Underpressured and Overpressured Tight Gas Sands: Ⅱ. Spatially and Temporally Varying Conditions

摘要

This paper investigates the behavior of gas in tight sand aquifers when the shape of the aquifer, its cross-section, permeability, and temperature can all vary along the length of the aquifer. The basic response equation is steady state input of gas under pressure at the lower end of the aquifer and uses Darcy's law for fluid motion in association with buoyancy drive on the gas to determine the gas pressure variations along the aquifer as the lower end aquifer conditions are changed. Both overpressured and underpressured situations can arise, and are sensitive to the variation of parameters describing both the geometry and the physical conditions in the aquifer. Several illustrations are given to show how simple changes can cause different pressure conditions along the aquifer, making it difficult ahead of drilling to know which conditions prevail in a given tight gas sand aquifer.