Properties of gas-condensate reservoirs are particularly difficult to study due to the composition and phase changes of light components that occur during the reservoir depletion. At the first stage of their discovery, these reservoirs behave like gas reservoirs during depletion. Once the dew point pressure is reached at reservoir conditions of pressure and temperature a retrograde condensation phase develops in the reservoir. Liquid condensation in the formation can result in severe loss of well deliverability and therefore of gas and condensate recovery, which will certainly lead to a loss of income.

In this study, the performance of horizontal wells and vertical wells in gas condensate reservoirs is investigated under various depletion schemes. The expected low drawdown pressure for horizontal well, compared to vertical well for the same flow rate, considerably reduces retrograde condensation. A reservoir simulator is used to compare liquid saturation profiles for horizontal and vertical wells in gas condensate reservoirs. The influence of the horizontal well length section and reservoir thickness on horizontal well productivity, and condensate recovery were also studied. Another factor investigated in this study is the effect of drilling a horizontal well in a gas condensate reservoir that has already been developed by vertical wells.

To illustrate the productivity increase due to the use of horizontal wells in gas condensate reservoirs, Djebel Bissa field (Figs. 1 and 2) data are presented and discussed using a compositional single well model (VIP simulator). The main results of this investigation are as follows: A smaller pressure drawdown for a horizontal well compared to that of a vertical well, eliminates or reduces liquid condensation in the reservoir.

Layers with higher capacity (kh) values contain the most liquid accumulations.

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