Treatment and Disposal Options for NORM Oil Field Waste

Abstract

Abstract Treatment and disposal options by Shell Offshore Inc. were shown to reduce effectively NORM waste volumes. Options included scale prediction and inhibition programs, chemical dissolver treatments, minimization through dewatering waste stream segregation, and on-line vessel cleaning operations. Offshore subsurface injection of NORM waste by the producing operator has been demonstrated for the past four years to be a cost-effective alternative to commercial-site disposal. Introduction Naturally Occurring Radioactive Material, NORM, represents primarily the radionuclides of the decay chains of the two long-lived isotopes Uranium 238 and Thorium 232. These Naturally Occurring Radionuclides (NORs) are generally produced to the surface together with produced fluids (gas. oil, water) and/or solids. There are two common types of NORM materials that are found in oil and gas production facilities. These are the Radon-based NORM that is frequently found in natural gas facilities and is dominated by thin layers of Lead 210 deposits and the Radium-based NORM that is found in oil-producing fields and is predominantly made of Radium-226 and Radium-228 and their progeny. The Radium-based NORM is usually generated when Ra-226/Ra-228 co-precipitate with scale-forming cations during the mixing of formation water (containing Ba, Ca, Sr, Ra, and other ions) with seawater (containing sulfate ions). This scale deposits in the interior surfaces of downhole tubing, valves, pumps, vessels, flowlines, and manifolds and accumulates in the sludge in separators and tanks. NORM waste generally contains small quantities of the radioactive scale and is characterized by low radioactivity, ranging from background level to several thousand picoCuries per gram, pCi/g. The other components of the waste are commonly sand, organic solids (paraffins/asphaltenes), corrosion products, biomass, and water. Since the cost of disposal depends on the volume of the waste, the industry has been investigating various technologies to reduce significantly this volume. These technologies include solvent extraction, physical separation of liquids from solids, chemical dissolution of the NORM, chemical inhibition, and cost-effective disposal options of the various phases of these processes (surface and subsurface). This paper will discuss only the Radium-based NORM and will focus on Shell's experience in (1) detection, (2) treating. and (3) disposal of NORM waste from Gulf of Mexico operations. Performance of the various technologies that were applied will be summarized. These include inhibition of scale formation, chemical treatment, and deepwell disposal. Field case histories will be discussed and the developed best practices for management and disposal of NORM will be outlined in view of the new environmental concerns and regulations. Background Handling and disposal of NORM waste has been managed by the oil and gas industry using various approaches and utilizing several processes. Handling has primarily involved hydro-blast cleaning and containerization in drums of the liquid/solid waste streams. P. 155