This leads to under-utilization of existing storage resources and consequent competitive restrictions on particular projects. In many instances the pressure in a gas storage reservoir can be safely increased if the geomechanical behavior of the reservoir and overburden is well characterized. Two basic geomechanical processes limit maximum operating pressures in gas storage reservoirs. Tensile fracturing can occur when the pore pressure within a formation is increased above the minimum in situ stress. The hydraulic fracture pressure provides an absolute limit to maximum storage reservoir operating pressure, as it is necessary to avoid fracturing through the caprock and allowing gas leakage into overlying permeable formations.
Minimum stresses are best determined from hydraulic fracture tests in a formation.
When this information is unavailable, then regional stress data can often be reviewed to provide estimates of stresses. Another constraint on gas storage operations is the pressure at which faulting or substantial bedding plane slip may be induced in the reservoir or overburden. Such overburden damage can be induced by two mechanisms. In the first type of process, pore pressure changes within an existing fault plane may modify the effective normal stress sufficiently to activate the fault. In the second type of faulting process, reservoir compaction and dilation can induce shear stresses in the overburden, resulting in rock failure or slip of weak zones, along existing faults, or along bedding planes.