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Environmental Chemistry Case Studies |
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Seabed Surveys for Oil Exploration/Production In the current climate of environmental awareness and accountability, the impact of drilling operations on the environment has become a major focus for oil companies. GEOTECH frequently carries out analyses of seabed samples. These samples are analysed to determine a number of physical and chemical properties, including total petroleum hydrocarbons (TPH) (detection limit: ~ 20mg/kg), trace metals, including barium, cadmium, chromium, mercury and lead (detection limit: 10-50,000 mg/kg), particle size, total carbon (TC) and total organic carbon (TOC). The analyses provide an indication of the concentration of these compounds in an undisturbed natural setting. Companies often commission a base survey (conducted before drilling commences) and later analyse the same site to provide information as to the extent (if any) of possible contamination. Study of Wood Samples from Offshore Ship Wrecks The Maritime Museum of Western Australia commissioned GEOTECH to analyse a suite of wood samples from wrecks in the Indian Ocean. Pyrolysis gas chromatography-mass spectrometry (Py GC-MS) was used to distinguish the various stages of biodegradation in these samples, and the data were used to help select the appropriate preservation technique. Investigation of Production Problems in a Fractured Reservoir GEOTECH was asked to characterise an unknown slime (affectionately called "gloop") recovered from a hydrocarbon production well. This "gloop" was thought to be blocking stimulated fractures and preventing the production of commercial quantities of crude oil. The analytical programme was designed specifically for the client, including tests to determine the composition of the "gloop" and the reason for its formation. Once thses factors were determined, an antidote was developed to prevent the "gloop" from forming downhole, and the well resumed commercial activity. Leachate Testing Oil companies and other clients often need to assess the nature of sediments to be disposed of in respect to landfill criteria, as per Landfill Waste Classification and Waste Definitions. In a first testing phase the concentration of contaminants such as BTEX, TPH and metals in the waste are determined according to ASTM methods. These contaminant concentrations are compared with contaminant thresholds (CT) values and the contaminant assigned a classification. If any contaminant concentration exceeds the relevant CT value, Australian Standard Leaching Procedures (ASLP) leachate concentrations for all relevant contaminants are determined. GEOTECH regularly performs ASLP leachate analyses on sands recovered during shutdown of oil production wells on the North West Shelf to allow operators to dispose of the sand according to legislative requirements. Biodegradation of Base Fluid As the environmental impact of offshore drilling becomes increasingly important, exploration companies are starting to use synthetic base fluids that, when discharged, may have an impact on marine eco-systems. These base fluids reside in cuttings piles on the seabed below the platform or mobile rig. As these piles are largely oxygen starved, it is important to be able to determine the rate of anaerobic biodegradation of these base fluids in conditions that are similar to those found in the off-shore environment. Anaerobic biodegradation is an important factor for reducing the impact of multi-well platforms that create a larger cuttings pile. In a recent investigation for an overseas client, the anaerobic biodegradation of three base fluids were tested. A closed bottle anaerobic biodegradation protocol was developed to monitor the biodegradation products associated with anaerobic biodegradation. Initially ISO 11734 was used as a reference for the project, however, various modifications were incorporated into the protocol to ensure more robust, comparative results. Oil Mist Monitoring A recent project on the North West Shelf of Australia was undertaken to investigate the exposure of staff to synthetic based muds (SBM) in a mud handling area of an offshore oil rig. Much of the equipment in this area, eg. shakers, centrifuges etc, has the potential to produce airborne hydrocarbons in the form of oil mist/vapour. Appropriate sampling points were chosen to represent a cross section of the environment encountered by personnel working in these rooms. Background levels were determined when the pits contained the SBM, but before drilling started. Sets of samples were taken over 24 hours while drilling. Air temperature, humidity and mud temperatures were recorded during sampling time. The analysis was performed using the current international standard methods which involved specialised sampling equipment for simultaneous collection of oil mist and vapour (NIOSH 5026, ASTM D3687). Vapour samples were actively collected on carbon tubes and passively collected on carbon "Radiello" tubes in accordance with methods detailed on the Radiello website: http://www.radiello.com/english/index_en.html |
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