At present

taking a single well as an evaluation unit is a common and accurate method to estimate SEC reserves of shale gas. With the further development of the gas fields

the single well production fluctuates greatly

which can not better reflect the development performance of the gas reservoir. In order to further improve the accuracy of the estimation

Pingqiao South Block of Nanchuan Gas Field is divided into four zones

namely Zone Ⅰ

Zone Ⅱ

Zone Ⅲ and Zone Ⅳ

by the study of regional production rules and combining with geological characteristics based on the single well estimation. The yield normalization method is used to establish the typical curve of each zone

and then the theoretical yield model of this block is established by the dual medium model

so as to meet the harmonic decline. Finally

the evaluation models of different zones are established. Zone Ⅰ directly enters into the harmonic decline with an initial decline rate of 56.5 %; Zone Ⅱ enters into the harmonic decline after 23 months of stable production with an initial decline rate of 52.2 %; Zone Ⅲ enters into the harmonic decline after 13 months of stable production with an initial decline rate of 60.7 %; Zone Ⅳ directly entered into the harmonic decline with an initial decline rate of 59.5 %. The final estimation results are compared with those of foreign countries

and the error is within 6 %

which shows that the estimation of the SEC reserves for each unit of shale gas in Pingqiao South Block in the middle and later period of development has certain adaptability.