New Model for Production Prediction of Shale Gas Wells

In shale reservoirs, pores and fractures are developed, and the seepage mechanism is complicated. The gas well estimated ultimate recovery (EUR) is difficult to be determined. The existing methods are highly dependent on production data from shale gas wells, and they cannot accurately predict the EUR of a single well with little production data and a long production time. By combining the indoor depletion development simulation experiment with in situ production data, a new power function decline model of the daily gas production and production time was established. The production process of shale gas was divided into two stages: the fracture network control stage and the matrix control stage. During the fracture network control stage, both the daily gas production and the daily water production increased rapidly and then decreased rapidly, with large fluctuations. During the matrix control stage, the daily water production gradually decreased and approached zero, and the daily gas production exhibited a power function decrease. The calculation results of the model are highly consistent with the actual production decline curve of shale gas. This demonstrates that the simulation experiment can reflect the decrease in the actual production well. The established model can eliminate the uncertainty in EUR calculations caused by insufficient actual production data. The EURs of 25 wells in the Weiyuan area have been calculated for 4 consecutive years. The overall error between the EUR calculated by the model in 2017 and 2018 and the EUR of the development plan is less than 5%. Owing to the development process, the EUR calculation results tend to increase year-by-year. It should be noted that the late production of shale gas well is worthy of attention.