Quantitative evaluation and prediction of diagenesis facies with low porosity and permeability sandstone in central Sichuan: A case study of 2nd member of Xujiahe Formation in Suining-Pengxi area

The sandstone reservoir in 2nd member of the Upper Triassic Xujiahe Formation in central Sichuan Basin is the prominent representative of China's low permeability tight sandstone. Diagenesis has an important influence on sandstone's compaction. Based on the cast- slice, cathodoluminescence, electron microprobe analysis, SEM and other means of experimental analysis, the authors analyzed different types of diagenesis and features and divided diagenetic facies into six kinds according to the dominant or characteristic diagenesis that controls the porosity evolution. Quantitative evaluation of the intensities of different diagenetic activities was made, and different diagenetic facies types were distinguished by introducing such indexes as the compaction rate, the cementation rate, the microporosity and diagenetic coefficient. The porosity and permeability—diagenetic coefficient interpretation model was tentatively established with the exploratory application of robust regression method. Un-coring well's parameters were explained by the diagenetic coefficient interpretation model, the diagenetic coefficient contour map was drawn, and the regional distribution of favorable diagenetic facies was predicated. The reservoir (> 6% porosity) diagenetic coefficient contour map was drawn, and the favorable diagenetic facies- favorable reservoir development area was delineated. All these results obtained by the authors provide a possibility for realizing quantitative evaluation of diagenesis and diagenetic facies, and the rapid prediction of diagenetic facies provides a basis for the screening of favorable reservoir development areas. These achievements have guiding significance for the exploration and development of tight sandstone gas reservoirs.