The potential contribution of geothermal energy to ...

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International Journal of Sustainable Energy, 2014 http://dx.doi.org/10.1080/14786451.2014.950966

The potential contribution of geothermal energy to electricity supply in Saudi Arabia D. Chandrasekharama,b∗ , Aref Lashinc,d and Nassir Al Arifia a Geology

and Geophysics Department, College of Science, King Saud University, PO Box 2455, Riyadh 11451, Saudi Arabia; b Department of Earth Sciences, Indian Institute of Technology Bombay, Mumbai 400076, India; c Petroleum and Natural Gas Engineering Department, College of Engineering, King Saud University, PO Box 800, Riyadh 11421, Saudi Arabia; d Geology Department, Faculty of Science, Benha University, PO Box 13518, Benha, Egypt (Received 29 May 2014; accepted 23 July 2014) With increase in demand for electricity at 7.5% per year, the major concern of Saudi Arabia is the amount of CO2 being emitted. The country has the potential of generating 200 × 106 kWh from hydrothermal sources and 120 × 106 terawatt hour from Enhanced Geothermal System (EGS) sources. In addition to electricity generation and desalination, the country has substantial source for direct application such as space cooling and heating, a sector that consumes 80% of the electricity generated from fossil fuels. Geothermal energy can offset easily 17 million kWh of electricity that is being used for desalination. At least a part of 181,000 Gg of CO2 emitted by conventional space cooling units can also be mitigated through ground-source heat pump technology immediately. Future development of EGS sources together with the wet geothermal systems will make the country stronger in terms of oil reserves saved and increase in exports. Keywords: geothermal energy; EGS; carbon dioxide; CDM; ground-source heat pump

1.

Introduction

Saudi Arabia is the world’s largest producer and exporter of oil and gas in 2012. It has the world’s second largest crude oil reserves and is also the largest crude oil producer in the world, the first being Russia. Almost 90% of the country’s export is oil and oil-related products and these two are the main source of revenue to the country (OPEC 2012). As on date, Saudi Arabia’s exploration and production (E&P) company, ARAMCO, the state-owned oil company, has reached its production target of 12 million barrels per day. The country, at present, is focusing on natural gas production, refineries and electric power industries. Saudi Arabia is the world’s 13th largest consumer of total primary energy. About 60% of electricity is generated by oil and the remaining is generated by gas. In recent years, ARAMCO has realised the importance of renewable energy, and cautioned that the country will be losing revenue on three million barrels per day of oil export by the end of the decade if no effort is made to reduce dependence on oil by domestic users. The country in deed has considerable wet and Enhanced Geothermal System (EGS) resources yet to be exploited. By adopting the policy of energy source mix using geothermal ∗ Corresponding

author. Email: [email protected]

c 2014 Taylor & Francis

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D. Chandrasekharam et al.

and other renewables, the country can reduce dependence on fossil fuel for part of its energy demand and the renewable sources may help the country to retain its supremacy over the world with respect to oil and gas exploration and exports, and also extend the life of oil reservoirs for a longer period than that estimated now (Alnatheer 2005).


2.

Current electricity generation

The Saudi Electric Company is the largest electricity provider followed by the Saline Water Conversion Corporation. A small percentage is produced by independent power producers. ARAMCO is planning diversification into the business of electricity generation to meet the growing demand and to increase the electricity generation capacity from the present 240 terawatt hours to 736 terawatt hours by 2020 (IEA 2012, 2013). A part of this will be from solar and nuclear sources (EIA 2013). At present the entire electricity is being generated from oil and gas. Diversification of energy sources to increase the export of oil by another three billion barrels is being planned to increase the export to 10.5 million barrels per day from the current export of 7.5 million barrels per day. Saudi Arabia’s estimated population of 27 million (IEA 2012) is spread over an area of 2.2 million km2 , and the country’s electricity production has increased from 126 terawatt hours in 2000 to 240 terawatt hours at present with present per capita energy consumption of 8500 kWh (IEA 2012, 2013a). The demand for electricity is growing at the rate of 7.5%/year. According to a recent estimate, 240 terawatt hours of electricity was consumed in 2010 from oil and gas and the projections are that the country’s generation capacity will reach 736 terawatt hours by 2020 (IEA 2012; WB 2009) by burning 500,000 barrels of oil. In summer season this number will reach 900,000 barrels. Building sector is a major consumer of electricity with 80% of the energy spent for space cooling. According to the recent report by IEA (2013a), Saudi Arabia has greater than 3000 cooling degree days which is the highest among other countries of similar population. Beside power and buildings, 17 million kWh is needed for desalination plants to provide 235 L/day per capita of drinking water. The per capita electricity consumption by the country is expected to grow to 10,000 kWh by 2020 from the current 8500 kWh (Figure 1, WB 2009). By using fossil fuel for meeting the ever-growing electricity demand, the country is generating considerable volume of CO2 . Implementing clean development mechanism (CDM) through renewable energy resources (Al-Saleh, Upham, and Malik 2008) such as geothermal energy will not only reduce CO2 emission but also bring considerable power and revenue to the country.

