Estimation of matrix flow contribution in naturally fractured reservoirs

Naturally fractured reservoirs can hold large hydrocarbon resources, but the characterization of naturally fractured reservoirs is a recurring challenge for the oil and gas industry. The purpose of the present study is to develop a more accurate approach for estimating the fluid flow in a naturally fractured reservoir.

The project’s objective is to utilize actual naturally fractured carbonate reservoir data to develop a more clearly defined approach for estimating matrix flow contribution in naturally fractured reservoirs (NFRs), and to develop a new NFR classification system that recognizes the matrix and micro-fracture zone contributions separately.

Naturally fractured carbonate reservoirs (NFRs) account for a majority of the world’s proven oil reserves (~60%), as well as a significant portion of proven gas reserves (~40%). NFRs are mostly modelled as dual porosity systems with a separate matrix and fracture porosity, each with their own reservoir attributes. In accordance with the most commonly applied NFR classification system, e.g. Shell (ca. 1955), NFRs are often categorized by types (1-4 with 1 being almost entirely fracture volume storage and overall fracture dominated flow and 4 being less in fracture storage and a majority of flow contribution from the matrix). For recoverable volume estimates, current industry practice is to apply individual recovery factors to the matrix and fracture systems according to these NFR categorizations utilizing mostly worldwide analogue field data both in stochastic volumetrics and numerical modelling.

A majority of NFRs are Type 1 and Type 2 where there the overall field’s recoverable volume can be significantly impacted by small estimation differences of matrix recovery.  For example, a Type 1 NFR may have a 10/90 split of fracture to matrix storage, but a 90/10 split of fracture to matrix recovery. Due to the significantly larger matrix in-place volumes, only a 10% incremental increase in matrix recovery factor (20% instead of 10%) would result in a 50% increase in the field’s overall reserves. NFR’s matrix characterization (including the poorly understood micro-fracture zones) must then be better modelled in order to mitigate this material uncertainty. 

Contact

Justin Brand Ferrell
DTU Chemical Engineering

Contact

Alexander Shapiro
Associate Professor
DTU Chemical Engineering
+45 45 25 28 81