Chinese tight oil is mainly distributed in continental petroliferous basins of the Mesozoic to Cenozoic

where tight sandstone oil or tight carbonate oil reservoirs are distributed in large areas and are interlayered with or in contact with lacustrine petroleum source rocks.Recently

great progress has been made in continental tight oil exploration and development.By the end of 2018

an annual production capacity of 3.155 million tons was built for Chinese continental tight oil

and its production rate reached 1.05 million tons in 2018.Lacustrine organic-rich shale in China serves as the main hydrocarbon source rocks of the Chinese continental tight oil.Most of the shale was deposited in fresh

brackish-to-saline water environments with a thickness of tens of to several hundred meters

having a total organic carbon (TOC) content of 0.4% to 16% and a vitrinite reflectance (R

o

) of 0.5% to 1.3%. Appropriate volcanism

low sedimentation rate

anoxic and reducing environment

transgression

and stratification of water body are dominant factors controlling the quality of organic-rich shales.Chinese continental tight oil reservoirs include tight sandstone

tight carbonate rock

tight peperite

and tight tuffite

featuring strong heterogeneity and poor physical properties.Their overlying matrix permeability tends to be less than or equal to 0.1×10

-3

μm

2

.Nano-scale pore thoats

complex in structure and with a diameter ranging between 40 nm and 900 nm

are dominant in the reservoir space.Their pressure coefficient varies from 0.7 to 1.8

indicating the coexistence of overpressure and pressure deficiency.Their acquifer energy and oil property vary greatly

with an oil density of 0.75 g/cm

3

to 0.92 g/cm

3

.The continental tight oil in place and technically recoverable resources in China are 178.20×10

8

t and 17.65×10

8

t respectively

mainly distributed in the Ordos Basin

Bohai Bay Basin

Songliao Basin

Junggar Basin and Qaidam Basin.In conclusion

we put forward the concept of "sweet spot zone (section)"

which tends to develop in local

low amplitude structures in a wide

gentle structure setting.A sweet spot zone refers to a tight oil-rich area with commercial productivity within the distribution area of mature high-quality source rocks; while a sweet spot section refers to a high productivity interval of tight oil with commercial value through artificial stimulation

located in the black shale section intercalated by tight reservoir layers.The source rock quality and the type of source-reservoir configuration serve to control the lateral distribution of the sweet spot zones.Sweet spot zone (section) evaluation methods

including resource assessment technique

logging identification of the "six properties"

high-resolution 3D seismic imaging

horizontal well production from well pads

and artificial reservoir alternation

may facilitate the efficient development of tight oil.