钻井工作量分析法预测中国南方海相页岩气产量

中国南方海相页岩气资源丰富,但已有的常规方法不能满足对未来页岩气产量发展的预测。为此,以该区下志留统龙马溪海相页岩为例,基于其开发潜力,分析了现有页岩气资源的开发特征,认为四川盆地及邻区龙马溪组页岩气富集区资源量达17.4×10~(12) m~3,可采资源量为2.9×10~(12) m~3,其中埋深3 500 m以浅的页岩气资源是近期开发的主体,具备建成约300×10~8 m~3的产量规模。在此基础上,研究了国内外页岩气井的开发特征,建立了页岩气产量预测钻井工作量分析法:(1)单井初产值可表征页岩气井产能,测试产量可近似为初产,由于页岩气井递减率相似,由单井初产值可大致推测单井EUR(最终可采储量)值,再根据钻井工作量分析即可预测页岩气田产量规模;(2)目前南方海相页岩气测试产量期望值为17.6×10~4 m~3/d,单井EUR预测值约为1.5×10~8m~3。结论认为:中国南方海相页岩气井单井初期产量高、递减快、生产周期较长,钻井工作量与气田产量密切相关,因此钻井工作量分析法对页岩气产量估算具有较好的适用性。利用该方法估算2020年四川盆地及邻区页岩气产量约为200×10~8 m~3。

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

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 3 500 m underground is the main body for recent development target, 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 Estimated Ultimate Recovery (EUR) value of a single well can be roughly speculated from its initial production, thus the production scale of 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.