Huanghua depression in the Bohai Bay Basin has gone through three stages of structural-lithological reservoir exploration

lithological rese

rvoir exploration in slope zones

and lithological reservoir exploration in deep subsag zones. The cumulative proven petroleum geological reserves in Huanghua depression exceed 1.3×10

8

t

and more than 50 % of conventional petroleum reserves have been proved

indicating that the whole Huanghua depression has entered a highly mature exploration stage. By contrast

there are tight oil and gas of low exploration degree and large remaining oil and gas resources in Bohai Bay Basin

which is an important exploration field for Dagang oilfield to increase reserves and production in the future. Based on the data of drilling

geophysical survey

and experimental test in recent years

the paper systematically analyzes the favorable hydrocarbon accumulation conditions

accumulation periods

accumulation model

and resource potential of tight oil and gas in Huanghua depression. The research results show as follows. (1)Huanghua depression possesses favorable conditions for the accumulation of tight oil and gas. The fault activity and thermal subsidence that have a controlling effect on the basin and depressions have led to the formation of vast reservoir spaces in deep layers of the basin

providing a favorable tectonic setting for the input of sedimentary provenance. During the depositional periods of the Kongdian Formation

Shahejie Formation

and Dongying Formation

sand bodies were widely distributed. The four main source rock formations

i.e.

Member 2 of Kongdian Formation (E

2

k

2

)

Member 3 of Shahejie Formation (E

3

s

3

)

Member 1 of Shahejie Formation (E

3

s

1

)

and Member 3 of Dongying Formation (E

3

d

3

)

are widely distributed in Huangye depression

and have high hydrocarbon generation intensity and superior hydrocarbon supply conditions

which can provide an important resource foundation for the enrichment of tight oil and gas. Strong dissolution leads to the development of dissolution pores in tight oil and gas reservoirs

thus

improving the reservoir conditions. There are three types of source-reservoir assemblage patterns

i.e.

lower generation and upper accumulation pattern

three-dimensional filling pattern

and lateral hydrocarbon migration and accumulation pattern

demontrating excellent conditions for configuration of source rocks and reservoirs. (2)There are two main accumulation periods of tight oil and gas in Huanghua depression

i.e.

sedimentary period from Shahejie Formation to Dongying Formation and sedimentary period from Minghuazhen Formation to the present. The tight oil and gas reservoirs in Huanghua depression are mainly developed in the deep subsag zone and the lower step fault zone around the sag

with the characteristics of "source-reservoir coupling and continuous accumulation". (3)Huanghua depression is rich in tight oil and gas resources

including the tight oil resources of 2.82×10

8

t

1.17× 10

8

t and 5.92×10

8

t in E

2

k

2

of Cangdong sag

Dongying Formation and Shahejie Formation of Qikou sag

respectively

and also the tight gas resources of 2 875×10

8

m

3

in Shahejie Formation of Qikou sag. Based on the comprehensive evaluation and analysis of petroleum geological conditions

remaining oil and gas volume

and exploration practice of different layers of petroleum systems in each area

it is determined that the E

2

k

2

of Cangdong deep subsag zone

E

2

k

2

of Changzhuang subsag

and Dongying Formation of Qikou deep subsag zone are favorable new areas for exploration of tight oil

and the E

3

s

3

of Banqiao subsag and southwestern edge of Qikou sag are favorable new areas for exploration of tight gas. The new understandings of geology and resource potential resulted from the breakthrough in tight oil and gas exploration can provide technological support for the subsequent sustained and highly efficient exploration in Huanghua depression.