Chemical Treatments and Usage in Offshore Oil and Gas Production Systems

Abstract

ABSTRACT The use of chemicals in U.S. offshore oil and gas production operations are reviewed. The discussions cover the production treating chemicals, gas processing chemicals, and stimulation and workover chemicals. The purpose, solubility properties, primary generic chemical types, and typical use concentrations of each chemical group will be briefly discussed. Acute aquatic toxicity data and solubity information provided by the chemical suppliers are presented for 'the production treating chemicals, including biocides, scale and corrosion inhibitors, emulsion breakers, etc. Aquatic toxicity data for the gas processing chemicals (methanol glycoIs) were primarily obtained from the literature. A portion of these chemicals will dissolve in the produced water, with the remainder being distributed into the oil. Most of the water produced with oil and gas in offshore operations in the U.S. is treated to remove dispersed oil and grease, then discharged to the sea. The discussion on environmental aspects summarizes information on the aquatic toxicity, solubility, and typical treatment and discharge concentrations for chemicals used for each purpose. Actual environmental impact must include site specific factors, such as water depths, currents, temperature, etc., which are outside the scope of this paper. INTRODUCTION OBJECTIVE The objective of this paper is to examine briefly the broad range of chemicals used in offshore oil and gas production in the U.S. An important part of this examination will be a presentation of data on acute aquatic toxicity of those chemical constituents which are likely to distribute into produced water being discharged to the ocean. Most of this aquatic toxicity data has been developed by the chemical suppliers and has not been previously published in the technical literature. Evaluation of environmental impact involves factors other than the nature and concentration of chemicals added in production operations and is beyond the scope of the study. Most of the information and practices presented are based on the results of interviews with technical specialists with four operating companies and five chemical suppliers. BACKGROUND Considerable attention continues to be focused on the effects of offshore oil and gas producing operations on the marine environment. One aspect being examined is the discharge of produced water into the ocean. Removal of produced oil from water has long been recognized as an essential step with strict standards having been established by the Environmental Protection Agencyl,2,3. Present EPA permits do not limit treating chemicals in the produced water discharges. Governmental and intergovernmental agencies in other areas of the world (e.g. North Sea, Baltic Sea, Mediterranean Sea, etc.) are considering preapproval of chemicals that could be present in produced water discharges. Constituents of produced water have previously been evaluated. Middleditch4 addressed the potential environmental impact of many of the constituents in the produced water. Other studies have focused on bi0cides.5,6 The effect of various production treating chemicals added to produced fluids was presented in a report prepared in 1985 for the Offshore Operators Committee (OOC) and submitted to the EPA7 Investigators in other areas of the world have shown interest in the environmental aspects of produced water discharge to the oceans8. The American Petroleum Institute (API) recently sponsored an update of the 1985 OOC report, which was expanded to include the broad range of chemicals used in offshore oil and gas operations in the U.S.9,10. This paper is a condensation ofse