Technical Paper: Understanding the Interplay of Fractures, Stresses and Facies in Unconventional Reservoirs - Case Study from Chad Granites

Society: EAGE
Paper Number: Tu D201 04
Presentation Date: 2014


This work presents a a case study from Bongor basin, Chad which utilizes the geological evolution approach to effectively characterize unconventional granitic reservoir based on the interpretation performed with borehole images and open hole logs. Interplay of fractures and facies and the impact of the prevalent stress regime have been deciphered from the study wells with the help of borehole images and petrophysical logs. Three main distinct facies were interpreted; Unweathered, Leached and Fractured (Normal and Intensely Fractured sub-facies) granites respectively. Within the leached granite, there exist fault breccia and major faults with two dominant strike orientations; NE-SW and NW-SE. This resulted to the development of secondary porosity within these reservoir zones. The observed granite basement facies, particularly the fractured and leached granites developed good secondary porosity due to differential leaching and fracturing.

The placement of subsequent wells in the preferred leached and fractured reservoir facies bearing fractures that possess the same orientation as the maximum stress depends on several determinants, one of which is the location of the proposed well with respect to the prevalent stress regime attributed to tectonic forces from the Central African Shear Zone arising from the West and Central African Rift system.

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