Adapting Fracture Corridors and Diffuse Fractures in Single Porosity Model of Ujung Pangkah Carbonate Reservoir

Abstract

A practical method to adapt fractures both micro and macro as flow enhancing properties in a single porosity model is introduced to simulate Ujung Pangkah fractured carbonate reservoir. This approach is taken because dual porosity modeling attempt fails to explain the behavior of many wells which experience early water breakthrough and/or excessive water production in Ujung Pangkah field. The enhancement factor term is used to define the degree of permeability enhancement by diffuse or micro fractures. At well location, the enhancement factor can be determined by the ratio of production test to the production of matrix-only model. The enhancement factor 3D distribution is derived from well data and seismic minimum curvature attributes as trend. Fracture corridors correspond to macro fractures in the order of meters extending vertically and/or laterally. As normally scattered spatially, fracture corridors cannot be modeled in a discrete fracture network model which is the integral part of dual porosity model. Some wells show behavior anomalies, such as rapid, early water breakthrough with excessive water production in unlikely location. It is observed that the location of these anomalies coincide with the fracture lineaments derived from the seismic incoherency attribute. As the fractures are well characterized, diffuse fractures as permeability enhancement and fracture corridors as high permeability streaks, the further improvement of history match is then easily achieved by calibrating two other key parameters; relative permeability curves and aquifer strength. The relative permeability is calibrated to the shape of fracture relative permeability. Oil rate match is greatly improved. Water rate match is achieved by placing adequate aquifer strength. Reservoir dynamic of Ujung Pangkah carbonate fractured reservoir can be simulated as a single porosity model with permeability enhancement adapted from two types of fracture distribution. Diffuse fractures enhance the overall permeability and fracture corridors dominantly influence flow dynamic in certain local area. Compared to dual porosity model, adapting fractures as permeability enhancement in single porosity model is more practical, more efficient in simulation run time – computational cost.