考虑动态克林伯格系数的煤储层渗透率预测模型

摘要

随着储层压力的降低,克林伯格效应对渗透率的影响越来越大.现有的煤储层渗透率预测模型大都忽略了克林伯格系数的变化,其预测结果与实际生产存在一定的差异,尤其是在低储层压力阶段.本文以体积不变假设为基础,基于火柴棍模型给出在储层压力降低过程中动态克林伯格系数的计算公式,并建立考虑动态克林伯格系数的渗透率预测模型;深入分析在煤储层压力降低过程中,煤储层渗透率和克林伯格系数的变化规律.研究结果表明:随着储层压力的降低,克林伯格系数呈先增大后减小的变化趋势;在相同储层压力下,克林伯格系数随渗透率增加呈指数减小趋势,随温度增加呈线性增大趋势.本文建立的渗透率模型参数简单易获取,预测结果与实际煤储层渗透率变化规律符合性较好,尤其是在低储层压力阶段,能准确预测煤储层渗透率变化.%With pressure decreasing,the Klinkenberg effect plays an more and more important role in permeability of coal reservoirs.While existing prediction models of this issue neglect the change of the Klinkenberg coefficient,which may be responsible for the difference between the prediction results and actual data,especially at low pressure.This paper presents a further demonstration to this issue.Assuming a constant volume and using the Matchstick Model,this work has established a novel prediction model of the permeability and the calculation formula for the process of pressure reduction.We also analyzed the changing rules of the permeability and Kinkenberg coefficient when the pressure in reservoir decreased.The results show that with decreaing reservoir pressure,the Klingberg coefficient shows a trend of increase first and then of decrease.Under a constant reservoir pressure,this coefficient exponentially decreases with increasing permeability but linearly increases with rising temperature.The novel model presented in this paper is simple and its parameters are easy to obtain.The prediction results match well with the actual data from production,especially at the stage of low reservoir pressure.Therefore this model permits to predict the change of permeability in coal reservoirs with a fairly good accuracy.