RIASSUNTO
Abstract
Unocal is the largest producer of natural gas in the Gulf of Thailand. Unocal is faced with finding the most cost-effective way to handle produced water from its oil and gas operations to minimize its impact on the environment. Two options were considered for handling the water: water treatment and water re-injection. This paper looks at the re-injection option and its history and future considerations as it pertains to the Erawan Field.
The promising results from early injectivity tests and long term availability of depleted wells have led to full-scale implementation of water re-injection at the Erawan Field. Water re-injection performance begain at 80% of total Erawan produced water and has improved to 92% due to improvement in facility design and overall operating efficiency. Action items have been developed for the immediate, medium and long-terms and incorporated into Unocal Thailand's business unit plan.
Typical water injection wells are described as well as good injection well candidates. Erawan Field has 5 major water injection facilities located at each processing platform with bridge connected wellhead platforms. In addition, water is re-injected at 7 remote wellhead platforms utilizing separator pressure vs. aid of an injection pump. Presently, Erawan is re-injecting approximately 20,000 BWPD in 30 wells located on the 12 platforms. Water disposal capacity from the depleted gas wells is estimated at 100+ MMBW. This is equivalent to 15 years of water disposal.
Topics to be covered in this paper will be lessons learned, anticipated well characteristics, water management history and future considerations for water re-injection at the Erawan Field.
Introduction
Unocal Thailand, as a major oil and gas exploration and production company, has been proactive in dealing with the environmental impact of oil and gas production operations. Monitoring on heavy metal and dissolved hydrocarbon content in effluent had long been performed. Since 1996, mercury studies have been conducted in the vicinity of gas processing platforms and remote wellhead platforms in order to detect and measure mercury levels in fish and sediment1. The findings have been evaluated both internally and by external consulting firms. As a result, Unocal began several pilot tests in various processing locations to determine the feasibility of either water treatment or water re-injection to address the future environmental impact from heavy metals or other contaminants. In 1997, these pilots led to full-scale implementation of water re-injection disposal at both remote wellhead and processing platforms in the Erawan Field while other facilities proceed with chemical treatment process.
Water re-injection has long been utilized in waterflood technology as well as a means of waste disposal for both sludge and produced water. Water re-injection is believed to be the best solution for disposal of produced water in an attempt toward zero discharge and to prevent generation of byproducts from the treatment process.