Fault and Fracture Network Analyses and Modeling in a Challenging Complex Geological Environment - Paleozoic Tight Reservoirs in Algeria
Authors: van Dijk Janpieter , Ajayi Ayodeji Temitope , De Vincenzi Luca , Ellen Helby , Guney Hasan , Holloway Philip , Khdhaouria Mourad , Mcleod Ian Steward 
Published: January 2020

A fully integrated multidisciplinary and multiscale workflow has been applied, using up to date technologies and introducing two new technological components, to investigate upon deliverability of already discovered and proven resources and explore for new reservoirs and prospects in the Palaeozoic of Tinrhert (Ilizzi-Berkine Basin) and M'Sari-Akabli (Ahnet Basin) Blocks (Algeria).

Data involved are seismic mapping and depth modeling, seismic attributes processing, well log correlation, image log and stress field analyses, core data and remote sensing data analyses. Two completely new approaches are outlined in this paper which regard data driven DFFN modeling on 3d seismic data, and multiscale treatment of remote sensing data on fractures and faults.

Various semi-automated 3d seismic attribute analyses techniques were applied to enhance the visibility of seismic and subseismic fault and fracture zones. Variance/coherency extraction plus "ant tracking" (with application of specific shadow zones) were performed on a reprocessed 3d seismic volume. The special data driven technique FD5D was applied to these observations in order to generate data-driven 3d Discrete Fault and Fracture Networks (DFFN) on a subseismic scale. These models permit to evaluate the connectivity and heterogeneity of small faults, major Highly Persistent Fractures (HPF), and Damage Zones or Fracture Corridors, that can be components of flow in the reservoir and contributing to compartmentalization or connectivity on reservoir block / drainage volume scale.

The Tassili area of the Hoggar Massif (southern margin of the Ilizzi Basin) serves as an analogue for the Paleozoic Reservoirs. An extensive multiscale analysis was performed on remote sensing images of the area to obtain information on the fracture and fault network properties. Thousands of fractures have interpreted over a large area and over a large-scale range (m's to 10's of km's) involving special newly designed techniques, focusing on orientation and size distributions. The result of this new approach indicates a clear distinction between the mathematical properties embedded in the fracture/joint population and those that characterize the fault population both in size and orientation. Orientation analyses clearly shows that fault distributions are partially related to reactivated and linked joints whereas most of the joint population is pervasive but not represented as faults. Size analyses show at least two distinct Power-Law distributions. This underlines that care should be taken when integrating the various segments of the size distribution in the generation of predictive models on a well scale.

The multidisciplinary and multi-scale approach, using and evaluating numerous crucial parameters from different sources, provides a sound basis for the future planning of exploration, appraisal and development wells in this challenging subsurface environment which shows multiple stacked reservoirs characterized by dual porosity and dual permeability with highly complex three-dimensional connectivity and heterogeneous drainage volumes.