Ali, Hamza (Schlumberger) | Shah, Abdur Rahman (Schlumberger) | Akram, Agha Hassan (Schlumberger) | Khan, Waqar Ali (Schlumberger) | Siddiqui, Fareed Iqbal (Pakistan Petroleum Limited) | Waheed, Abdul (Pakistan Petroleum Limited) | Ahmed, Faizan (Pakistan Petroleum Limited)
A recent study addressed the modelling challenges of Alpha* gas condensate field. Alpha gas condensate field has a gas in-place of about 1 TCF, and both condensate and black oil production in addition. The field has been producing from two reservoirs SI and DI, for the past 26 years. Alpha field is subdivided into two segments called the Central Area and the Northern Area which are separated by a fault as shown in Figure 2. * Not its real name. One of the most unusual features of Alpha field are the'phase switch wells'.
Defining fluid contacts(GWC/OWC/GOC) is one of the major variables for defining the initial hydrocarbons in place. In exploratory wells RFT/MDT is often used to define OWC/GWC. In defining contacts static capillary-buoyancy equilibrium is assumed. There is ample field evidence that many of the existing reservoirs are actively being charged from the source rocks. Under these conditions the assumption of static fluid distributions may not be valid and dynamic conditions should be used for defining the fluid distributions and the contacts.
This paper defines the fluid distributions and fluid contacts for dynamically charged reservoirs. The method is based on the recently proposed Dynamic Theory of Hydrocarbon Migration and Trapping. The results of numerous numerical simulations show that assuming static saturation profiles may not be valid for reservoirs having active influx of fluids into them. This is true even at very small influx rates (10-9 m/s-10-14 m/s). The pressure profiles for the static case (no viscous forces) are compared and contrasted with the dynamic pressure profiles. The dynamic pressure drops can be explained on the basis of Darcy's law and relative permeability effects under extreme saturations. These pressure drops are then used to calculate the saturation distribution in the hydrocarbon column and the transition zones. The results show that if the assumption of static equilibrium is used for the dynamically charged reservoirs it will lead to the underestimation of the initial hydrocarbon in place. The non-equilibrium effects can also explain free water production from zones far above the transition zone, expected, on the basis of static assumption. The interpretation of MDT data under both static and dynamic conditions is also discussed.