3.

Present status of carbon dioxide emission

The country’s CO2 emission from fuel combustion has increased from 252,000 Gg in 2000 to 446,000 Gg at present, with oil contributing 175,000 Gg and gas contributing 77,000 Gg (IEA 2012). The emission by different sectors is shown in Table 1. The current per capita emission of CO2 has increased to 0.016 Gg from 0.012 Gg in 2000. With constant increase in per capita electricity consumption (Figure 1), the CO2 emission will only increase in future. This trend is not a healthy sign for the country. CO2 emission is detrimental to the environment and causes concern on global climate change and sea level rise (IPCC 2007). Since Saudi Arabia experiences extreme climate variation in a year, excess emission of CO2 will influence the local weather pattern, which is being experienced by several countries. In fact Saudi Arabia is already experiencing change in the weather pattern and the ambient temperature over the past decade has increased by 0.70◦ C (Almazroui et al. 2012). Like other urbanised countries,


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Figure 1.

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Annual Electricity consumption of Saudi Arabia.

Table 1.

CO2 emission by different sectors of Saudi Arabia (Gg).

Total CO2 emission Electricity and heat Manufacturing industries from fuel combustion production and construction Transport 4,446,000

181,000

161,000

104,000

Saudi Arabia spends 80% of its electricity for space cooling purpose (IEA 2013b). Although carbon capture and storage technology is being advocated by several countries (Rahman and Khondaker 2012), the technology is not yet matured.

4.

Geothermal resources potential of Saudi Arabia

Saudi Arabia has not undertaken any systematic investigation on its geothermal provinces. Due to concerns related to global warming and environmental issues related to emission of large volumes of greenhouse gases such as CO2 and methane (IPCC 2007), the country has now taken initiative to promote renewable energy resources to reduce dependency on fossil fuels and to increase its GDP by exporting the domestic consumption of three billion barrels of oil. This initiative is an essential step towards a healthy and sustained energy security development and to cultivate CDM by reducing CO2 emission. There are two geothermal systems in Saudi Arabia that are confined to the western part of the shield region: wet and hot dry rock geothermal systems controlled by volcanoes (known as Harrats) and high heat generating granites respectively (Figure 2). Further the country, in general, has sufficient underground heat to support direct applications such as space heating/cooling, greenhouse cultivation, refrigeration and dehydration (Al-Dayel 1988; Rehman and Shash 2005; Rehman 2010; Al-Rashed and Asif 2012; Lashin and Al-Arifi 2012; Hussein et al. 2013).


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Figure 2. Geology of the western Arabian shield. Notes: M, Midyan terrane; H, Hijaz terrane; J, Jeddah terrane; A, Asir terrane; Af, Asif terrane. Percentage of granitic and intermediate rocks outcropping in these terranes is given in Table 3. Source: Adapted from Elliott (1983) and Stoeser (1986).

4.1.

Evolution of the hydrothermal systems

The genesis of the hydrothermal systems is coeval with the geological and tectonic evolution of the Nubian and Arabian plates and the opening of the Red Sea. The break-up of these plates was initiated by the Afar plume that covered a large region in Africa and Arabia. According to seismic tomographic investigation (Debayle, Leveque, and Cara 2001), a large plume head was located below Ethiopia and the periphery of the plume extended below the southern part of Saudi Arabia, Djibouti and Yemen before the initiation of the Red Sea rift (Figure 3). The initial volcanism over the Arabian shield was the result of this plume activity that gave rise to the volcanic centres (known as Harrats) at Harrat Uwaynd, Harrat Hadan and Harrat Sirat (Figure 4). Yemen also experienced major volcanism during this stage that gave rise to a large number of fumaroles, thermal springs and gas vents (Minissale et al. 2007, 2013). The initial plume and volcanic activity propelled the Red Sea rift that started from the southern part and propagated northwards. This process occurred between 31 and 5 Ma. As a consequence of this rift propagation, the western coast of the shield experienced regional dike swarm activity parallel to the Red Sea rift axis (Bayer et al. 1989; Camp and Roobol 1992; Bosworth, Huchon, and McClay 2005) and this activity still continues at the present, as evident from the recent


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Figure 3. Location of the plume head that divided the Nubian and Arabian shield regions. Source: Adapted from Bosworth, Huchon, and McClay (2005).

