AU2011100069A4 - Superior Geothermal Well - Google Patents

Description

Australia Patents Act 1990 Complete specification Innovation Patent Superior Geothermal well 1. Description The following statement is a full description of this invention including the best way of utilizing the invention known to us. The invention is an improved geothermal well using fluid as a heat transfer medium in a closed loop whereby the continuously circulating fluid transfers heat from a naturally occurring geothermal heat source within the ground to the surface. The invention will provide a simpler and more cost effective means of extracting geothermal heat than is obtainable using other methods. The following statement is a full description of this invention, including the best method of operation known to us. Historically all subsurface geothermal wells work on the principle ofpumping water into an injection well and recovering heat by retrieving a volume of water from the producing well. Heat is removed at the surface by heat exchange and is available for commercial use. The system is a circulation system using two wells. This invention utilizes one well only to transfer heat from the subsurface reservoir to the surface. The heat transfer system of the invention is powered by geothermal heat and does not rely on mechanical pumping devices as do some other systems for the transfer of hot fluid to the surface and also for injection of the fluid to the reservoir in the injection well. Organic or inorganic liquids or a mixture of liquids with special properties, are claimed in the invention to maintain circulation utilizing geothermal heat as the driving force. The Primary mode of circulation will operate under the principle of thermo siphon resulting from the different densities of the hot fluid generated at the bottom of the hole and the coolfluid generated after heat is extracted at the top of the hole. Accordingly, afluid flow will be Page l l established as a result of the buoyancy effect. A low powered pump is included in the system to insure circulation at all times. The pump is not the prime mover of the fluid but included as a form of insurance so that even under the most adverse conditions circulation will be maintained. The invention has been especially devised to provide a simple cost effective low maintenance solution to geothermal heat production particularly in Australia where geothermal gradients are less than countries which are geologically favoured with higher geothermal gradients. Page 1 2

Claims (4)

1. 2. Claims Claims defining the invention are as follows: 1. A one well design which extracts heat from the ground by circulating hot fluid from the bottom of the hole to the top of the hole. Heat is extracted from the fluid at top of the hole and the cooler fluid is returned to the bottom of the hole in a perpetual cycle. The main circulation mechanism is the thermo siphon effect, this is a mechanism whereby the difference in density of the fluid between the cooler fluid at the top of the well and the hotter fluid at the bottom of the well results in a density imbalance which in turn generates fluid flow. 2 Simple design: The geothermal well design is shown in the Diagram Fig-L A geothermal well design as claimed in claim 1, for which a hole is drilled into the ground (h) such that the bottom of the hole is at least as deep as the base of the target heat reservoir (e). Steel casing (a), of lesser diameter than the hole with a sealed bottom end (i), is inserted into the hole(p), and sealed in the ground with cement (d). Steel tubing (b) of lesser diameter than the casing, is inserted into the casing such that there remains a space between the base ofthe casing (i), and the bottom end of the tubing j). A closed loop system is maintained by connecting the return pipes (k) to tubing (b) via a circulating pump (f). a circulating fluid is introduced into the system via fluid inlet (L). Valve (m) is closed. Valve Bleed (n) is open. Fluid is pumped through the system displacing the fluid that was originally in the system. Fluid is circulated until all the air (or originalfluid) is purged and the introduced fluid completely fills in the system. Appropriate pressure in the system must be maintained at all times to ensure that the introduced fluid remains in the liquid phase throughout the system If the Temperature of the liquid at the bottom of the hole (T) is higher than the temperature of the cooled fluid then the cooled fluid (Cc) will descend down the tubing and the hot fluid Ch) will rise up the annulus as a result of the different densities between the cool and hot fluids. The circulation rate will depend on the depth of the well, the geometry of the pipe work and the difference between the bottom and top hole temperatures.
2. 3. Fluid performance. A geothermal well design as claimed in any claim 1 and 2, wherein any liquid or combination of fluids can be used. The inventor recognizes that certain fluids have special properties which will result in more efficient heat transfer than others.
3. 4. Pump as prime mover not required. A geothermal well design as claimed in any of claims 1 to 3, which relies on the thermo siphon Page | 3 effect for circulation, into which a pump is included in the system for both maintenance (addition offluid or withdraw offluid or pressure adjustment) and also to adjust the flow rate to an optimum level if necessary. The invention is different to all other systems in that reliance on a pump for circulation as the prime mover is not necessary.
4. 5. Maintenance. A geothermal well design as claimed in any of claims I to 4, wherein moving parts are virtually eliminated. The system is a closed system, and reservoir fluids do not intrude into the system which sets the invention apart from all other systems. Page 4