致密砂岩气井递减参数的合理取值

Reasonable determination of decline parameters of tight sandstone gas wells

致密砂岩气藏的特征导致气井需要多年才能进入拟稳定流动阶段,可用于做递减分析的生产数据通常包含或仅有处于不稳定流动阶段的生产数据,不同产层渗透率的差异可能引起层间不同流动阶段共存,导致拟合求得的递减指数异常(b>1),预测的储量过于乐观。总结了致密砂岩气藏的主要特征,阐述了递减参数选择存在的误区,引入改进的Arps递减参数取值新方法。利用一口有代表性的老井的历史生产数据,展示了如何利用新方法选择递减参数及最终预测效果。新方法预测的生产动态与真实生产情况高度吻合,预测储量与真实值的相对误差仅-2.97%。研究显示,改进的递减参数取值方法能较好地利用早期的生产数据,有效降低不稳定流动阶段生产数据对合理递减参数取值的影响,从而有效提高了致密砂岩气井的储量预测的可靠性。

It would take years for tight sandstone gas reservoir to reach pseudo steady flow phase due to its own features. As a re- suh, the production data available for decline analysis often contains or belongs to the data obtained at unsteady flow phase. The co- existence of different flow phases between layers caused by permeability variety of different layers can lead to abnormal decline in- dex （b〉l） obtained by fitting, which furthermore may lead to overestimated reserve forecast. Based on the main features of tight sandstone gas reservoir, this paper first described the inappropriate practices to choose decline parameters, then brought in the im- proved method of Arps for decline parameters determination, and further more showed the way to choose decline parameters and fi- nal forecast effects by using historical production data of a typical old well. The predicted production performance using new meth- od is quite consistent with the actual production performance and the relative error is only -2.97 %. The improved method can ana- lyze the early-time production data and effectively dilute the influence of transient flow data on the determination of reasonable de- cline parameters, and furthermore improve the reliability of reserve forecast of tight sandstone gas wells.