Chris McKeown¹

(1) Midland Valley Exploration Ltd, Glasgow, AK

ABSTRACT: The Use Of Structural Modelling In The Simulation Of Naturally Fractured Reservoirs

Naturally fractured reservoirs are increasingly forming a significant proportion of operator's portfolios. The simulation of such reservoirs requires an understanding of the spatial distribution of reservoir units and their associated petrophysical properties; porosity, permeability, water saturation, relative permeability and capillary pressure. Such information is difficult to obtain, compounded by the necessity of upscaling the petrophysical properties from the multimillion cell geo-model to the multithousand cell simulation model.

Models of fractured reservoirs additionally require information on the likely recovery processes occurring between the unfractured material (matrix) and the fracture network. These processes are a function of the matrix and fracture petrophysical parameters, which are in turn related to the fracture density, connectivity, orientation and distribution.

Fracturing in natural systems forms as a result of geological processes. Reservoirs are subject to spatial and temporal evolution of strain paths and stress history. The structural evolution of a reservoir can be modelled and the resulting strain/stress data used to build a geologically realistic fracture network. These forward modelling techniques can characterise the fracture network in the whole reservoir, improving on the current techniques of interpolation between wells.

This paper presents a method of generating naturally fractured reservoirs honouring the deformation history. Such fracture networks may be exported directly to single or dual porosity reservoir simulation models. The fracture density, connectivity, orientation and distribution can be used in the calculation of fracture permeability, porosity, volumetrics and the matrix-fracture transfer potential.

This method significantly reduces risk of error in simulation by better constraining the input data.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado