页岩气投产井经济最终总可采量快速评估方法——以四川盆地CN区块为例

Fast evaluation method for EUR in producing shale gas wells:An example from CN Block,Sichuan Basin

随着四川盆地页岩气的持续规模上产,四川盆地2019年页岩气新增证实储量(SEC储量)占全部新增储量的一半以上。页岩气投产井证实储量评估以单井为单位,四川盆地页岩气工作量巨大,且对于生产早期的井,评估不确定性大,难以在较短时间对整个区块或气田证实储量做出可靠评估,即快速合理评估全部井最终总可采量(EUR),为气田高效开发反馈有益建议。为此,将分段双曲递减方法与百分位50典型曲线相结合,首次提出了页岩气井最终总可采量的快速评估方法。研究结果表明:①分段双曲递减法对于生产时间短的井,当递减参数选取不当会造成极大的预测偏差;②用百分位50典型曲线分段递减模型参数,能够快速准确预测同一区块生产井的最终总可采量,且精度高。结论认为:快速评估方法简化了大量单井分段双曲递减的工作流程,降低评估工作量的同时合理控制了最终总可采量的误差,适合井组、区块及气田证实储量总量的评估。

With continuous large-scale production of shale gas in Sichuan Basin,newly proved shale gas reserves(SEC reserves)in this Basin in 2019 accounted for more than half of the annual new reserves.As the proved shale gas reserves in producing wells is evaluated well by well,thus evaluation workload is huge.Moreover,for some wells in early production period,the evaluation uncertainty is large,thus it is difficult to make a reliable assessment on the proved reserves of the whole block or a gasfield in a short time.This means to evaluate the total EUR of all the wells quickly and reasonably,and feedback useful advice for gasfield development.For this reason,by combining the sectional hyperbolic decline method with P50 typical curve,the fast evaluation method for EUR in shale gas wells is proposed for the first time.Results show that(1)for one well with short production time,to improperly select decline parameters in the sectional hyperbolic decline method will result in great prediction deviation;and(2)the P50 typical curve sectional decline model can be used to quickly and accurately predict the total amount of EUR in a production well in the same block with high accuracy.It is concluded that the fast evaluation method simplifies the work flow of sectional hyperbolic decline in a large number of single wells,and reduces the assessment workload,and reasonably controls the EUR error at the same time,furthermore,is suitable for assessing the total SEC reserves of a well group,a block,and a gasfield.