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Oil in the Sea III: Inputs, Fates, and Effects
For the Gulf of Mexico production facilities operating in the Outer Continental Shelf (OCS) region, MMS tracks the volume of produced water as part of their royalty program. MMS provided produced water volumes in barrels for 1996, 1997, and 1998, reported as a total of (1) injected on lease (i.e., injected back into a reservoir within the lease area), (2) injected off lease (i.e., injected into a reservoir outside the lease area, usually meaning that produced water is piped to another platform for re-injection), (3) transferred off lease (i.e., piped to a central facility for treatment and re-injection), and (4) overboard discharge (i.e., pumped into the water at the platform) (Gail Rainey, pers. comm., 2000). The overboard discharges were used as the volume of produced water discharged into marine waters for the offshore Gulf of Mexico. The DMR data for the Gulf of Mexico are not available in digital format, and the very large number of facilities makes it impossible to review each report to obtain specific data on the oil and grease content. Therefore, a default value of 29 mg/L, which is the maximum amount allowed for the Gulf of Mexico discharges, was used to estimate the maximum amount of oil and grease in offshore produced water discharges in the Gulf of Mexico. Industry operators attempt to keep oil and grease levels below 25 mg/L, so that the maximum will not be exceeded, and many operators are able to achieve levels below 20 mg/L (the long-term average for California was 18 mg/L and for Alaska was 15 mg/L). Thus, 20 mg/L represents the best estimate, and 15 mg/L was used to calculate the minimum estimate for this region. For the calculations, barrels of produced water were converted to liters, then multiplied by 20 mg/L to get mg of oil, that were then converted into tonnes of oil. Produced water discharged an estimated 2,000 tonnes per year of oil into offshore waters (Table D-8).
For the Gulf of Mexico production facilities in coastal waters, referred to as the territorial seas, there is no centralized tracking system. Texas Natural Resources and Railroad Commission (Kevin McClary, pers. comm., 2000) provided a summary of the quarterly reports of produced water volume (in bbls) and oil and grease content (in mg/L) for active dischargers for the fourth quarter of 1999. The volume of produced water discharges in Table D-8 was the total for this one period. The total oil and grease discharges were calculated by multiplying the volume by the oil and grease content for each discharge. For the 29 facilities that reported for this period, the average oil and grease content was calculated as 6.5 mg/L. The calculations were made as for the offshore discharges, that is, bbls of produced water converted to liters, multiplied by 6.5 mg/L to get mg of oil, that was converted to tonnes of oil. Produced water discharged an estimated 4.5 tonnes per year of oil into Texas coastal territorial waters (Table D-8).
For Louisiana territorial seas, the most recent summary of the more than 100 produced water discharges is for 1992, based on analysis of the DMRs. Louisiana Department of Environmental Quality (Doug Hale, pers. comm.) provided the estimate of 510,097 bbls per day of produced water discharges. There was no summary of oil and grease levels, so the best estimate default of 20 mg/L oil and grease was used. The calculations were made as for the offshore discharges, that is, bbls of produced water converted to liters, multiplied by 20 mg/L to get mg of oil, that was converted to tonnes of oil. Produced water discharged an estimated 600 tonnes per year of oil into Louisiana coastal territorial waters (Table D-8).
In California, all oil production occurs in the offshore. Fourteen platforms report produced water discharges (many platforms commingle their produced waters into one discharge point). MMS (Panzer, pers. comm., 2000) provided spreadsheets with the DMR data for the period 1989-1998 that had running means for produced water volume in barrels and oil and grease concentration in mg/L. The actual reported oil and grease concentrations and produced water volumes for each reporting period were used to calculate the total water volume and oil discharges for the region. The calculations were made as for the offshore discharges, that is, bbls of produced water converted to liters, multiplied by 18 mg/L to get mg of oil, that was converted to tonnes of oil Produced water discharged an estimated 85 tonnes per year of oil into federal offshore waters off California (Table D-8).
In Alaska, produced water discharges are reported for fourteen platforms, one tank farm, and one production facility, all discharging into Alaska territorial waters in Cook Inlet. The produced water volumes (in bbls) and oil and grease content, as reported on monthly DMRs for the period January, 1997, to December, 1999, were used to calculate annual averages for that period. For facilities that did not report an oil and grease concentration (e.g., the permit requires only a visual test for sheen), 15 mg/L, the average for all reporting facilities, was used. Produced water discharged an estimated 15 tonnes per year of oil into coastal territorial waters in Alaska (Table D-8).
Petroleos Mexicanos (PEMEX) published an annual report (PEMEX, 2000) describing its achievements in safety, health, and the environment. This report included a section on produced water discharges, stating that 79 percent of the 11.5 million cubic meters produced were reinjected, and reporting a total amount of oil discharged in tonnes. It was assumed that all of the produced water discharges were to marine waters. Using these data, the volume of produced water discharged to the sea in 1999 was calculated to be 15,190,000 bbls. The oil content of produced water (60 mg/ L) was calculated by dividing the reported total oil discharges for produced water by this volume, so there is some uncertainty in this number.
Canada started offshore oil production in eastern Canada in 1996. Produced water volumes, oil levels, and total oil discharges in 1999 were reported in a 1999 discharge summary for the Cohasset Project published by PanCanadian Petroleum Limited. These data for 1999 are shown in Table D-8.