Abstract
Condensate banking is one of the most challenging problems in shale gas exploitation as it acts as flow choke around hydraulic fractures reducing the drainage of shale matrix. Thus, fracture spacing optimisation is a key element of shale gas and condensate field development. For shale gas reservoirs, more accurate models are needed to describe the gas-condensate flow in the shale matrix where the flow mechanism and phase behaviour are different from those of conventional reservoirs.
In this paper, new models developed for flow behaviour and phase behaviour to estimate well productivity as function of time are presented. The Knudsen flow was used to model apparent gas permeability in shale matrix as a function of pressure and pore size distribution. A modified Peng-Robinson EOS was used to evaluate the condensate saturation in the matrix under capillary pressure effect. A semi-analytical well model was also developed to evaluate well productivity under constant pressure.
The results show substantial difference and impact with the application of Knudsen flow when compared with conventional Darcy law. Using conventional Darcy flow instead of Knudsen flow for gas-condensate reservoir development can lead to a underestimation of well production up to 30%. Although capillary pressure has an effect on phase behaviour its impact on well production is insignidficant.
This study shows the importance of using flow behaviour deviation model in well completion optimisation for shale gas-condensate fields. Using conventional flow models can undermine the economic viability of gas-condensate shale reservoirs by underestimation of optimum fracture spacing.
