Gas Injection

Schlumberger came to us with another phenomenon to simualtion: the injection of gas in order to optimize oil recovery.

Indeed, oil extraction can be devided into different recovery stage. During the primary recovery stage, which corresponds to the first years of production, reservoir drive comes from a number of natural mechanisms: underground pressure in the oil reservoir is sufficient to force oil to the surface. However, over the lifetime of the well, pressure fall and is insufficient to force oil to the surface.

Therefore, after natural reservoir drive diminishes, secondary recovery methods are applied in order to increase reservoir pressure and thereby stimulate production.

Water or gas injection is a secondary recovery method used by oil and gas companies to increase oil recovery from an existing reservoir. Water or gas is injected to support pressure of the reservoir (also known as voidage replacement), and to sweep or displace oil from the reservoir, and push it towards a well.

Normally only 30% of the oil in a reservoir can be extracted, but this method increases that percentage (known as the recovery factor) and maintains the production rate of a reservoir over a longer period.

In the Tarim Basin, due to the complex geometry of the karst reservoir, a large amount of oil is wedged into the cap of the cavities:  38,000 m3 of oil produced (32%) for 80,000 m3 remaining (68%).

               

                                          Oil wedged into the cap of the cavities

‚ÄčThe solution proposed by Schlumberger is to inject nitrogen, lighter than oil, in the reservoir to replace oil wedged  in the cavities. 

In this BEI, CFD simulations are therefore carried out in order to simulate this phenomenon. These CFD simulations will than help Sclumberger to understand flow behaviour in a case of gas injection and see how the technique can be optimized. Moreover, a comparison of CFD simulation and automata simulator results will permit to validate the reservoir simulator developped by Schlumberger for a three-phase flow.