FLUID INCLUSION STUDIES OF PROMINENT NATURAL FRACTURES IN THE NEW ALBANY SHALE, KENTUCKY, USA

The Middle to Upper Devonian New Albany Shale is an organic-rich black shale succession that has been of economic interest since the late 1850s for its gas productions. Natural fracture sets have been observed in this succession, though little research has been conducted to determine their origin. With renewed interest since the advent and use of hydraulic fracturing and horizontal drilling, it is of particular importance to investigate existing fractures in the New Albany Shale. These fractures are from a few centimeters to more than a decimeter in width, filled with quartz and dolomite, and locally contain pockets of bitumen that must have been part of the fluids that passed through them from underlying stratigraphic intervals. The dominant fracture set is oriented NE and the conjugate set is oriented EW, consistent with the NE trending Wabash Valley fault system and the EW trending 38^th parallel lineament. The fractures can be seen throughout the New Albany Shale, but are particularly prominent in outcrops near the Cincinnati Arch. Vein morphology has been affected by post-vein compaction of the New Albany Shale. The veins in the lower Blocher member appear strongly contorted, whereas veins in the overlying Camp Run and Clegg Creek members have been “telescoped” by compaction. Fluid inclusion analysis was initiated to determine the type and temperature of fluids that created the veins. Using a Linkam THGMS 600 heating-cooling stage, preliminary analysis shows that primary and pseudo-secondary fluid inclusion assemblages exist around and in the quartz crystals. Fluid inclusions range in size from 1 micron to 30 microns, and daughter minerals, predominantly halite, are present in the larger inclusions. No gas bubbles have yet been observed in our preliminary sample set, but this could change once a larger sample set is examined. At the moment, absence of gas bubbles is interpreted to indicate comparatively low fluid temperatures of 40°C or under. Further analysis will address the possibility of multiple episodes of fluid expulsion and vein formation in the New Albany Shale.