Effects of water invasion law on gas wells in high temperature and high pressure gas reservoir with a large accumulation of water-soluble gas

Abstract

A high temperature and high pressure (HTHP) gas reservoir with a large accumulation of water-soluble gas contains a large amount of dissolved gas in formation water. The dissolved gas in the formation water will be released due to formation pressure depletion in the production process. At present, few researches have been done on water invasion law of gas wells regarding the released dissolved gas, especially when the change rule of water and gas is not clear in porous media after the release of water-soluble gas, which leads to the unclear water invasion law and the gas reservoirs cannot be developed efficiently. In this paper, a visualization sand filling tube is used to conduct experiments to study the effects of the dissolved gas on the law of the gas-water contact (GWC) changes in the water-soluble gas release process. The experimental results show that the release of dissolved gas leads to a GWC rise at the beginning of the depressurization process. After the pressure drops to a lower level, the GWC will decline due to a large amount of dissolved gas being released from formation water. Subsequently, numerical simulations are performed to study the effects of different solubilities of natural gas, the gas production rate, the aquifer size, and stress sensitivity on the water invasion law of the gas well. The simulation results show that a greater solubility of natural gas, a higher gas production rate, a larger aquifer size, and the existence of stress sensitivity all lead to stronger bottom water coning and an early water break-through. For the non-coning region, a greater solubility of natural gas will lead to a slower rise in the GWC. The simulation results show that the water invasion velocity with water-soluble gas is faster than the velocity without water-soluble gas.