Abstract:

Based on outcrop/core, thin-section, cathodoluminescence, scanning electron microscope, X-ray diffractions, physical properties and carbonate contents, we studied the characteristic of petrology and diagenesis of Laiyang Formation in Laiyang sag. It shows that feldspar sandstone is mainly developed in the eastern Laiyang sag, while litharenite in the western Laiyang sag. The Laiyang Formation contains variety of plastic lithics with low compositional mature and medium textural mature. Laiyang Formation is tightly compacted, and rich in pressure solution and cementation. The characteristic of diagenesis in the eastern Laiyang sag is strong cementation, while weak compaction, and carbonate cement is the major cement which reduced the porosity. In the western Laiyang sag, the sandstone diagenesis is dominated by compaction, and the presence of pore lining chlorite cement can restrain compaction and is beneficial to preserve primary porosity. Secondary porosity is the most important reservoir space in the Laiyang Formation, physical properties of sandstone reservoirs can be improved by dissolution, especially, of feldspar during the middle period of diagenesis. Secondary pores are vertically developed in Longwangzhuang (K₁llw) and Shuinan (K₁ls) Members, and diagenesis reaches A-period of middle diagenesis stage. Secondary porosity developed by dissolution is one of the main porosity-type of this period. These zones are the favorable reservoirs area.

Key words: reservoirs, diagenesis, pore evolution, Laiyang Formation, Laiyang sag, Jiaolai basin