Petrology and diagenesis of the low permeable reservoir rocks from the Paleogene Shahejie Formation in central Bonan Oil Field, Shandong

The Petrology and diagenesis of the low permeable reservoirs from the Paleogene Shahejie Formation in central Bonan Oil Field, Shandong are examined on the basis of drilling cores, thin sections, microprobe (analysis), scanning electron microscopy, cathodoluminescence and X-ray diffraction analysis. The reservoir rocks consist mostly of lithic arkose. The dissolution is believed to be a dominantly constructive diagenesis, whereas the compaction, filling and cementation of authigenic minerals are considered as a dominantly destructive diagenesis. The diagenesis may be ascribed to the A substage of the late diagenetic stages. The highly dissolution during the late diagenetic stages was responsible for the formation of the higher porosity of the reservoir rocks. The genetic mechanisms of the low porosity of the reservoir rocks include the compaction, filling and cementation of authigenic minerals during the late diagenetic stages. The isolated and disconnected interparticle porosities caused by the dissolution permitted the low permeable microthroats to be developed. The good porosity associations consist of interparticle porosity-primary interparticle porosity-intraparticle cracks. The distribution of the favourable reservoir rocks tends to be governed by sandstone distribution, structural arrangement and diagenesis.