Correct sampling of gas condensate reservoir with liquid drop around the well
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In gas-condensate system for an accurate engineering and science computations such as reserves estimation and well testing and analysing a concrete knowledge of phase and fluid phase behaviour is very significant. In typical gas-condensate reservoirs with the decrease of the flowing bottom-hole pressure below the dew point dramatic decrease in gas production occurs. In presence of high pressure and temperature, there is a much higher tendency of complex organic molecules degradation. The conversion of these complex organic molecules into gas-condensate is highly dependent on their burial depth i.e the higher burial depth the higher probability of conversion. The gas-condensate reservoir contains only small part of heavier components but consists mainly of lighter components and methane. But looking in a general way, during degradation of organic complex molecules higher proportions of light HC components occur in deeper reservoirs. In most gas-condensate reservoir cases variation in the composition with time may tend to make some confusion in understanding phase and flow behaviors. In this study, we have used a single-layered, radial and two-dimensional gas condensate and black-oil reservoir models and we have performed both compositional and black-oil isothermal flow simulations. As most studies inform in low permeable gas condensate reservoirs once the pressure drops below the dew-point pressure, then getting accurate fluid sampling is highly challenging. One of the minor observations in this study was that the producing OGR stabilizes quickly below the initial OGR throughout the entire infinite-acting period as long as we kept avoiding BHP from going below the targeting minimum BHP in order to prevent the sharp rate depletion. The major aims of this thesis were make some investigations on how to test a gas-condensate and oil reservoirs in such a way that could give us a correct rate and to observe at which rate we should take our sample. We have concluded that when a liquid dropout from a gas the LGR will always decrease in dependent of the rate. Therefore, the safe way to precise sampling is at a lower rate.
Master's thesis in Petroleum engineering