Statistics of gas in place

gas-bearing area and reservoiring period of over 60 large and medium gas fields in China show that their accumulation efficiencies vary greatly.China's large and medium gas fields can be classified into 3 types

including high

moderate and low efficiency gas fields

according to their accumulation efficiencies.Gas accumulation efficiency of high efficiency gas fields is over 100?10

6

m

3

/(Ma·km

2

)

that of moderate efficiency gas fields is in the range of 10?10

6

-100?10

6

m

3

/(Ma·km

2

)

and that of low efficiency gas fields is below 10?10

6

m

3

/(Ma·km

2

).The gas accumulation efficiencies of China's large and medium gas fields are mainly controlled by gas generating intensity of source rocks

gas delivery rate

sealing(ability)and timing of gas reservoiring period.The larger gas generating intensity

higher gas delivery speed

larger comprehensive sealing index of cap rocks(CSI)

and later gas reservoiring period would lead to higher gas accumulation efficiency

and vice versa.