Abstract
Formation and fracture damage coupled with condensate blockage might significantly reduce the productivity of the hydraulically fractured gas condensate wells. Implicit numerical representation of a hydraulic fracture oversimplifies and disables distinction of individual physically occurring mechanisms causing the well deliverability loss. In this paper, more realistic analysis of production impairment is presented by explicit fracture modelling using an in-house tool. The objective is identification and ranking of the main factors and flow characteristics contributing to productivity drop.
The in-house tool can be characterized as an interface between a fracture design modelling software and a reservoir simulator. An accurate fracture geometry and spatial property mapping is incorporated into a reservoir model via local grid refinement (LGR) generation. An additional functionality of the in-house tool also allowed, based on the fracture report, to determine the initial distribution of the leak-off fluid around the fracture. A mechanically induced damage zone surrounding the fracture was reproduced by permeability/porosity reduction or transmissibility modification on the boundary between the matrix and fracture interface. Permeability modification along with stress-dependent transmissibility option were used to represent the damage of proppant pack on fracture gridblocks.
Explicit and comprehensive numerical representation of the near fracture flow performance was first implemented in a synthetic model. The conducted study revealed that the damage both inside the fracture and in the formation accelerates and enhances the condensate blockage effect. High-velocity capillary number effect within the fracture masked the negative contribution of liquid drop-out on relative permeability curves and can also overwhelm the turbulent non-Darcy flow impact.
To validate the observed phenomena a single well reservoir sector model with explicit hydraulic fracture representation was calibrated against the real production data. Adequate history match of the measured BHP was only possible with dramatic fracture and formation permeability reduction to account for damage processes. Condensate blockage effect caused more than 50% loss of gas flow rate.
