This article will examine the salt dome formation, classification of fractures, hydrocarbon contribution, and the importance of locating fractures to prevent sudden subsidence to cities of the Dammam Dome using Lineament.Introduction
Rock fractures are widely spread within an area underlain by carbonate rocks in the Eastern Province of Saudi Arabia, namely the Dammam Dome. Fractures are important to create hydrocarbon reservoirs. However, they might also affect urban planning in cities, including Al-Khobar, Dhahran, and Dammam by creating cavities, and subsidence.
The outcome of this paper is to highlight the formation of the Dammam salt dome, classification, importance of fractures in hydrocarbon reservoirs, and to avoid land subsidence using Lineament.1. Salt Dome Formation
The Dammam Dome is a column of salt rises to the surface creating a salt dome. Two properties of rock salt that contribute to form the dome. First, when the salt is buried deeper than 300 [m], its density will become less than the surrounding rocks. Second, the pressure of the overlying rocks above the salt gives the ability for the salt to deform, and flow like viscous fluids (King, n.d). Consequently, the resulting structure will be a dome accompanied with intense fractures that will be classified in the next section (Hariri, 2006, p 5).2. Classification
Fractures within Dammam Dome can be classified into two features. First, based on size, trend, and extension:
1. Major fracture
2. Minor fracture
3. Very small fracture
Second, based on principal stress3:
1. Mode I fracture
2. Mode II fracture
3. Mode III fracture (Hariri, 2006, p 5). 2.1. Based on Size, Trend, and Extension
There are three types of fractures in this feature. Examples bring in, major fractures are characterized by their large size, and long extension that can be extended to 1 [km] (Hariri, 2006, p 5). Furthermore, minor fractures are characterized by their short extension to 55 [m] on average, and small size. In addition, very small fractures are characterized by their very small extension 1 [m], and their very small size (Hariri, 2006, pp 6-7).2.2. Based on Principal Stress
Fractures resulting from principal stress vary from each other. In mode I (opening), sigma 1 is perpendicular to the plane of crack. Whereas, in mode II (Shear fracture), the fracture surface is oblique to sigma 1 with an angle theta of 30 degrees to 45 degrees. Mode III (Shear fracture), sigma 1 is parallel to the fracture plane. Oblique extensional fracture is a combination of mode I, II, and III creating a sliding motion that is found to be parallel, and in the same time, perpendicular to the fracture surface (Hariri, 2006, pp 4-5).
Further, fracture propagation are controlled by the fracture tip of the stress field that is perpendicular to sigma 3. What is more, as fracture volume decreases, the pore pressure will decrease as well, and fracture propagation will arrest (Hariri, 2006, pp 4-5). 3. Importance
Dammam Dome fractures are important to the petroleum industry, and urban planning.3.1. Oil, and Gas Reservoirs
Fractures serves an important role to the petroleum industry. In this case, extensional tectonic forces create weak zones for the low density salt to exploit, as discussed previously in the Salt Dome section. As the salt continues to grow, it arches the cap rock above it allowing oil, and natural gas to migrate, and accumulate in the structural dome trap (King, n.d). 3.2. Subsidence
In addition to hydrocarbon reservoirs, locating major fractures within Dammam Dome in growing urbanized areas can help to prevent geo-hazard like subsidence. Lineament studies provide an aerial picture of possible fractures of weak zones that might be difficult to be noticed in the field. Moreover, by selecting different sun-angles, the aerial photos are improved (Hariri & Abdullatif, 2005, pp 4-6). Conclusion
In conclusion, Dammam Dome is dominated by intensive fractures, as a result of doming process that contributes in oil, and natural gas reservoirs. In the same token, it is important to locate these fractures using Lineament to avoid subsidence in growing industrial cities above the Dammam Dome, such as Al-Khobar, Dhahran, and Dammam.
Hariri, M. M. (2006). Nature, affects, and possible causes of rock fractures within Dammam, Khobar and Dhahran cities, eastern Saudi Arabia. Gulf First Planning and Development Conference 20-22 February 2006. Kuwait. Retrieved October 31, 2014, from http://faculty.kfupm.edu.sa/ES/mmhariri ... hahran.pdf
Hariri, M. M. & Abdullatif. O. (2005). Use of The GIS To Delineate Lineaments From Landsat Images, Dmmam Dome, Eastern Saudi Arabia. XXII International Cartographic Conference (ICC2005). A Coruna, Spain, 11-16 July 2005 Hosted by: International Catographic Association (ICA-ACI). Retrieved October 31, 2014, from http://faculty.kfupm.edu.sa/ES/mmhariri ... eamnts.pdf
King, H. (n.d). Salt Domes. Geology. Retrieved November 2, 2014, from http://geology.com/stories/13/salt-domes/