Prediction of marine shale gas production in South China based on drilling workload analysis

Abstract

The marine shale gas resource in South China is abundant, but the existing conventional methods cannot meet the needs of predicting the future production development of shale gas. With the marine shale of the Lower Silurian Longmaxi Fm in this region as an example and based on its development potential, the development features of the existing shale gas resources were analyzed. It is considered that the Longmaxi shale gas accumulation zones in the Sichuan Basin and its neighboring areas contain resources of about 17.4 × 1012 m3 and recoverable resources of about 2.9 × 1012 m3. In particular, the shale gas above 3500 m underground is the main body for recent development targets, with a potential production scale about 300 × 108 m3. On this basis, the development features of foreign and domestic shale gas wells were studied and the drilling workload analytical method for the prediction of shale gas production was established: (1) the initial production of a single well can be used to characterize the productivity of the shale gas well, and its test production is approximate to its initial production. Due to the similarity of decline rate among shale gas wells, the single-well estimated ultimate recovery (EUR) value of a single well can be roughly speculated from its initial production, thus the production scale of a shale gas field can be speculated according to the analysis of drilling workload; (2) currently, the expected test production of South China marine shale gas is 17.6 × 104 m3/d, and the predicted single-well EUR value is roughly 1.5 × 108 m3. It is concluded that the marine shale gas in South China represents high initial production of a single well, high declining rate, longer production cycle and the drilling workload is closely related with the production of a shale gas field. Therefore, the analysis of drilling workload shows better applicability to the evaluation of shale gas production. Based on this method, the shale gas production of the Sichuan Basin and its neighboring area in 2020 was estimated to be about 200 × 108 m3