Controlling factors of the clastic reservoirs in the Upper Shihezi Formation, southern Kongdian, Dagang Oil Field

The clastic reservoirs in the Upper Shihezi Formation, southern Kongdian, Dagang Oil Field are expected to be the favourable area for the Palaeozoic petroleum exploration. The present paper deals with the lithology and physical properties of the clastic reservoirs and their controlling factors on the basis of cores and cast thin sections, SEM, X-ray diffractional patterns and vitrinite reflectance. The clastic reservoirs in the Upper Shihezi Formation are made up of low-porosity and low-permeability reservoirs. There a positive correlation between the porosity and permeability. The clastic reservoirs are well connected, and assigned to the porosity-type reservoirs. The porosity type is dominated by secondary intergranular solution openings. During the late diagenesis, the dissolution of lithoclastics, interstitial material, feldspar grains and kaolinite brought about abundant secondary pores, and resulted in the improvement of the porosity and permeability of the clastic reservoirs. The major controlling factors include sedimentary facies, compaction, cementation and dissolution.