Effect of Quartz Overgrowth on Sandstone Densification: Typical Example from the Shanxi Formation in the Zhidan Exploration Area, Ordos Basin

The Upper Paleozoic natural gas exploration in the Zhidan exploration area of Ordos Basin has made a breakthrough, and the Shanxi Formation is the main gas reservoir. The Shanxi Formation reservoir in eastern Ordos Basin, extremely poor in physical property, belongs to a typical tight sandstone. The core samples measure a minimum porosity of 1.23%, a maximum porosity of 13.49%, and an average of 5.4%. In this paper, the development process of tight sandstone in this area is explored through the observation of core slices, temperature measurement of inclusions, restoration of burial history, and restoration of thermal history. It can be reserved that quartz overgrowth edge developed very well in studying area, and large amounts of fluid inclusions exist in quartz overgrowth edge. In I phase, the palaeogeothermal in the fluid inclusion was between 80℃ to 120℃.When it came to II phase and III phase the range of palaeogeothermal during the development of quartz overgrowth edges were 130℃–170℃. It can be inferred that in I phase the quartz overgrowth edge began to developed in early diagenetic stage B, and developed continuously in late diagenetic stage A. II phase and III phase the quartz overgrowth edge developed in late diagenetic stage A, and kept developing in late diagenetic stage B and C. In the early diagenetic stage A, the reduction of porosity was mainly results of mechanical compaction; and in the late diagenetic stage A, it was mainly leaded by siliceous cementation which was produced by the development of quartz overgrowth edge. The two kinds of destructive diagenesis lead to the tightness of sandstone in the study area.