Abstract:

Taking  the  layer Chang  (4+5) and  the  layer Chang 6 of Yanchang Formation  in Hujianshan area of Ordos basin  for
example,  the authors analyze  the oil-transporting petrophysical  lowest  limit values  in sandstone conducting system and  their
affections  to  the oil migration and accumulation. These values are  related  to  the displacement pressure. When  the oil-driving
force is similar, the higher the permeability and porosity of sandstones are, the easier the oil filling in them. In the same area, for the similar depth and similar layer, there is a lowest value of sandstones
,
 permeability and porosity at which oil can fill in them.
Only when  the permeability and porosity of sandstones are higher  than  their  lowest  limit values,  the oil  filling can be possible.
Otherwise,  the oil can
,
t do  so because of  the higher  resistance  force. The displacement pressure  is positively correlated  to
permeability and porosity properties of sandstones. Because the permeability and porosity of sandstones decrease while the depth
increases, when the depth increases greatly, the permeability and porosity lowest limit values of effective transporting properties of
sandstones would decrease by depth increasing. Generally, the sandstones have strong anisotropism both in vertical and horizontal
directions. Under the similar dynamic conditions, there are different lowest limit values of porosity and permeability  in different
sandstones and different places of the same sandstone layer, and therefore, the oil accumulation degree would be different. For the
Hujianshan area, the formation depth varies mainly from 1 700 m to 2 400 m. Correspondingly, the lowest limits of porosity and
permearbility of sandstones change from 6% to 3.2% and from 0.062×10-3
μm2
 to 0.019×10-3
μm2
, respectively.

Key words: permeability, porosity, lower limit values, conducting system, Ordos basin