Based on drilling

mud logging

wireline logging

production test results

thin section observation and laboratory data

this paper focuses on a study on accumulation conditions

source rock qualities

migration-accumulation conditions of the Chang-7 tight oil reservoirs in Huaqing area

Erdos Basin.A tight oil pooling model is also established.The result shows that the reservoirs are mainly feldspar lithic sandstones with an average porosity of 7.4%

and an average permeability of 0.134×10

-3

μm

2

.The reservoirs are also found to contain largely secondary dissolved nanopores (accounting for 70.6% of the total surface porosity) with radius mostly less than 1 μm.The best source rock of Chang-7 occurs in the third interval of Chang-7.It has an average TOC of 8.99%

obviously greater than that of its second (2.17%) and the first (1.12%) intervals.Its thickness ranges between 28 m and 36 m

while the total thickness of the first and the second intervals is between 35 m and 55 m.It has Ro values between 1.02% and 1.2%

clearly a type I kerogen and within the peak stage of hydrocarbon generation (the hydrocarbon generation capacity is up to 600×10

4

t/km

2

).The migration pathway in Chang-7 is a three dimensional network carrier system consisting of horizontal fractures

oblique crossing fractures and sandbodies.The oblique crossing fractures on the source-reservoir interface are considered to be the primary pathways for the initially expulsed hydrocarbons.The migration is driven by an overpressure in the range from 15 MPa to 22 MPa caused by hydrocarbon generation.The tight oil reservoirs in Chang-7 include lithologic thinning-out type

lenticular type and diagenetic trap type and they are large in number and are laterally connected and vertically superposed

thus being quasi-continuous reservoirs.The source rock in the third interval of Chang-7 and the reservoirs in its first and second intervals constitute a lower-generation and upper-storage assemblage

and the source rocks and reservoirs within the first and second intervals of the Chang-7 form inner-source alternating assemblages.The two types of assemblages constitute a quasi-continuous type of reservoir-forming model with two-source hydrocarbon supply.