Modeling of Gas Condensate Wells with and without Hydraulic Fractures




Mohan, Jitendra

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A typical problem associated with gas condensate wells operating below dew point is that of condensate blocking. As the pressure near the well falls below the dew point, liquid drops out and condensate starts accumulating. It reduces relative permeability to gas and hence may cause significant decline in the well productivity. The main objective of this thesis was to study the impact of hydraulic fracturing in gas condensate wells. A single-well model was simulated using GEM, CMG's compositional simulator. The results show that a vertical fracture improves the conductivity of a gas condensate well significantly, and this increase depends on many factors. Effect of such factors such as non-Darcy flow, capillary number was simulated. It is demonstrated that non-Darcy flow can decrease the well productivity by a factor on the order of 2 to 3. In addition, a sensitivity analysis of various parameters such as fracture dimensions, fracture conductivity, reservoir permeability, drawdown, gas end-point relative permeability was done. The results showed that productivity improvement is highest for low permeability reservoirs. The well productivity is sensitive to dimensionless fracture conductivity when it lies in the range of 0.1 to 10 Furthermore, an analytical expression was derived for optimum fracture length, which included the effects of non-Darcy flow and condensate banking. The results were in good agreement with the simulation results. Effect of various factors such as fracture permeability, reservoir permeability, gas composition and condensate bank width, was studied. It was shown that the optimum fracture length required for flow above dew point was less than that for flow below dew point. For low permeability reservoirs, a longer and narrower fracture was found to be preferable to a shorter and wider fracture. The optimum fracture length was found to increase as the width of condensate bank increased. Finally, a comparative study was done on the performance of unfractured horizontal wells and fractured vertical wells. Sensitivity of parameters such as vertical permeability, reservoir permeability was studied. In addition, effect of non-Darcy flow, capillary number, and heterogeneity was also analyzed. The results show that the productivity of the horizontal wells was greater than that for the fractured vertical wells by a factor on the order of 2, even at low values of vertical permeability. The effect of non-Darcy in the horizontal well was found to be very insignificant, and the effect of capillary number was quite considerable. Heterogeneity was found to have a significant effect on the productivity of the horizontal well for certain cases.


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