A sandstone formation in the Rocky Mountains region is at a depth of 10,000 ft from the surface. The average porosity, of few cores, measured in the lab is 20 %. The lab measurements were performed without confining pressure. What is the estimated initial porosity at reservoir conditions (i.e. with confining pressure)? What is the porosity after the reservoir pressure declined to 1,100 psi. Comments? Hints. Assume TDS=8% to estimate hydrostatic pressure.