Pore Structure Characteristics And Their Influence Factors Of Paleogene Shales In Nanpu Depression

The research on accumulation of shale oil and gas is in its infancy in Nanpu Depression.Its occurrence and exploration potential are still unclear.The study integrated use of basic geological data,focus on the distribution of shale,mineralogy characteristics,microscopic pore characteristics and adsorption characteristics,aiming to guide the future exploration and exploitation of the shale gas.The study was based on the methods and results from the previous research that is related to the shale gas.Abudant data was collected including the data from drilling,well log,logging,stratigraphic,element and mineral.Furthermore,many samples were tested in this study to obtain scientific and convincing information.Numerous experiments were done such as N2 adsorption experiments,methane adsorption experiments,X-RD whole rock identification experiments,ICP-AES,scanning electron microscopy,energy spectrometer.Studies have shown that spatial distribution of Nanpu Depression shale is generally widely distributed and thick.Lithofacies can be divided into three main types with five hypo-types.Certain lithofacies have significant response characteristics in logging curve.Whole rock mineral composition are well comparable to Marellus shale and Haynesville shale.Pore types in this district are organic pore,intergranular pore,intragranular pore and microfracture.Pore structure is complicated,including ink-bottle-like,slit-like and wedge-like pores.Ink-bottle-like pores which are favourable for gas absorption are the main pores.From the view of aperture,Micropores and mesopores are well developed in the region,mesopores provide most of the pore volume,and micropores provide most of the pore surface area.TOC content is the main internal factor to control the volume and surface of nanopores of the Paleogene shale gas reservoir in Nanpu Depression;Quartz and calcite has good correlation with pore volume;Brittle mineral has a positive effect for the construction of the pores,Clay minerals content's contribution to the increase of pore is smaller than expected.Organic acid can make corrosion to unstable minerals such as feldspar and calcite,but the ability to add holes is limited.Tectonism controls the number and distribution of fracture development,which is the main factor in Nanpu 1st,2nd tectonic belt,and Laoyemiao region.The main factor affecting shale methane adsorption capacity is TOC content,but there are other minor factors at the same time.The relationship between maturity and shale adsorption capacity is not clear.Clay mineral such as illite and smectite have positive correlations with adsorption gas in content while carbonate mineral such as calcite have negative correlation with adsorption gas in content.