Abstract: The low-ultra low permeability sandstones in the glutentite reservoirs play an important role in the oil migration and
accumulation. To understand the micro-pore and throat distribution and contribution of different sizes of pores and throats to physical
property of tight sandstones with different permeability grades, a case study was conducted in the fan delta glutenite reservoirs of the
steep slope zone of the Shijiutuo uplift by using constant-rate mercury injection technique. Results show that low-ultra low permeability
sandstones are characterized by medium pore size, small throat radius and large pore throat ratio compared with conventional
sandstones. Permeability is affected by pore and throat radius obviously, and the number and distribution of the throat with large radius
are key to affect the seepage capacity of reservoir. The pore-controlled mercury entry zone is the most effective and important space for
fluid flow. The higher the permeability is, the larger the throat radius of the pore master zone is. In the pore-throat transition mercury
zone, mercury is mainly combined by pore and throat. With the decreasing of throat radius, fine throat gradually becomes the main
space for fluid storage and flow. The contribution of permeability in the main control area is also very low. The micro-and fine-throat are
throat radius. With the increasing of permeability, the critical throat radius of the permeability of the low-ultra low permeability
sandstones increases from 1-2 μm to 3-4 μm. Therefore, based on the constant-rate mercury injection technique, quantitative
characterization of micro-pore and throat of low and ultra low permeability sandstones fills the research gap in the Bohai area. This
would be helpful to the realization of comprehensive and accurate evaluation of such reservoirs.

Key words: low-ultra low permeability sandstone, glutenite, constant velocity mercury injection, micro pore throat characteristics