The quality parameters of dolomite and tight sandstone reservoirs are a randomly distributed continuum.Their pore structures and physical parameters are complex and changeable

and are thus hard to be characterized.With the help of techniques such as thin section casting

mercury injection

nuclear magnetic resonance(NMR)

and measurements of porosity and permeability

and a large number of data for natural gas exploration and development

we focused the study on analyzing and comparing the macroscopic and microscopic characteristics of the parameters of the reservoir quality.Results show that the quality parameters of dolomite and tight sandstone reservoirs are normally distributed in a pyramidal data structure.The proportion of conventional reservoirs is generally ranging from 15% to 20%

which are the "sweet spots" of the sandstone or tight dolomite reservoirs.The microscopic pores are well developed with good pore-throat connectivity and uniform distribution in the tight sandstone reservoirs.The reservoir porosity and permeability are of good relationship

showing relatively high porosity and low permeability.The tight dolomite reservoirs

however

are characterized by unfavorable factors including poor pore-throat connectivity and poor relationship of porosity and permeability

while having certain favorable factors of its kind including relatively high permeability

low irreducible water saturation

low displacement pressure

and better development of fracture networks.These favorable factors keep the natural gases flow well in tight dolomite reservoirs

indicating great potentials for the exploration and development of hydrocarbons.Carbonate deposits are well developed in China

so the exploration of tight dolomite gas reservoirs and study on their accumulation conditions should be strengthened.