Abstract: Using material balance principle, gas-bearing height and water-bearing height variations in bottom-water reservoir with time are deduced, and the sweep efficiency is approximately determined. Then, based on the equivalent flowing resistance method and vertical critical velocity of bottom water drive, the computational model for critical producing pressure differential for development of gas reservoir with bottom water is derived. Therefore, the variation of decline trend when quantitatively expressing the increase of critical producing pressure differential of horizontal well with time is clarified. Moreover, this paper analyzes the influences of ratio between vertical permeability and horizontal permeability, the difference between water and gas density, the ratio of water to gas viscosity and height of bottom water coning on the critical producing pressure differential. The results could provide theoretical basis for determination of reasonable producing pressure differential and producing rate by horizontal well development of gas reservoir with bottom water.

Key words: bottom-water gas reservoir, critical producing pressure differetial, horizontal well, gas bearing height, recovery efficiency