Explicit-implicit representations of naturally fractured reservoirs

Abstract

Naturally fractured reservoirs (NFR) are highly heterogeneous and pose significant challenges for flow modelling. Fractures can be represented implicitly or explicitly in reservoir models. However, it is often unclear which representation should be used. In this work, we consider two different approaches to decide how NFRs should be modelled. First, the Embedded Discrete Fracture Model (EDFM), which explicitly represents fractures, is used to run high resolution simulations on a test model representative of a small sector in a Latin American gas field; these simulations demonstrate how EDFM may be used to gain an understanding of the flow dynamics in the field, which then allows further informed modelling decisions to be made. In a second approach, using EDFM studies performed on stochastically generated and outcrop-based fracture networks, a workflow is constructed to assess the accuracy of Single Porosity (SP) hybrid models which represent the matrix and fractures below a partitioning size as a continuum. The workflow makes use of flow based upscaling to determine a threshold partitioning size beyond which SP hybrid modelling becomes inaccurate. While upscaling can be performed numerically for all fracture networks, the Effective Medium Theory is proposed as an efficient analytical upscaling tool for uncorrelated elliptical fractures.