Abstract:

Studying the main controlling factors of the formation of high-quality sandstone reservoirs of the Upper Paleozoic in Dongpu Depression can provide a basis for predicting high-quality reservoirs. This paper focuses on the Q3 well. Through comprehensive analyses of core observations, casting thin section, XRD, nuclear magnetic resonance cryoporometry and TIB-field emission scanning electron microscopy, the characteristics and controlling factors of the Permian reservoir in Dongpu Depression were studied. The results show that the Upper Paleozoic sandstone in Dongpu Depression is dominated by lithic feldspar and feldspar sandstones, the porosity is 0.2%-12.8% and the permeability is 0.0016-5.7 mD, which belongs to the ultra-low porosity reservoir. The residual intergranular pore, intragranular dissolution pore, carbonate mineral intergranular pore and clay mineral intergranular pore are the main pore types. Secondary pores were mainly formed by the dissolution of feldspar particles and cuttings (including tuff), which are more common in the reservoirs of P2sh Formation and P1x Formation. The high-quality reservoir is controlled by sedimentary facies, lithology, and diagenesis. The sandstone of P2sh Formation belongs to the inland river facies, the river bed is widely distributed and the sand body is developed. It is one of the most favorable reservoir system in the Upper Paleozoic of Dongpu Depression. The dissolution of feldspar is the main controlling factor of the formation of high-quality reservoir of P2sh Formation. The P1x Formation belongs to delta deposition, which was caused by volcanic activity during the sedimentary period, resulting in a large amount of tuff deposition. The kaolinite intergranular pores formed by erosion of tuff is an important mechanism for the formation of this reservoir. The main delta deposits in P1s Formation are also the main coal forming period. The acid fluid of coal system leads to the dissolution, but the large secondary increase in quartz makes the sandstone dense.

Key words: Dongpu Depression, Upper-Paleozoic, dominant factors, reservoir characteristics, diagenesis