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Fractured basement reservoirs in Southern Sumatra are typically combinations of intrusive and metamorphic terrains. The metamorphic host rocks contain a variety of unique mechanical deformation styles and thus not all host rocks fracture the same. The extreme members are the intrusives granitic reservoirs with their interlocking crystalline structure which rupture through the crystalline fabric resulting in multiple fracture orientations depending on the orientation and intensity tectonic events. The metasediments however, have a variety of preexisting fabric weaknesses. Meta-pelitic lithologies (mostly phyllites in this paper) represent the opposite end of the spectrum to the granites and release slip movement along phylliosilicate layers. Fractures in the pelitic lithologies are dominated by slippage along foliation or kink bands unless these units have been embrittled by other processes. Reservoirs developed where a phyllitic section is dominant may exhibit complex behaviors depending on proximity to intrusives and structural position. Major accumulations of hydrocarbons are contained in the fractured metasedimentary reservoirs in the South Sumatra Basin. Phyllitic reservoirs are not all the same. Several of these fields where phyllites is the dominated reservoir lithology are influenced by a granitic intrusives. Those lying in proximity of an intrusive reservoir are advantaged through the interaction of fluids (and heat) from the intruding mass. It should be noted that primary silica content of the phyllites is likely to have a degree of influence on how it breaks and tectonic deformation impacts these rocks depending on how brittle they are. Core demonstrates the influence of hydrothermal embrittlement of the metamorphic section near these intrusives. Silica was injected into the reservoir and effectively locked the phyllitic slip planes and caused the reservoir to fracture as a brittle reservoir. Evidence is abundant in the core where individual quartz crystal lined veins occur about every 10 cm. In contrast, wells over 8 kilometers away, while in pressure communication to a 100MMCFGPD+ well (only producer in the field), produce at subcommercially rates. Here the phyllite was not influenced by either hydrothermal or strong tectonic deformation. Where no granite was present, structures have been drilled at the apex of large structural folds have also failed to produce commercial hydrocarbon rates due to the mechanical deformation style of the micaceous phyllite dominated section. While a well was drilled near the highest accommodation point of the structure the metasedimentary section dominated by phyllites was remarkably unconnected and would not sustain commercial rates. Variations of original brittleness will reflect in reservoir continuity and performance. While noting that increasing brittleness of phyllites through intrusive process creates better reservoir connection the open fractures along the schistocity planes of weakness may provide a secondary storage facility that would be very sensitive to principle stress sensitive.