Major gas trends have developed in the Devonian Slave Point dolomite in the Fort Nelson area. The reservoir rock is often fractured and has extremely large vugs, rendering acoustic-type devices virtually useless. Under controlled conditions, neutron logs are superior to acoustic logs since they react primarily to total porosity and the neutron-porosity relationship is less affected by fractures, pore geometry, etc? Neutron-core porosity plots indicate that neutron readings vary logarithmically with porosity, resulting in a straight line. Density logs appear to be reliable for calculating porosities under 10%. Acoustic log versus core porosity plots in the same pool indicate that wide variations occur in matrix velocity and apparent fluid velocity. The plots of any one well may result in a straight line of variable slope, a line of two or three different slopes or even a curve. This relationship is not predictable, therefore, without core control in each well, substantial errors could occur in porosity calculations. Resistivities from induction or laterolog type devices do not approach Ro in water-laden zones, because of abnormally high gas saturation in the water zone. Subsequently, water is produced from zones with a calculated Sw as low as 14%. Because of very high resistivities, greater discrimination between fluids is obtained from laterologs than from induction logs. Laboratory determined values of cementation factor (m) and saturation exponent (n) are necessary for accurate log interpretation in Slave Point reefs.

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