New Predicting Method of UGS Well Performance in Strongly Heterogeneous Gas Reservoir

Gas well performance is one of the key indexes to determine the working gas volume, peaking capacity and the economy of the underground gas storage. The reconstruction of deep medium-low permeability depleted reservoirs in China usually more costly because of the greater difficulty in well drilling and completion and the higher requirement of tough cementing. Therefore, the gas well performance and accuracy of its prediction have a decisive influence on the technical feasibility and economic benefits of storage construction. This paper compared the actual performance and its predicted counterpart of the H gas storage-a typical strongly heterogeneous gas storage in China-and found that the difference between them was significant. Besides, wells less affected by water invasion and drilling damage generally have higher performance than designed after multiply huff and puff. The analysis showed that the fundamental reason for the deviation is that the performance equation based on the “low speed” development state has been directly used to predict the performance of gas well under “high speed” injection and production condition of gas storage. Based on this, a new method combined numerical simulation and reservoir engineering to predict the performance of UGS wells was put forward, it can convert the actual test data in development state and establish the productivity equation of injection-production state by using the functional relationships and typical curves about the two states. Compared with the previous method, the new method applied to typical storages such as H and X can drastically improve the accuracy of the prediction, scientifically guide the construction and optimally allocate the later production and injection.