantify the scope of the problem is important. According to the mercury concentration appropriate removal techniques have to be selected. Due to the presence of mercury in gas, the reservoir fluid also may be affected.

During production and treatment of the gas mercury may be released to the environment and also parts of the plant be contaminated.

Mercury may be emitted to air via e.g. glycol overheads, leading to soil contamination together with incidental spillage during maintenance around the treatment facilities. Materials, which have been in contact with mercury, such as sludge from dehydration units and activated carbon filters applied in gas treatment units are contaminated. Regardless of its concentration mercury is adsorbed on any metal surfaces, in scales and corrosion products, therefore, during maintenance, revamp and abandonment activities all these parts might be contaminated and have to be cleaned or treated prior scrapping and disposal or they have to be disposed off in special ways.

This paper presents the available analytical methods for mercury quantification especially in natural gas and the possibilities to remove mercury from gas streams by applying filters such as activated carbon or by the newly developed amalgamation technique. Finally the possibilities of treating mercury contaminated waste e.g. by applying high temperature processes and the disposal of this waste in abandoned wells is discussed. Several technologies to clean contaminated steel prior scrapping or re-use are presented with special focus on several thermal treatment processes on-site and off-site. Removal technologies from soil are shortly described.

Introduction

Fortunately, mercury is not present in all natural gases, but whenever mercury it is, environmental and technical problems are certain to arise for the E&P company involved. As an environmentally hazardous element, mercury has to be removed from the gas stream, preferably on the production site. After the metal's concentration has been measured by adequate methods, the most appropriate removal technique has to be applied and last but not least mercury and all mercury-contaminated installations, sludge, soil etc. have to be cleaned and the waste has to be disposed of properly and according to the law. All of these processes incure considerable costs and require manpower.

Health hazards caused by mercury have been well known since the middle ages. For that reason adequate precaution methods have to be implemented and staff working on stations where mercury-contaminated gas and waste are handled has to wear appropriate personal safety equipment.

E&P companies in densely populated central Europe are confronted not only with a very stringent health and environmental legislation but also with natural gas reservoirs rich in mercury. Therefore, a high level of expertise on mercury topics has been established over the past decades and this publication is intended to pass on some experience gained during a short journey tracing mercury's path in a gas production facility "from the cradle to the grave", i.e. from reservoir to waste disposal.

Mercury's Origin

Mercury in natural gas is not a man-made nuisance, it occurs naturally in certain gas formations and is inevitably produced with the gas. The mercury traces are supposed to originate from volcanic rocks, often underlying the gas reservoirs.

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