The microstructure of pores strongly influences fluid
mobility
in tight sandstone reservoirs. The impacts of the pore–throat
structure on fluid mobility are restricted due to the limitations
of existing methods for determining pore–throat structures.
Therefore, the methods utilized to obtain more comprehensive and accurate
pore–throat information need to be further discussed by combining
multiple experiments. In this research, eight samples were selected
from the Upper Triassic Yanchang Formation in the Ordos Basin to investigate
the microstructure and its impacts on fluid mobility by means of nuclear
magnetic resonance (NMR), rate-controlled porosimetry (RCP), scanning
electron microscopy, and thin sections. The throat radii in the throat,
pore–throat, and pore areas were studied by combining NMR and
RCP with an improved method. The throat radius and pore–throat
volume affect the movable fluid from connectivity and movable ratio,
respectively. The throat and pore–throat (pore) areas belong
to unrelated movable fluid networks. Each area contains intragranular
and intergranular spaces. Irregularly shaped pores commonly occur
in the intragranular space, with strong connectivity. The pores with
regular shape in the intergranular space connect a small amount of
throat, and a large number of clay minerals divide the space into
small throats. Clay minerals reduce fluid mobility by increasing the
thickness of the water film in the throat. Therefore, fluid mobility
in the intragranular space is greater than that in the intergranular
space from the perspective of water film thickness and movable probability
in the same area. This research improves the accuracy of the combined
method of NMR and RCP and clarifies the distribution mechanism of
movable fluids in different spaces.
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