Abstract: The physical property of Wen 88 Block is low porosity and low permeability with the average porosity at 13.9%，and
the average permeability at 7.4 mD，and its initial formation pressure and temperature is 64.98 MPa and 145 ℃，respectively，
and the pressure coefficient is 1.7∼1.8，so it belongs to abnormal high temperature and high pressure reservoir whose depleted
recovery efficiency is quite low and water injection response is also poor. In order to study the feasibility of reservoir gas
injection，we have carried out gas expansion experiments and long core tests which proved that gas injection can improve the
physical property of crude oil and got displacement efficiency for different gas injection plan. The results of these experiments
show that gas injection can significantly improve physical property of crude oil and have apparent effects on lowering viscosity
and expanding of crude oil. Moreover，the sweep efficiency under the original formation conditions is much better than that
under the present formation conditions. However，the latter can also boost sweep efficiency to a certain extent.

Key words: special low permeability reservoir, abnormal high temperature and pressure, natural gas, displacement experiment, expansion experiment