Core - Hole Correction Tables


For a given core depth, the Core to Log table give a depth in the down the hole logs that correlates with a depth marked on the cores by the drillers. This was produced first by patching together the descriptive logs core no. 1 and core no. 2 for the Weston, Somerset, Rutgers, Titusville, Princeton cores. First the core logs from core no. 1 and core no. 2 were patched together by using at least one lithologically distinctive bed shared between cores. The depth values for the no. 2 core was then adjusted to match that of the correlative parts of the no. 1 core. For the Core depth was then correlated to stratigraphic depth by using distinctive peaks in the Amoco SHADS core natural gamma logs (usually black shales) and down hole gamma logs (Goldberg and others, 1994) to correlate the core to the core hole. The depth scale of the cores correlated to the depth scale of the hole. This procedure is necessary because of the inevitable expansion of the core and small amounts of core loss during the coring and retrieval process.


For a given bore hole log depth the Log to Stratigraphic Depth Table gives a stratigraphic depth that correlates to the log depth. The bore hole log depth (equivalent to distance from surface) was converted to true depth using hole deviation surveys, and true depth was converted to stratigraphic depth using the dip meter survey. In the case of the Weston cores, thin, distinctive shale beds in the core were directly correlated to natural gamma spikes in the hole logs because the SHADS system was not available.


The amount of modification to the core depth is in all cases small, amounting to a maximum of 0.7% (Princeton cores) and averaging 0.5%.