API Publ 4717:2002 pdf download
API Publ 4717:2002 pdf download.Predictors of Water-soluble Organics
(WS0s) in Produced Water- A Literature Review.
The ojectives of this study include:
• Defining the chemical composition and characteristics of WSOs in oil- and gas-well produced water, and identifying the WSOs that interfere with EPA standard methods for total oil and grease; and,
• Identifying reservoir geochemistry, and the physical and chemical characteristics of produced water and crude oil, that may he correlated with WSO concentrations or are indicative of the presence of WSOs in produced water.
This report is a review of the scientific literature on the identity and physical/chemical characteristics of the water-soluble organics (WSOs) in produced water in relation to characteristics of fossil fuels and their reservoirs. The results of this review are the basis for recommendations about the feasibility of developing correlations between WSO concentrations in produced water and physical/chemical properties of the produced waters and/or their reservoirs.
2 Chemical Composition of Produced Water
2.1 ORIGINS OF PRODUCED WATER
During millions of years of geologic time, petroleum and natural gas may accumulate in porous sediments (e.g., sands) trapped between layers of impermeable rock deep within the earth (Collins, 1975). Water may he trapped during millions of years with the oil and gas. This water may be derived from ancient fresh or salt water (connate water) and often is as old as the fossil fuels in the reservoir. When the hydrocarbon reservoir is tapped by a well, the produced gases and fluids may contain connate water. Also, in some oil fields, fresh or salt water may he injected into the reservoir through injection wells to displace oil toward the production wells. Sometimes, this injection water channels through to the production well and is produced with the oil and gas. The water produced with oil and gas is called produced water, produced formation water, or oilfield brine (Neff, 1987, 1997; Black et al., 1994).
Before the crude oil can he refined or the gas processed, the water must be removed. During offshore operations, separation of the produced water from the oil and gas may take place on the production platform or the oil/gas/water mixture may he sent through a pipeline to a shore facility where the produced water is separated from the oil and gas. If not re-injected, the produced water is treated to meet regulatory limits for oil and grease so it may he discharged to the ocean from the platform or from an ocean outfall from a shore-based treatment facility. The current limit for total oil and grease in produced water destined for ocean disposal in U.S. Federal and Upper Cook Inlet, AK, waters is 42 mg/I (ppm) daily maximum and 29 mgI L monthly average (Otto and Arnold, 1996; Veil, 1997).
The oil/gas/water mixture may he processed through devices to separate the three phases from one another. On western Gulf of Mexico platforms, the types of equipment used to remove oil and grease from produced water include, in order of frequency of use, mechanical and hydraulic gas floatation units, skimmers, coalescers, hydrocyclones, and filters (Otto and Arnold, 1996). Chemicals may he added to the process stream to improve the efficiency of oil/gas/water separation. Even with the most advanced separation equipment, the oil/water separation is not IOO% efficient. If the oil/water separation system is efficient, however, most of the chemicals remaining in the treated produced water are in solution or colloidal suspension in the water.
To prevent corrosion, foaming, scale formation, hydrogen sulfide formation, and bacterial growth, or to improve the efficiency and completeness of oil/water separation, small amounts of specialty chemicals may he added to the production stream at different steps in the production and treatment process (Hudgins, 1989, 1991, 1992). Most of these chemicals remain in the oil or gas phase; others are water-soluble, remain in the produced water, and are discharged. Approximately 19% of the offshore production chemicals used on platforms in the North Sea are discharged in treated produced water, including more than 500/0 of the emulsifiers, surfactants, oil removing agents, and scale inhibitors (van Hattum et al., 1992; Ynnesdal and Furuholt, I 994; Hudgins, 1 994). Only small amounts (less than 20% of the amounts used) of corrosion inhibitors, oxygen scavengers, emulsion breakers, defoamers, and gas treatment agents are discharged with produced water.
