THE GEOLOGICAL CHARACTERS OF THE TIGHT OIL/GAS RESERVOIRS IN DAANZHAI SECTON NORTHERN SICHUAN AND THE EXPLORATION TECHNIQUE FOR IT

Coquina is the main reservoir rocks in Daanzhai Section of northern Sichuan,but its porosity, permeability and pore geometry are quite poor. The secondary dissolution pores, caves and fractures constitute most of the space for the storage and accumulation of oil/gas. The main type of the facies of oil/gas pools is shelly bank with nonstratified and inhomogeneous characters. The shelly bank facies controls the enriched oil/gas zones. The local structures and fractures formed in the later stage of the tectonic movement did not rework much the shelly bank oil/gas pools and did not significantly redistributed the previously formed oil and gas pools. Therefore,the exploration of commecial oil/gas pools in the section of northern Sichuan should be focused on the main body of the shelly bank located in the interior zone of shallow water lacustrine facies surrounding the sub deep-deep water la-custrine facies of the oil-generative depression.