A new player -at least in the United States- is entering in the game with a lot of enthusiasm among some of the audience, and a lot of skepticism by some others, that this unconventional player will overtake the conventional ones any time soon. Although, Big hops are held on the new player in the future.
This new player is oil shale. The number estimated of oil shale in place in the US is around 4.28 trillion Barrel. An immense amount that’s even hard to imagine. Unfortunately, this amount is not 100% recoverable and the actual recoverable amount is unknown due to the lack of economic methods of recovery. The extraction of economic quantities of oil shale will be true in the near future due to the huge investments in this field.
Shale oil can be extracted by pyrolysis, electrofracking, and rubbulization of oil shale. Oil shale lies between crude oil and coal in both of its appearance and composition. It is a carbonate rock that contains a significant amount of Kerogen. Kerogen is an intermediate stage that hydrocarbons pass through in the process of changing from organic materials to crude oil and gas. Several technologies are proposed for extracting shale and pyrolysis is one of them. Pyrolysis is a thermochemical decomposition of organic material at elevated temperature in the absence of oxygen. This process causes a change in the chemical composition and the phase of the hydrocarbon present in the Kerogen.
Pyrolysis of rocks can be performed either above ground or within the rock formation itself. Most oil shale industries perform the shale oil extraction process after the rock is mined, crushed, and transported to a retorting facility. The temperature at which Kerogen decomposes into usable hydrocarbons varies with the time scale of the process; in the above-ground retorting process decomposition begins at 300 °C (570 °F), but proceeds more rapidly and completely at higher temperatures.
Decomposition takes place most quickly at a temperature between 480 and 520 °C (900 and 970 °F). On the other hand, there are several experimental technologies of performing the process in place (in-situ). Shell Oil is working its In-Situ conversion process by which electrical heaters will be placed in vertical holes covering the whole thickness of oil shale sections. 15 to 25 holes per acre will have heaters evenly heating the rock from two to three years allowing hydrocarbon to escape out of the Kerogen. Then, liquid oil is recovered.
Besides pyrolysis, electrofracing is another technique for extracting oil shale. Fracking in general is simply pumping special fluids, called frac fluid, down wells under high pressure and pumping rates in order to fracture (crack) a desired rock formation. This will create wider paths for hydrocarbon (oil and gas) to come through. In other words, it’s a mean of increasing hydrocarbon production. For the purpose of enhancing shale oil production, hydraulic fracturing is applied to horizontal wells. These are wells that penetrate the shale oil layer horizontally. These wells will be fractured and treated with proppant.
Proppant is a special frac fluid additive. It will keep the induced fracture open during and after treatment simply by filling it. Proppant is made of wide variety of material such as ceramics and glasses, but for electrofracking purpose it has to be electrically conductive. ExxonMobil is still developing this technique; it uses a series of hydraulic fractures created in the oil shale formation. These fractures should be longitudinal vertical fractures created in the horizontal zone of wells and conducting electricity across each well. Electrically conductive proppant will form the heating elements across the fractures when electrical current is applied.
These wells are called heating wells, they are placed in a parallel row with another horizontal well intersecting them at their bottoms. This allows opposing electrical charges to be applied at either end. Laboratory experiments have demonstrated that hydrocarbons are expelled from heated oil shale even under in situ stress. Electricity generators or simply heaters can be placed on surface or in the well bore. Surface heaters are better for maintenance issues. The heated shale oil is then extracted by separate dedicated production wells. After pyrolysis and electrofracking, comes rubbulization the third approach to the economic recovery of shale oil.
This approach was taken by Chevron Oil Company. Rubbulization is breaking a zone of reservoir into separate chunks of rock .In other words, generating fractures in the three dimensions. while heated carbon dioxide is used for the decomposition Kerogen in oil shale. The process involves drilling vertical wells into the oil shale formation and applying horizontal fractures induced by injecting carbon dioxide through drilled wells and then pressured through the formation for circulation through the fractured intervals to rubbulize the production zone. Rubbulization propellants and explosives may be used. The used carbon dioxide then is routed to the gas generator to be reheated and recycled.
The remaining organic matter in previously heated and depleted zones is combusted in-situ to generate the heated gases required to process successive intervals of treated wells. These gases would then be pressured from the depleted zone into the newly fractured portion of the formation and the process would be repeated. After that, the hydrocarbon fluids are brought up in conventional vertical oil wells as any other conventional well. The new unconventional energy source is not new itself. What‘s new is considering it as another economical energy source rather than an alternative to conventional sources.
And this became true only in the last 10 years because of the oil price boom. Experts say that oil shale industry will continue progressing at a fast paste as long as oil price is above the $95 threshold. Shale oil can be extracted from shale formations economically using one of the following processes; pyrolysis, electrofracking, or rubbulization. Even though the technical and scientific basis for commercial recovery of shale oil is almost complete, number of factors need to be aligned for that to become true. These factors include infrastructure, byproduct treatment facilities and most importantly trained work force.