Geothermal energy, a renewable energy source, comes from the Earth’s internal heat and results from geological processes like subsidence in sedimentary basins. As sedimentary layers bury, temperature and time increase, driving the thermal maturation of organic matter and leading to hydrocarbon formation. Heat flow from the Earth’s crust controls this process, influencing both hydrocarbon generation and geothermal energy potential.
Geothermal energy utilizations:
Geothermal energy users have directly utilized it for centuries, making it one of the oldest, most versatile, and most common forms of energy use (Dickson and Fanelli, 2003). Researchers have documented the early history of geothermal direct use in over 25 countries. Cataldi et al. (1999) reported that people have used geothermal energy for over 2,000 years.
Today, 78 countries directly utilize geothermal energy, a significant rise from the 72 reported in 2005, the 58 reported in 2000, and the 28 reported in 1995 (Lund et al., 2010).
Users consume 438,071 TJ/year (121,696 GWh/yr) of thermal energy, reflecting about a 60% increase over 2005 and growing at a compound rate of 9.9% annually. The distribution of thermal energy usage by category is approximately 49.0% for ground-source heat pumps and 24.9% for bathing and swimming (including balneology).
Space heating accounts for 14.4% of the total usage, with 85% allocated to district heating. Greenhouses and open ground heating consume 5.3%, while industrial process heating uses 2.7%. Aquaculture pond and raceway heating require 2.6%, agricultural drying takes up 0.4%, snow melting and cooling use 0.5%, and other applications account for 0.2% (Table 2). Egypt did not submit any data for WGC2005 or WGC2010. Lashin and Al Arifi (2010) also referenced a spa at Hammam Faraun.
Lund et al. (2005) estimated 1.0 MWt and 15 TJ/yr, and researchers assume these figures remain valid. Two main sources of geothermal energy exist for exploitation. Hydrothermal systems, first demonstrated in 1904, utilize naturally occurring hot water or steam trapped in or circulating through permeable rock to power steam-driven electricity generators.
More recently, since 1970, technology has been developed to extract the heat from hot rock by artificially circulating water through the rock to produce super-heated water or steam to drive the generators.
To generate electricity cost-efficiently, power plants require hot water and steam temperatures ranging from 120°C to 370°C. However, these naturally occurring hydrothermal resources exist only in a few regions where the Earth’s crust is very thin, typically along the edges of crustal tectonic plates. Over twenty countries have installed geothermal electricity-generating plants, and several more are planning new installations.
In shallow reservoirs or regions where water or steam temperatures range from 21°C to 149°C and remain too low for efficient electricity generation, communities use the hot water directly for local heating applications. The geothermal community widely considers Iceland a success story.
With a population of just over 300,000, the country now runs entirely on renewable energy. Geothermal energy supplies 17% of its electricity and 87% of its heating needs, while fossil fuels are still imported for fishing and transportation (Blodgett and Slack, 2009).
Effect of the geothermal energy on hydrocarbon maturation:
Thermal maturation occurs in progressively buried sedimentary layers as sedimentary basins subside. Organic, geochemical, mineralogical, and thermo-chronometric parameters indicate the thermal history.
Temperature and time primarily control the maturation of organic matter, while pressure plays a relatively minor role. This dependency on temperature and time explains how the reaction rate increases exponentially with temperature, influencing the rate of increase (Allen and Allen, 2006).
Sedimentary processes and heat flow primarily control the rate and extent of hydrocarbon maturation in potential source rocks, making them crucial in oilfield appraisal.
Organic matter-rich sediments generate hydrocarbons, which may migrate toward reservoir rocks if physicochemical conditions and timing align appropriately. Flow, transport, and reaction within sedimentary basins typically occur as slow and steady processes.
However, over the scale of geologic time, its effects are of great importance as they can generate important resources (Bitzer et al., 2001). The maturation of the hydrocarbons involves the slow thermodynamic conversion of the organic matter (Kerogens) in potential source rock into oil and gas, which may then migrate to more porous reservoir rocks.
Two factors heavily influence the maturation process: the local temperature and the duration of the thermal event. The rates of subsidence and sedimentation strongly control these factors.
During basin-forming events, the basement transfers large amounts of heat through the evolving sedimentary cover, which provides an energy source for the hydrocarbon maturation processes (Palumbo et al., 1999; Gray et al., 2012).
As in any ‘slow cooking’ process, however, maturation occurs at a given temperature only if the effective heating time is long enough. The maturation index, which depends on both the effective heating time and the thermal history, quantifies the degree of maturation.n. (Pieri 1988; Cranganu and Deming 1996).
