Upgrading Production Facilities on the Funan Platform to Remove Hydrocarbons and Heavy Metals from Produced Water

Abstract

Abstract Unocal Thailand has been producing natural gas in the Gulf of Thailand since 1981. In recent years, with increasing natural gas production, the volume of produced water has also been increasing. Contaminants in the water include hydrocarbons and heavy metals. The original platform design did not contemplate the need to handle and remediate high volumes of produced water. Characterization of the produced water determined that hydrocarbons were present as stabilized emulsions, mercury was present in elemental form, and arsenic was present in water soluble form. The objective is to reduce contaminants in the produced water to the following levels: Hydrocarbons to < 40 PPM, Mercury to < 10 PPB, and Arsenic to < 250 PPB. In 1995, Unocal Thailand initiated a program to upgrade water handling facilities on its central processing platforms. On Funan, this involved upgrades to the high pressure inlet separators, improvements to the original skim tank, and the installation of hydrocyclones as well as induced gas flotation equipment. The latter were required along with additional facilities to treat the water for heavy metals removal. The vessel upgrades are described in this paper along with a review of the complete water cleaning train. Operational data illustrating the performance of the Unocal Thailand Water Cleaning Process are also presented. Introduction Unocal Thailand, a subsidiary of Unocal Corporation, produces natural gas and condensate from nine fields in the Gulf of Thailand. Since 1981, Unocal has drilled over 1000 wells. Production from 60 remote wellhead platforms and is s pipelined to four production and four central processing platforms. In 1997 Unocal Thailand natural gas production averaged 970 MMSCFD while accompanying liquid hydrocarbon (condensate) production averaged 34,600 bbls per day. Figure I illustrates how fluids flow from the remote platforms to the production and central processing platforms. Also in 1997, Unocal Thailand platforms produced an average of 35,850 bbls of water per day. However, with the introduction of new gas production technology and new development strategies, the volume of produced water is expected to increase over the next 2 years to as much as 75,000 bbls of water per day. To ensure that all future Thailand national environmental discharge regulations are observed, Unocal Thailand has, over the past three years, developed, tested, and installed technology for removing contaminants from co-produced water. The goal of the Unocal water-cleaning project was to reduce the levels of these contaminants in overboard discharge water to the following (1):Mercury ? 10 PPBArsenic ? 250 PPBHydrocarbons ? 40 PPM Where feasible, Unocal Thailand is pursuing a "zero discharge" philosophy which entails re-injecting co-produced water back into the formations from which it originated. Unfortunately, the re-injection of all produced water is not feasible given the large geographic area over which gas production occurs. Thus the development of surface cleaning technology was also necessary. This upgrade project increased the produced water handling capacity on Funan from its original design limit of 4800 BWPD to the new target level of 25,000 BWPD. Also, all installed equipment had to be compatible with the chemistry required for heavy metals removal.