13. The porosity of a rock sample is 18.5%, and its bulk volume is 85cm3 at the ground level at ambient conditions. The porosity of this sample drops by 20% at a depth of 12000ft. Find the pore compressibility of this sample assuming constant temperature, given that the overburden pressure gradient is 0.95psig/ft. 14. A cylindrical rock sample has a length of 6cm, a diameter of 4cm, and a dry weight of 166.4g. When fully saturated with an oil of density 0.85g/cm3, the weight of this sample is 176.9g. Assuming constant temperature, find: - a) The pore compressibility of the sample, given that 0.2cm3 of oil leaves the sample when a pressure of 3200 psig is applied on it -b) The amount of oil that can be extracted from the sample when a pressure of 2000 psig is applied on it