|2021-03-03 来源： 中国石化新闻网|
王佳晶 摘译自 今日油价
Can Abandoned Oil Wells Be Used To Generate Geothermal Power?
“The decade of geothermal” is a phrase that is becoming increasingly common in media and energy industry gatherings as the international zero-emission push comes to include one of the most fascinating—and clean—ways of extracting energy from the earth: geothermal power.
To reach the heat that the mantle of the Earth radiates into the core, geothermal companies need to drill—and they need to drill deep. In fact, one of the biggest challenges for this emerging industry is drilling deep enough to get to the really high temperatures: drilling so deep is risky and costly.
Yet geothermal can do pretty well even at smaller depths. According to a recent analysis by Rystad Energy, to generate electricity from the vaporized water heated up in geothermal wells, a power generation facility needs temperatures of 240 to 300 degrees Celsius. The analysis adds that as much as 70 percent of geothermal output right now is used for electricity generation.
Indeed, with the urge to electrify everything—whether this is wise or not—it’s all about electricity and, more specifically, emission-free electricity. Geothermal is perfect for this: while the drilling of a geothermal well does involve equipment that uses fossil fuels, from a lifetime perspective, geothermal is fully comparable with wind and solar, which are also not entirely emission-free given the materials they need to operate.
Yet geothermal has been slow to take off because of the high upfront costs and the general uncertainly about the result of drilling. Industry experts invariably note that the heat is everywhere beneath us, but they also make a point of emphasizing that not all of that heat is that easy—or economical—to reach. Iceland is always a case in point with its easily reachable geothermal resources, as well as Italy and Turkey.
No wonder then that a lot of effort in geothermal has focused on the technology to make deeper drilling economical. It’s been a boon for the industry that Big Oil has joined the party. After all, these are the companies whose entry into geothermal makes the most sense, given they know drilling best.
Speaking about oil, some companies have been researching and testing something that could expand geothermal’s reach and benefit oil companies: turning abandoned oil wells into geothermal wells.
There are a few companies working in this direction, either turning abandoned wells into geothermal ones or making them double-use wells that yield both heat and oil. Theoretically, the transformation of oil wells into geothermal wells can be of great help for boosting geothermal’s popularity. Practically, however, it’s not that straightforward.
For starters, flow rates from such wells are much lower than from newly drilled geothermal wells, Jamie Beard from the Geothermal Entrepreneurship Organization at the University of Texas at Austin told Oilprice. Then there is the issue of heat: most oil wells are simply not hot enough to make economic sense if we are talking about electricity generation. Thirdly, Beard says, “existing wells often suffer from well integrity issues that will make them ill-suited for a 20-40 year lifespan as a producing geothermal asset.”
The good news is this does not mean turning abandoned wells into heat-producing reservoirs is completely off the table. Remember, electricity generation is the main purpose of geothermal drilling but heating should not be underestimated as an area of application, either.
Some companies are using abandoned wells to inject water into them, heat it, and use it for, well, heating. Power generation is also not out of the question if the well is right. Yet it seems that abandoned wells are better suited for heating purposes.
Even in that area, however, there are challenges, says Paul Stockley, head of Oil and Gas at UK-based law firm Fieldfisher. One of these is how long the water needs to stay in the well to become hot enough to be used for heating. The longer the time, the lower the viability of the system. Costs should also be borne in mind, Stockley notes. Even if drilling costs are taken out of the equation, there is injection equipment and transfer-of-heat equipment to consider.
It appears that abandoned wells are most viable as a heating source for nearby buildings and installations. For instance, Fieldfisher’s Stockley notes agricultural operations that can be heated. Since in the UK most onshore oil wells are near farmland, the match is almost perfect.
Not all abandoned oil wells, then, are suitable for converting into geothermal reservoirs. Some may, however, get a second life to heat up water that could then be used to heat a nearby facility. For electricity generation, new drilling appears to be the better option for the time being, overall. And, as with any other technology, costs are bound to continue falling, especially with the help of Big Oil investment. There are even new areas of research into harnessing the geothermal resources of the planet: flooding abandoned coal mines and using the water heated in this way to generate electricity and use it for heating and cooling.