Zagros diapers, storage & section study

Category Tectonic & Seismotectonic
Group GSI.IR
Location 21th symposium on geosciences
Holding Date 24 May 2008

      Much of what is now known about past and present movements of Iranian salt diapirs has come from a research project being run jointly by geologists from the Department of Earth Sciences at UppsalaUniversity in Sweden (mainly professor C. J. Talbot) and the Institute for Earth Sciences at the Geological Survey of Iran. This project started as the Zagros Halokinesis project in 1994. Oil is currently the world's most important primary energy fuel and, on a global basis demand for oil should continue to grow at a moderate pace. Near and Middle Eastern countries hold two thirds of the world oil reserves and a significant proportion of these are in Iran. The price of oil is not constant and an efficient storage system of large capacity would allow Iran to smooth out short-term price fluctuations if not actually control the long-term price of oil. Such a storage system could be in caverns dissolved in some of the 250 emergent salt diapirs or in diapirs that are blind beneath the surface. Liquid gas (propane and butane) can replace oil for many uses and the storage of liquid gas is also likely to become important on its way its export to countries around Iran .The subsurface storage of liquid gas, oil and other fluids was developed long ago in the USA but it important to remember that several such storage caverns have failed. Storage is easier, cheaper and strategically safer in cavities dissolved in deep salt bodies than in any other engineered storage capacity. Salt diapirs and the structures in their associated country rocks therefore have great economic potential, not only as natural traps of crude hydrocarbons, but also for the artificial storage of refined hydrocarbon liquids or gasses. This is because it is comparatively inexpensive to dissolve large storage caverns at strategically safe depths in appropriate salt diapirs. Many of the salt diapirs of Iran are beside the Persian Gulf on the export route for oil or gas of the new countries to the North(exploration of oil in these countries need export and Iran with a Gulf is a best way for export and diapirs in Iran can use for short time price of oil). Other diapirs are reasonably close to major cities elsewhere in Iran and can be considered potential storage sites for crude oil, refined hydrocarbon liquids or gasses pumped from elsewhere. Many diapirs in Iran can be use for storage of the common oil fields in SW Iran (common between Iran and Iraq-). Diapirs of Central Iran (in Great Kavir) also can be use in future for storage of radioactive wastes or other wastes, because the Great Kavir diapirs are far from cities. Iran is unusual in that so many salt diapirs emerge at the surface. This not just because Iran is so dry, it is because the region has been so tectonically active for the last hundred million years. Iran is still tectonically active and a significant problem is that many salt diapirs of Iran are currently active and either growing toward the surface, already there, or reached the surface so long ago that their salt is being, or has been, dissolved. The search strategy for suitable diapirs in any one region is likely to start with a desk study of the diapirs and their settings to identify accessible well known diapirs of homogeneous pure salt that are tall with large diameters. Any existing gravimetry and seismography should be used at this stage to check positive signs of deep voluminous salt rather than secondary salt welds along diapiric stems that are empty. Pattern of salt diapirs in any one region can be analyzed to identify gaps under which diapirs might still be beneath the surface. Talbot et al. (1991) considered the patterns of salt diapirs rising through ductile overburdens and Koyi (1985) has discussed various relationships between diapir patterns and basement faults. Supplementary modern geophysics should be carried out at about the time field geologists are studying the composition and (past or present?) kinematics of the salt body -and supplies and drainage of nearby water or brines with acceptable cushion gas content. If the salt mass targeted is active (as is likely in most of Iran), its kinematics and budget should be determined over a number of years, because the movements can be change the dig of storage. Analysis of borehole logs and cores are advisable before cavities are designed with the use of analytical and numerical models. Ground topography should be surveyed before, during and after water-dissolution of cavities so as to monitor surface subsidence and check that it fits expectations modeled in advance. The flow rates of active diapirs are significant for storage, and the shapes of the mountains are potentially part the selection criteria of diapirs suitable for storage caverns. Young, post- shortening diapirs appear to be the most appropriate in the Zagros for the storage of oil or gas because they generally contain the most salt. However, some of them are also surprisingly active. The pattern of salt diapirs in the Zagros was analysed by Rogers (1980, unpublished MSc thesis, Dundee University, Scotland) who identify gaps under which diapirs might still be blind beneath the surface. Still-blind diapirs deflect the drainage pattern by doming first unconsolidated gravels and, after these have been eroded, their carbonate overburden. The emergent blind diapirs are very important for storage. Extrusive domes of salt are soon surrounded by a plateau of salt flowing in unconstrained directions over the surrounding scenery so that mature salt extrusions develop the profiles of viscous fountains (Talbot & Jarvis 1984, Talbot 1993 and 1998-Fig1). When the supply of diapiric salt to a salt fountain is exhausted or isolated from its deep source by thrusting, the fountainhead sinks into and thickens the surrounding salt plateau. No longer supplied from below, the extruded salt mass thereafter merely spreads with a volume slowly diminishing by erosion. Together with the profiles of namakiers supplied from out of section, profiles of such salt mountains fit the non-dimensional, mathematically-modeled profiles of viscous droplets (Huppert, 1982-Fig1). They tend to maintain these profiles even as they waste beneath cloaks of insoluble cap soils. Shape of the salt extrusions is very important for the selection of diapir for storage (Fig1). The burning of oil as an energy source is to squander its potential. If we do not understand the true potential of our oil (really black gold) we will waste it. Nevertheless, oil is now the world's most important primary energy fuel and, on a global basis, demand for oil should continue to grow at a moderate pace. A lack of discipline among certain oil producers in the Middle-East, combined with a lack of strong exploration technologies suggested that our oil reserves "must be protect some of it for future peoples.

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