Paragenesis and Multi-fracture System in Jurassic Barsarin Formation: Implications from Various Burial Settings, NE-Iraq

Generation of fracture systems and geofluid evolution in shallow and subsurface environmental conditions play a critical role in various geological processes and petroleum applications. This paper evaluates comprehensive data to provide a deep understanding of multi-fracturing systems dissolved/filled by various cement phases related to different tectonic settings and the influx of diagenetic fluids in near-surface and subsurface settings. This study utilized intensive field observation and an optical microscope to track the paragenesis of the targeted formation and fracture stages in the Jurassic interval. The study recognizes five main types of fractures: (1) FI generated during surface or near-surface conditions; the timing of initiating FI is not older than low-amplitude stylolite (LAS); (2) FII formed in shallow burial diagenesis and was coeval with late diagenetic stage; (3) FIII in-situ fractures formed in the subsurface conditions coinciding with high-amplitude stylolitization (HAS), (4) FIV fracture filled by calcite cement with plenty of solid bitumen fluid inclusions; and (5) FV-filled dolomite cements. The characteristics and appearance of dolomite crystals, corrosion, suture contact between saddle dolomite/calcite grains, and tightly compacted grains are directly linked to the increasing burial weight of overlying sedimentary rocks during the “Mesogenesis Phase." In summary, the findings add new insight, as the fractures act as essential conduits and barriers in hydrocarbon migration and accumulation through various geological processes, from their formation during deposition to their evolution and the fracturing significant in post-depositional settings. The recognition of how these fractures originated enables more effective exploration and production strategies in hydrocarbon reservoirs.