Oil and gas companies have earned a bad reputation through their drilling practices, yet their advances in drilling technology that have made possible the extraction of oil and gas from super-deep wells have also been highly beneficial to the exploitation of renewable resources, and more specifically geothermal energy.
Currently, the USA leads the world in geothermal energy production, followed by the Philippines and Indonesia, with a projected worldwide geothermal energy production of over 100 TWh by 2020 according to the IEA.
Figure 1: Top 10 Countries - installed capacity
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Figure 2: Geothermal Generation and projection by region
Steam-producing geothermal wells are located in regions with active or geologically young volcanoes, which have the highest underground temperatures. Such “hot spots” occur at tectonic plate boundaries or where the thin crust allows heat to flow through. Attractive reservoirs typically have temperatures from 160 to above 300 degrees Celsius.
The high temperature environment and the highly fractured rock in these regions make drilling and completion very complex, most notably in the selection of tubular, downhole tools, and cementing materials. Geothermal drilling is still a small fraction of the activity of oil and gas companies, so much of the possible developments in advanced drilling and completion technologies for geothermal applications remain only a potential.
Unlike other forms of renewable energy (e.g. solar and wind) that are affected by the weather and produce variable power, geothermal energy distinguishes itself by providing base-load energy generation with a low carbon footprint. In a nutshell, geothermal plants use steam produced through wells drilled into hot reservoirs to drive turbines which generate electricity. Power plants are located in close proximity to such reservoirs and are divided into three types: Dry Steam, Flash Steam, and Binary Steam. Related: The Biggest Threat To Oil Prices Is The Dollar, Not A Supply Glut
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Figure 3: Dry Steam, Flash Steam, Binary Cycle Power plant.
Source: U.S. Department of Energy
Dry steam plants are the oldest and simplest form of geothermal plants where produced steam is directed to drive a turbine and condensed water is re-injected into the reservoir through an injector well. Flash steam plants are the most common, operating with water at temperatures above 182 C, which flows upwards from the reservoir and is converted to steam due to pressure and temperature changes. This steam is used to drive the turbine to produce electricity, while leftover water and condensed steam is re-injected into the well. Binary cycle plants operate at lower temperatures between 107 C – 182 C. Hot reservoir water is used to evaporate a secondary fluid through a heat exchanger which drives a generator to produce electricity in a closed circuit.
Unconventional Geothermal Resources (UGR) has been of interest in recent years, although the idea of using geothermal energy to produce power is not new. The first Dry Steam plant was built in 1904 in Larderello, Tuscany, Italy and is now the site for the DESCRAMBLE (Drilling in dEep, Super-CRitical AMBient of continentaL Europe) project. Coordinated by ENEL Green Power of Italy, this fascinating project is based on the theory that a super-critical geothermal well can produce over 10 times the power that a conventional geothermal well generates. The ultimate purpose of the project is the chemical and thermo-physical characterization of a deep steam reservoir through increasing the depth of the well Venelle 2 from 2.2 km to 3.5 km.
If successful, the project will proceed to Phase 2, which is the creation of a pilot power plant. The success of this project and would significantly increase capacity through less wells required per MWe of production and makes geothermal energy more attractive as drilling represents about 30-50 percent of the costs associated with a geothermal project. The project initiated in May 2015 will last 3 years and is on the verge of a major technological breakthrough to produce “super-critical” water. At temperatures above 374 C and pressures above 218 bar, water reaches super-critical conditions and exists in a physical form incorporating both liquid and gas phases. Related: Poland Resists Global Shift Away From Coal
Super-critical water behaves like a powerful acid and can be detrimental to drilling electronics and equipment, which is what makes drilling so challenging. Logging tools for such harsh environments are currently under development at Norwegian research company SINTEF. With extensive experience with instrumentation in the oil and gas industry, SINTEF is pushing the boundaries to develop logging tools that can withstand temperatures exceeding 300 C down-hole.
Logging tools represent just one of the many challenges encountered; further research is to be conducted in managing the corrosive effects of completion fluids, equipment and cementing. One other deep-drilling project DDP-1 was initiated in Iceland aiming to drill to 4km, but unfortunately geologists encountered lava at a depth as shallow as 2 km with temperatures exceeding 450 C and the project was later shut down.
The approach of exploiting geothermal energy is very similar to that employed by oil and gas companies, which have been drilling wells of depths greater than 10 km. Such geothermal projects represent an opportunity for oil and gas companies to advance in technological development and diversify their revenue sources.
By Qarnain Foda for Oilprice.com
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