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AAPG European Region, 3rd Hydrocarbon Geothermal Cross Over Technology Workshop

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Utilizing Existing Deep Wellbores As Heat Exchanger Wells


Abandoned deep wellbores are very common, tens of thousands of these holes can be found across each country in the world. Some are results of unsuccessful hydrocarbon explorations, others are depleted hydrocarbon wells, not to mention those drilled for geothermal purposes but ended up unused for some reason. To get rid of these wells its often causes difficulties to their owners. Each country has its own legislation regarding well abandonment, but one factor is universal, it is expensive. Either unsuccessful or depleted all these wells share an important parameter: the temperature. And this temperature can be transformed into energy with a new method, such as dual string well completion. Heat pump based geothermal systems are already in everyday use in shallow wells with depth less, or about 100 meters (typical temperature range is in between 15-30 degrees Celsius). In these wells, a few degrees Celsius temperature difference can heat up or cool down a family house sized building. Much larger temperature differences can be utilized from deep wellbores. 70 to 100 degrees Celsius can easily be found in holes which were initially drilled in hydrocarbon explorations or for geothermal purposes, and which are deeper than 2000 meters. Regarding the indicated technology, it is flexible enough to be set in almost every cased hole. The technology in nutshell is, that the circulating fluid is injected down in one of the tubings, and it will collect heat through a downhole heat exchanger (DHE) at the lower section of the well. After it is heated up it is circulated to the surface through the other tubing string. The temperature difference between the inflow and outflow line can be utilized in several ways. Since this is a low enthalpy petrothermal system, direct use for heating is the most efficient way to use the recovered heat. The system can be connected to a surface heat exchanger in order to use the heat energy or could be converted into electricity applying appropriate surface technology. The efficiency of the system principally depends on the chosen fluid circulated in the well! The gained heat can be maximized using the most suitable fluid, optimal circulation rate, coated up-flowing tubing and fit- for-purpose downhole heat exchanger. The heat transfer system is in a closed circulation loop, without any formation water production. With this presentation the audience will gain insight into the possible exploitation of low enthalpy petrothermal system using existing deep wells (deeper than 2000 m), including the amount of energy that can be gained with the method and the achievable technology. Circulation models will be presented, as well, to address the importance of the above-mentioned items of the system and to demonstrate the economic potential.