Model for prediction of edge-water breakthrough time in reservoirs with edge water with consideration to effects of gravity and non-Darcy effect of gases

All existing models for prediction of edge-water breakthrough time are based on horizontal plane. However, actual gas reservoirs always have certain dips from the horizontal plane. It is necessary to consider effects of the gravity. According to the theories for gas-water flow mechanics, and with consideration to dip angles, non-Darcy flow effects of gases, gas/water mobility ratios, distances between gas well and the edge water, and other factors, a new model for inclined gas reservoirs with edge water was built. Then, sensitivity analysis was performed for the new model. Compared with existing prediction models, the new model can predict breakthrough time of edge water closer to actual time. Sensitivity analysis shows that edge-water breakthrough time is in quadratic parabola relationship with dip angles. The maximum edge water breakthrough time can be observed at the dip angle of 90°. The edge-water breakthrough time is in power-function relationship with the distance between the gas well and the edge water. With such distance of 500 m or more, the edge-water breakthrough time increases 7 d for every 100 m. Moreover, the edge-water breakthrough time is in inverse relationship with both gas well productivity and non-Darcy factors of relevant gases. In earlier stage of development, the breakthrough time of edge water reduces up to 90%. When the gas well is flooded, effects on breakthrough time of the edge water are ignorable. Furthermore, the edge-water breakthrough time is in liner relation with both gas/water flow rate and reservoir thickness. The edge-water breakthrough time increases 30 d when the gas/water flow rate is doubled, and increases 49 d for every additional meter in reservoir thickness. It is very important to determine these parameters accurately in early stage of gas well production. The research results can provide necessary technical supports for high-efficiency development of gas reservoirs with edge water.