Low Temperature Geothermal for Offshore Use

Geothermal energy is a baseload power generation system which uses the high temperature of the deep layers below the Earth’s surface. It has traditionally relied on very high temperature wells, usually at temperatures over 180°C, but no less than 100°C (Ref 5). The largest geothermal plant in the US, The Geysers Plant in California, uses steam that is over 250°C (Ref 4). The systems are costly and available locations limited by the depth required to achieve these temperatures. Using organic Rankine cycle technology much lower temperatures can be and are used to generate electricity. Ocean Thermal Energy Conversion (OTEC) famously runs on a 20°C temperature difference, with the hot side being about 25°C and the cold side being 5°C or colder. This paper will provide a practical design and thermodynamic analysis of a system designed to run at no more than 100°C. This is a temperature that can be encountered at a reasonable depth onshore and offshore. In the Gulf of Mexico many of the legacy reservoirs are hotter than this (Ref 6). Offshore we will also take advantage of the immense heat sink that is the ocean. The system will utilize well derived heat and cold water to run a power cycle. It is expected that low temperature geothermal will be a practical source for offshore baseload power. One possible use is to power oil and gas platforms, which as they transition need green energy. Unlike wind offshore geothermal will not need battery backup, and once the field has played out, geothermal can then be used to supply power to shore or other nearby platforms. Novel/Additive Information: The system will use both novel well configurations and a novel organic Rankine cycle system for power.