Water Blocking Damage Evaluation and Mitigation Method in Tight Gas Reservoirs

A substantial volume of aqueous fluid is held in the pore throat of tight sandstone gas reservoirs due to poor porosity and permeability, complicated clay minerals, and pore structures, causing water lock and affecting gas well productivity. As a result, clarifying the water lock damage law of tight sandstone reservoirs is critical for improving gas well productivity. This research explains the pore structure characteristics of tight sandstone reservoirs and uncovers the water lock effect and reservoir damage process under various effusion saturations using constant velocity mercury injection and water lock damage experiments. On this basis, the productivity equation for fractured horizontal wells is created, taking into account slippage, stress sensitivity, and the water lock effect. The reservoir flow law and its impact on productivity in the presence of a water lock are investigated. Moreover, at last, the water lock release formula suitable for the target reservoir is chosen based on the actual reservoir features. Water saturation and reverse effusion had the greatest impact on permeability, according to the findings. Simultaneously, when comparing the productivity change law under various influencing circumstances, it can be shown that the water lock effect is the most important component causing the loss of gas well productivity, and it is something that should be considered in actual production. Lastly, the water lock release experiment demonstrated that introducing a variety of chemicals into the formation is the most effective method of repairing water lock damage. Among them, the 0.9% FS-3100 + 5% hydrofluoric acid +5% clay stabilizer can increase the core permeability by about 10.47 times. To summarize, this work describes the features of water lock damage in tight gas reservoirs and proposes effective water lock removal techniques, which can provide some theoretical advice for tight gas reservoir development.

Automated summary

The water lock phenomenon in tight sandstone gas reservoirs has a significant impact on gas well productivity. Understanding the mechanism of water lock damage is important for improving productivity. This study investigates the pore structure characteristics and water lock effect in tight sandstone reservoirs. A productivity equation is developed, considering slippage, stress sensitivity, and the water lock effect. The study also explores the reservoir flow law and its impact on productivity. Experimental results show that introducing chemicals into the formation is an effective method for repairing water lock damage.