Figure 4. Evolution of the Harrats and tectonic features along the eastern margin of the Red Sea. Source: Adapted from Bosworth, Huchon, and McClay (2005).

earthquake swarm below Harrat Lunayyir (Figure 2) (Al-Shanti and Mitchell 1976; Pallister et al. 2010; Duncan and Al-Amri 2013). Post-rift tectonic activity resulted in the eruption of large volumes of volcanic flows and these volcanic centres or the younger Harrats are located at Uwaynd, Khaybar, Rahat, Kishb, Nawassif and Al Birk. The area occupied by the volcanic flows is 90,000 km2 (Coleman, Gregory, and Brown 1983). These volcanic flows have covered a large part of the paleo-channels along the west coast giving rise to hot aquifers below the volcanic centres. The steam from these aquifers and the steam separated from the basaltic magma have given rise to fumaroles around several Harrats. The geothermal gradient recorded in these areas is 90◦ C/km (Coleman, Gregory, and Brown 1983). During the Red Sea rifting and spreading activity Eritrea, Djibouti, Ethiopia, Yemen and Kenya experienced similar volcanism with the eruption of large volume of flows. Thus, the volcanic and tectonic activity over the land masses (Eritrea, Djibouti, Ethiopia, Yemen and Kenya) surrounding the Red Sea is coeval, and hence the

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Table 2.

Chemical composition of representative thermal springs from Al-Lith and Jizan.

Sample No Tem ◦ C pH Location

Na+

K+

1 2 3 4 5 6 7

510 424 533 473 852 900 1025

19.5 12.5 40.3 23.6 27 30 28

76 79 61 76 75 59 55

7.3 7.7 7.6 7.4 7.1 7.3 7.7

Al Lith Al Lith Al Lith Al Lith Jizan Jizan Jizan

Ca++ Mg++ 201 234 341 429 252 549 433

4 0.1 15 60 14 56.2 32

Cl− 597 687 941 586 671 1934 1492

HCO− SO− 3 4 74 21 20 16 142 216 200

700 440 215 238 402 470 330

Source: Modified from IEA (2012). Data on samples 5–7 are from Hussein and Loni (2011).

associated geothermal systems in these countries. Kenya is generating 500 MWe from Olkaria geothermal field and Ethiopia’s Tendaho will soon be generating 5 MWe from its pilot geothermal power plant. Based on extensive field and power production assessment, number of geothermal wells drilled in the volcanic flows, Bodvarsson et al. (1987) estimated average power production capacity of the volcanic fields. The power production capacity of 1 km2 volcanic flows under similar tectonic settings is about 173 × 106 kWh (Bodvarsson et al. 1987). In the case of Saudi Arabia, assuming that about 10% energy is extractable, the Harrats, which occupy about 90,000 km2 , should be able to generate 200 × 106 kWh of electric power (Chandarasekharam, Lashin, and Al Arifi 2014a, 2014b). There are also hydrothermal systems associated with granites, such as those occurring at AlLith and Jizan (Figure 2). The chemical composition of the thermal waters occurring in the granites is shown in Table 2. The thermal springs from both the sites show chloride enrichment (597–1934 ppm, Table 2) even though there is no indication of Red Sea involvement with these springs. Fluids circulating in granites for a long period of time incorporate large amount of chlorine from chlorine-bearing minerals such as mica, hornblende and apatites, thus recording higher chloride content. The granites that host these springs do contain such minerals (Wier and Hadley 1975; Hadley and Fleck 1979; Elliott 1983; Harris 1985; Pallister 1986a, 1986b). Granite–water interaction experiments at elevated temperatures gave high chloride content in the reacted water (Savage et al. 1985; Chandarasekharam and Antu 1995). The low tritium values in the thermal waters suggest long circulation time within the granite reservoir, thus allowing the water to react with the minerals mentioned earlier for a long period of time (Chandarasekharam, Lashin, and Al Arifi 2014a, 2014b; Lashin et al. 2014). As discussed in section 4.2, these granites, hosting the geothermal systems, are high heat generating granites (11 µW/m3 , Mooney et al. 1985; Gettings et al. 1986) due to high content of uranium, thorium and potassium. In addition to the inherent heat generated by the reservoir rocks, this area falls, as shown in Figure 1, above the mantle plume periphery. The reported heat flow value in this region is about >80 mW/m2 , which is nearly twice the average global heat flow value (∼45–50 mW/m2 , Rybach 1976). 4.2.

Evolution of EGS

The western Arabian shield, during its initial stages, evolved as microplates, the junctions of which are represented by ophiolite zones. The most prominent microplates, known as terranes, are shown in Figure 2. These terranes also represent the location of paleo-suture zones related to arc tectonics (Stoeser et al. 1984; Stoeser 1986). These paleotectonic features are overprinted by later (