Chemical Use in North Sea Oil and Gas E&P

Abstract

Summary In May 1990, the Norwegian Oil Industry Assn., Oljeindustriens Landsforening (OLF), commissioned a survey of chemical use in E&P activities in the North Sea. Ten operating companies and six chemical suppliers provided data on the specific types and quantities of chemicals used in their operations and the properties of those chemicals. These companies operated or supplied chemicals in the Norwegian, British, and Netherlands sectors. Technical discussions on the reasons for using chemicals and their application also were held. The comprehensive results of this survey are available from OLF as a report, with all chemical data on disk. This paper summarizes the primary observations from the OLF report. The quantitative uses are compared with previous summaries of quantities of chemicals used. Probable discharge quantities and concentrations are discussed. Acute aquatic toxicity data submitted by participants are presented and practical aspects discussed. Objective The objective of this paper is to summarize oil and gas E&P activities in the North Sea in terms of the chemicals used in various operations. The potential impact of discharged chemicals on the environment is of interest to companies, governments, and people around the North Sea. This paper condenses the OLF report.1 That report examined the purpose, chemical nature, properties, and treatment methods for this broad range of chemicals in more detail than feasible for this paper. Tables summarizing the data on quantities of chemicals used, discharged, and injected are included in this paper. The Appendix covers important environmental aspects (including reported acute aquatic toxicity data of chemicals). Scientific and trade literature and government publications were used to prepare the report, but the main sources of information were the companies participating in the survey. Scope Chemicals that may be used in "routine" offshore E&P activities in any of the five sectors of the North Sea were included in the OLF survey. Chemicals used in construction activities were excluded. Norway, the U.K., The Netherlands, Denmark, and Germany collect data on offshore drilling and production and the chemicals used and discharged into the North Sea. The data are submitted to the Paris Commission (Parcom), an intergovernmental agency acting on a broad range of items affecting many European countries. Chemical-use data are categorized by function groups for reporting to Parcom; identical or similar groups were used in the OLF survey. Subgroups and a new general class for cement, stimulation, and workover chemicals were added to the survey. The survey focused on the three largest sectors: Norway, the U.K., and The Netherlands. The participation of 10 operators and 6 suppliers active in all three sectors provided a sound basis for accurately describing major North Sea practices. The participating operating companies produced about 53% of the oil and 61% of the gas and drilled 29% of the wells in the North Sea in 1989, the year covered by the OLF survey. Overall Chemical Use Chemicals are used for a number of different purposes in offshore oil and gas drilling and production. These chemicals usually are used only to prevent operational problems, as discussed in detail in the OLF report. Alternative technology is being used in many instances when appropriate, but the use of chemicals is often necessary. Required treatment concentrations are usually minimized, based on chemical testing and operating experience in the specific system being treated. Oil industry operations generally are organized into drilling and production activities, with the Parcom data grouped similarly. Three broad, general observations can be made from the 1987 Parcom data and the 1989 data submitted by operating companies participating in the OLF survey (Table 1). These data do not include cement, stimulation, and workover chemicals.Far more drilling chemicals than production chemicals are used.A larger percentage of drilling chemicals than production chemicals are discharged.The percentage of discharged values in 1987 and 1989 agree for drilling, but there appears to be an increase for production chemicals in 1989. However, changed reporting requirements may be responsible for this apparent difference. Reporting the total quantities of chemicals used and discharged for the entire North Sea would be useful. Unfortunately, values for both use and discharge are not available from either 1987 or 1988 Parcom data, and 1989 Parcom data were not yet available. The 1987 Parcom data are reasonable approximations of total North Sea chemical use and discharge for that year. The two estimations should not introduce any major uncertainty in total values. The values of total 1989 use and discharge can be estimated from the survey data using reasonable bases for proportioning.Participants drilled about 30% of the wells, suggesting that total drilling chemical use would be about 490,000 tonnes, about 50 % more than in 1987.Participants produced about one-half the oil in 1989, suggesting that total use of production chemicals would be about 40,000 tonnes. This represents an increase of about 33% over 1987. Use and discharge of chemicals from various groups are discussed separately. Environmental aspects for all groups are presented in the Appendix. Drilling Chemicals Both water-based muds (WBM) and oil-based muds (OBM) are used in North Sea drilling. Chemicals must be added to these muds frequently to maintain the required chemical and physical properties. WBM may contain large amounts of dissolved salts and various concentrations of many other additives. Seawater muds, KCl/polymer muds, saturated saltwater muds, and lime muds are WBM, as are a dozen or more other variations. WBM are continually being prepared, treated, and discharged during drilling. Essentially all the WBM used in drilling a well are discharged, except for the small amount left behind casing during cementing.