Chemical Treatments and Usage in Offshore Oil and Gas Production Systems

Abstract

Summary This paper reviews the uses of production treating chemicals, gas processingchemicals, and stimulation and workover chemicals in U.S. offshore oil and gasproduction operations. The purpose, solubility properties, primary genericchemical types, purpose, solubility properties, primary generic chemical types, treatment methods, and typical use concentrations of each chemical group arediscussed. Acute aquatic toxicity data and solubility information arepresented. Introduction The objective of this paper is to examine briefly the broad range ofchemicals used in offshore oil and gas production in the U.S., primarily in the Gulf of Mexico. An important part of this primarily in the Gulf of Mexico. Animportant part of this examination is a presentation of data on acute aquatictoxicity of those chemical constituents that are likely to distribute intoproduced water discharged to the ocean. Most of these aquatic produced waterdischarged to the ocean. Most of these aquatic toxicity data have beendeveloped by chemical suppliers and have not been published previously in thetechnical literature. Evaluation of environmental impact involves factors otherthan the nature and concentration of chemicals added in production operationsand is beyond the scope of the paper. Most of the information and practicespresented are from interviews with technical specialists practices presentedare from interviews with technical specialists from four operating companiesand five chemical suppliers. Considerable attention continues to be focused onthe effects of offshore oil and gas producing operations on the marineenvironment, including the discharge of produced water into the ocean. Removalof produced oil from water has long been recognized as an essential step withstrict standards having been established by the U.S. Environmental Protection Agency (EPA). Present EPA permits do not limit treating chemicals in theproduced water permits do not limit treating chemicals in the produced waterdischarges. Governmental agencies in other areas of the world (e.g., North Sea, Baltic Sea, Mediterranean Sea) are considering preapproval of chemicals thatcould be present in produced-water preapproval of chemicals that could bepresent in produced-water discharges. Constituents of produced water have beenevaluated previously. Middleditch addressed the potential environmental impactof many of the constituents in the produced water. Other studies have focusedon biocides. The effects of various production treating chemicals added toproduced fluids were presented in a report prepared in 1985 for the Offshore Operators Committee (OOC) and prepared in 1985 for the Offshore Operators Committee (OOC) and submitted to the EPA. Investigators in other areas of theworld have shown interest in the environmental aspects of produced waterdischarged to the ocean. The American Petroleum Inst. (API) recently sponsoredan update of the 1985 OOC report, which was expanded to include the broad rangeof chemicals used in offshore oil and gas operations in the U.S. This paper isa condensation of selected portions of that report. Table 1 provides a conciseoverview of the U.S. offshore oil and gas industry. All these numbers wereconsidered preliminary by the sources, subject to revision. The waterproduction data probably have the greatest uncertainty. However, these data areprobably have the greatest uncertainty. However, these data are sufficientlyaccurate to give a good perspective of the industry. It is apparent that a veryhigh percentage of U.S. offshore activity is in the Gulf of Mexico, partialjustification for the emphasis on that area in this paper. Chemicals that maybe used in routine offshore producing operations in the U.S. are included inthe scope of this paper. For purposes of discussion, these chemicals have beenarbitrarily placed into three groups. placed into three groups.The production treating chemicals are those routinely added to the produced fluidsor to seawater or other source water that is injected for waterflooding. Thesechemicals are added for various purposes (such as corrosion or scaleinhibition).The gas processing chemicals are those used for freeze-pointdepression of gas hydrates or for dehydration of produced gas. Hydrogen sulfideand carbon dioxide normally are not produced gas. Hydrogen sulfide and carbondioxide normally are not removed from gas offshore and these sweeteningchemicals and processes are not covered in this paper. processes are notcovered in this paper.The group consists of the stimulation and workoverchemicals, particularly the acids and dense brines, along with their associatedadditives. These groups are discussed more fully later. Production Treating Chemicals Production Treating Chemicals The productiontreating chemicals include biocides, scale and corrosion inhibitors, emulsionbreakers (normal and reverse), coagulants, flocculants, antifoam, surfactants, and paraffin control chemicals. The types and quantities of chemicals used areminimized for both technical and economic reasons. None of the operatingcompanies used all these types of chemicals. JPT P. 604