Characteristics of Pore Evolution and Its Controls of Lower Cretaceous Reservoir in Ying’er Depression, Jiudong Basin

Key words: 
• pore evolution /
• lowporosity and lowpermeability reservoir

Abstract: The reservoirs of Ying’er depression in Jiudong basin are characterized by low porosity and low permeability. The general poor physical properties of the reservoirs strictly restrict the exploration in this area. Based on analyses of thin sections, casting thin sections and fluorescence thin sections, Xray diffraction analyses, SEM observations and mercury porosimetry measurements of the reservoir sandstones, this research shows that the main pore types are the intergranular dissolved pore and intragranular dissolved pore of feldspar, siliceous debris, quartz and carbonate cements. Two secondary pore zones are developed in the lower member of Xiagou formation and the top part of Chijinbao formation. Sandstones in the study area are characterized by poor sorting, poor roundness and low mineralogical maturity. These are the characteristics of fast accumulation and closure to provenance of the sediments. Mechanical compaction is the main factor in making the properties of reservoirs poor. Clay minerals and carbonate cements block pores. Cements fill in the pore space and destroy the reservoir property, meanwhile, they provide space for dissolution in the later stage, secondary pore is widely developed because of dissolution of minerals caused by acidic water that released by hydrocarbon generation process and diagenesis processes of clay minerals. It's the main factor that improves the reservoir property in the deep layers of the basin.