Experiment and prediction for dynamic storage capacity of underground gas storage rebuilt from hydrocarbon reservoir

Understanding the variation in dynamic storage capacity is significant and meaningful to design operation strategy of underground gas storage (UGS). However, there is a lack of methods to recognize and predict dynamic storage capacity of UGS. This paper introduces a novel experimental system to directly measure rock porosity under different effective stresses. W gas storage, the biggest UGS in Central China, was taken as a case to discuss trend characteristic of dynamic storage capacity. Then a model for predicting dynamic storage capacity of UGS was further developed based on experimental results. Lastly, the prediction model was used to evaluate dynamic storage capacity after 30 operation cycles in W gas storage. Results show that porosity of reservoir rock, as well as dynamic storage capacity of UGS decreases with cyclic stress, and the loss gradually reduces with alternating stress cycle. In addition, after 30 operation cycles, the loss of dynamic storage capacity is about 1.34 × 108 m3, 1.40 % of total initial storage capacity in Zone Z1 of W gas storage, and about 0.11 × 108 m3, 1.51 % of total initial storage capacity in Zone Z2. Specially, modelling flow in this work is not only suitable for W gas storage, but also can be used to study any UGSs rebuilt from hydrocarbon reservoirs.