Porosity evolution of reservoirs is a key and difficult point of the study on hydrocarbon accumulation mechanism.But the present research methods of "porosity inversion and back stripping" have some flaws

including equating thin section porosity with porosity

attributing the porosity loss by compaction to early diagenetic stage

and neglecting rock bulk volume's reduction in the compacting process.In this study

compaction was corrected in every stage of diage-nesis according to the normal compaction curve.Equation of porosity variation through history is derived

accounting for the porosity loss through compaction and cementation

and also porosity increase by corrosion

also taking into account of rock bulk volume variation in every stage of diagenesis.A case study on Chang 7 and Chang 6

3

tight oil reservoir of the southwest Ordos Basin was carried out

integrating the diagenetic facies of the research area and the derived formula.We reconstructed the porosity evolution from inversion and back stripping under the constraint of diagenetic sequences

and built five porosity evolution pattern and porosity evolution curve by different methods.If compaction is not corrected and rock bulk volume change is not considered

large error of the recovered porosity exist and it may be up to 13.8%.