页岩气产量幂律指数递减分析

摘要

Shale gas reservoir is a kind of unconventional gas reservoir characteristic by extra-low porosity and extremely low permeability,as well as adsorption-desorption and diffusion,etc. There is a large error when analyzing a shale gas well with conventional production decline methods. Consequently,given that Arps production decline method can’t use the early production data for prediction,the power law exponential decline method was presented,the power law exponential decline type curves with different decline exponent were drawn based on the mathematical model,and the influence of decline exponent on production decline law was analyzed. In addition,the production data of a shale gas well in Sichuan Basin was analyzed to show that the results of power law exponential decline method and Topaze software were almost the same,while hyperbolic decline method would get extremely high reserves. The results suggest that the early production data of shale gas well displays the feature of power law exponential decline. The power law exponential decline method can be used to forecast the shale gas production,recoverable resources and decline rate fast. The rate of shale gas well is low,however,it has a large recoverable reserve for a long life time.%页岩气藏属于特低孔、特低渗的非常规天然气藏，且存在吸附-解吸及扩散等特征，采用常规产量递减方法分析页岩气井存在较大误差。针对Arps产量递减方法无法利用气井早期生产数据进行产量预测的不足，引入幂律指数递减分析方法，基于所建立的数学模型绘制不同递减指数下的幂律指数递减典型图版，分析了递减指数对产量递减的影响，并对四川盆地某页岩气井生产数据进行了分析，对比发现幂律指数递减与Topaze预测结果十分吻合，而双曲递减会导致储量估算过高。研究表明：页岩气井早期产量表现出幂律指数递减特征，利用幂律指数递减分析方法可对气井产量、可采储量及递减率进行快速预测；页岩气井单井产量低，但生产周期极长，单井可采储量较大。