Fracture Fill

Today we processed rock core to a depth of 1538 ft.  Over the last couple days, the drillers have had to pull up some of the drill string when the torque gauge on the rig indicates that loose material is accumulating on the outside of the pipe.  When they then advance back down the hole, they drill through the rubble that has fallen in and then the entire pipe turns more smoothly as the drill bit advances downward.  This is called a "wiper trip," because the drill string clears debris to the bottom of the hole somewhat like how a windshield wiper clears water droplets off a windshield. 

Above is a photo of the "fracture fill" that I mentioned yesterday.  We've been seeing quite a bit of this material, the fill itself is the brown band in the middle of the photo.  If you look closely, the fill appears muddy and a bit smeared.  This material can at times be quite solid because it has been compacted by all the weight on top of it, but it is sediment rather than solid rock.  It seems that fine-grained silt and mud has been washed into some fractures by groundwater and then compacted in place.  There are still plenty of fractures that have no fill in them, but this fill can help hold otherwise broken rock core pieces together.  As we progress deeper, it will be interesting to see if this fracture fill material persists and if it will help hold together the core even more.