Water-gas ratio characteristics and development concepts for water-producing gas reservoirs

Water production from gas wells is a key factor affecting the effectiveness of gas-reservoir development, and it poses serious challenges in terms of increasing the degree of recovery during the waterless production stage and reducing the impact of water production on gas-reservoir development in the middle and later periods. Thus, gas reservoirs must be efficiently exploited on the basis of identifying gas-water layers accurately, defining gas-water relationships, and understanding gas-water production performance. Accordingly, this study analyzes the production characteristics in gas reservoirs with different gas-water relationships, and it summarizes the rules that determine water-gas ratios. The results reveal that the water-gas ratio increases rapidly in the early stage of water production, but after a period of time, it enters a relatively stable state in which it is almost a fixed value. According to the material balance equation, the theoretically calculated water-gas ratio is fully consistent with the production rules for an entire confined gas reservoir. This shows that the reality of gas-well-water production must be faced, and that the development of water-bearing gas reservoirs must accommodate gas and water co-production. The gas-water relationship, water body scale, and reservoir heterogeneity determine the time of water breakthrough and the water-gas ratio. Therefore, we should change the traditional “water fear” concept in gas-field development, aim for an overall improvement in recovery, face up to the fact that gas wells produce water, and coordinate the development of multi-wells for entire gas reservoirs, all of which will achieve the ultimate goal of improved gas recovery.