HOW SOLVENT GAS CAN BE USED TO BOOST OIL PRODUCTION

One EOR technique PDO is implementing is miscible (as opposed to immiscible) gas injection. The technique consists in injecting a gas into the reservoir into which the oil can dissolve. The resulting gas/oil solution can move more easily through the reservoir rock, and up and out the producing wells.

However, a gas will dissolve in oil only under certain conditions of temperature and pressure and only if it has the right chemical composition. Moreover, for this recovery method to work economically there must also be an efficient system to recover the oil-in-gas fluid. In other words, the injection and production wells must be put in exactly the right spots for maximum recovery. So it’s no surprise that, before any miscible gas flood can be undertaken, a great deal of information has to be gleaned from the reservoir and analysed in detail. First, samples of the oil in the reservoir are tested to find out the composition and temperature/pressure combination that will encourage optimum miscibility.

An aerial view of a typical gas injection facility

The other key task is to ensure that the injection wells are ’connected’ with the producer well, i.e., that the oil displaced with the miscible gas can reach a well that will bring it to the surface.

The final key task is studying the reservoir structure and its rock and fluid properties and developing a computer model that shows how the miscible gas flood will work under various scenarios.

As with other EOR techniques, miscible gas injection is both difficult and expensive, and it can only be used when the economics justify it. Safety issues are also paramount. When gases (some of them toxic) are being injected at around 500 times atmospheric pressure, the surface facilities have to be extremely robust. And they have to boast a whole range of fail-safe mechanisms to ensure that nothing goes wrong.