The Mechanism of Secondary Pore of the Beach-Bar Sandstones and Prediction of Favorable Regions in the Upper Es4 of the Palaeogene, Boxing Sag

摘要

Based on the date analysis of casting lamella, scan electron microscope and reservoir pressure, the mechanism of secondary pore of the beach-bar sandstones are researched in the upper Es4 of the Palaeogene in Boxing Sag. These secondary pores mainly include intergranular pore, intragranular pore, moldic pore, oversized pore and a few fracture pores. The selective dissolution is the primary cause which produced the secondary pore during the diagenetic process. The upcurrent of deep level promote the migration of pore water and create the condition for forming secondary pore. The aluminosilicate and the carbonate are dissolved by CO2 and the organic acid, which form the large-scale effective secondary pore in the area. The transformation of day mineral also contributes to the forming of secondary pore. The beach-bar sandstone can be divided into four types of diagenetic facies. The area controlled by unstable clastic dissolution fades have massive secondary pore and the reservoir quality is best in the studied area. The sandstones with carbonate cementation fades and compaction-dissolution fades have the lesser porosity.