Oil shale represent a huge potential hydrocarbon energy source. The conventional methodologies used so far for exploiting this resource has very low economics and big environmental impacts. The possibility to obtain valuable products by directly upgrading the shales in-situ might be a breakthrough. In this study two cases were analyzed in order to give a first insight into this new technology. In particular it was evaluated the energy ratio between the calorific content of the produced fluids and the electrical heating supplied.
The slightly positive ratio suggests that more carefully evaluation and further research are required before any commercial development might be considered.
Oil shales are sedimentary rocks containing a high proportion of organic matter (kerogen), which can be converted into a material similar to petroleum by heating.
Great quantities of oil shale are available worldwide: 1.6 trillion barrels of oil are contained in oil shales around the world, according to the US Office of Naval Petroleum and Oil Shale Reserves estimation: the amount of oil obtainable from this source is comparable to the reserves of conventional oil. For this reason there is a big interest worldwide in technologies aimed at employing oil shales.
The technology currently employed in various country, like Estonia, Russia, Brazil and China, consists in mining the ores and burn them directly in power plants adequately equipped. An other possibility is to convert the kerogen into oil through pyrolysis: the oil shale is heated up to 450–500 ° C in absence of air. This process produces gases and light liquids together with a heavy carbon residue. This can be performed in surface plants, were the mined shales are pyrolysed. Recently a new approach consisting in heating oil shales directly in situ and producing gases and light liquids through wells has been proposed.
To evaluate the viability of the new approach two cases were considered; one from a publicly available field test on oil shales of the Green River area (patent WO 2001/81239) and another based upon lab analyses of an Italian source rock, relatively rich in kerogen (Castelli, et al.).
The field test was performed by heating in-situ oil shales at a depth of 30 m by electrical resistances (net pay of 17 m).
Based upon the well development description of the patent (6 heating wells and 1 producing well at a distance of 2.4 m, i.e. eight feet spacing), the temperature profile was calculated by employing a commercial CFD code (Fluent 6.2). In Figure the temperature at the producing well is presented.
The temperature calculated agreed with the production history reported in the patent: production started after nearly 100 days when the temperature reached 300 °C.
From the data reported it resulted that the ratio between the total calorific content of the gases and liquids produced and the given heating energy (energy ratio) was roughly 1.5.
Considering that this calculation does not take into account the efficiency to produce electrical power, this result is far from being satisfactory.
