The process of producing oil from evaporite rocks is complicated and involves a series of steps and experiments. According to Cater (2002) the best way to obtain oil and gas is to drill down at the depths of 1,000 to 5,000 m below the surface where evaporite rocks are found. Cater (2002) continues to say that “the primary consideration when drilling the rock should be to keep the drill bit lubricated and turning and also to maintain enough pressure in the hole to contain any of oil or gas encountered” (51). He continues to say that as the drill drives down into the hole, a stream of mud seeded with dense materials to increase its weight and is circulated by a pump (Cater 2002).
Cater established that caving in of the wellbore is particularly common in mudstones which swell and flake off as the drilling mud washes over them (2002). Cater (2002) also stated that some rock salt and other evaporite rocks may dissolve as they are drilled. The process of extracting oil from evaporites goes through some stages which include firstly identification of the evaporites (Nely, 1994). Secondly according to Nely (1994) the process involves drilling rate which varies markedly according to the evaporite sequence. There are variations in the drilling rate which can be minimized through some conditions of drilling for example drilling with light weight tools, turboring with a diamond bit and using high density oil mud.
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The next step involves studying the extracts to establish if the mud is oil saturated or contains saturations of salt water. After it has been established that the evaporites contain compositions of oil Nely (1994) stated that “the cuttings may be washed with detergents, sodium carbonate, gas oil or chloroform according to the techniques used by the technical committee of that company” (p. 2). In other occasions emulsifier or emulsifying agent can be used. According to Hyne (1991) “lignosulfonate and surfactants are used as emulsifiers in drilling mud. Produced fluids can be oil in water in which droplets of oil can be suspended in water and less commonly, water in oil in which droplets of water are suspended in oil” (p.168). Hyne (1991) continued to say that “the produced emulsions are commonly treated with heat, electrostatics and other chemicals to separate them” (p. 168). The final product is usually the accumulation of basic sediment and water on the bottom of the tanks. This can be demonstrated in the figure 4.0 shown below.
Some of the problems that may be encountered during the drilling process is that water entry can take place while drilling even in the middle of and evaporite sequence. Nely (1994) continues to say that “because evaporites constitute an impermeable cover, this can hinder the normal expulsion of interstitial waters contained in the underlying sediments” (p.8). He therefore says that this can give rise to abnormal high pressures and temperatures which can hinder the drilling process. Cater (2002) says that sampling of rocks at depth is expensive which is another difficult that can be encountered. Remote sensing techniques are also available nowadays which are also very expensive (Cater, 2002).