Characterization Of The Pore Structure Of Mud Shales Of The Luchaogou Formation In The Malang Depression And Evaluation Of Their Oil Content

The mud shale of the Permian Lucaogou Formation in the Malang Sag of the Santanghu Basin is of large thickness and good quality,and has great potential for shale oil resources,but the lithology of the shale oil reservoir of the Lucaogou Formation is complex,the mineral composition and the type of reservoir space are diverse,the state of the shale oil deposit is unclear,and the evaluation of favorable reservoirs is still not in-depth,which restricts the exploration and development of shale oil in the study area.In this thesis,whole-rock X-ray diffraction,polarised light microscopy and field emission scanning electron microscopy,highpressure mercury pressure,nitrogen adsorption and multidimensional nuclear magnetic resonance were used to characterise the mineralogy,organic geochemistry,pore structure and favorable reservoir evaluation of shale oil reservoirs in the Lucaogou Formation of the Malang Sag,with a view to providing a geological basis for the exploration and deployment of onshore shale oil in the Malang Depression.This study is intended to provide a geological basis for the exploration and deployment of onshore shale oil in the Malang Depression.The results of the study showed that:(1)The mud shale of the Lucaogou Formation is mainly composed of longitudinal and carbonate,with contents ranging from 5% to 94% and 2%to 92% respectively,and the clay mineral content is extremely low,with an average value of only 3.2%,rich in volcanic ash material,and the petrographic phases are mainly developed with longitudinal and mixed petrographic phases.(2)Combined with microscopic photographic observations,the lithology of shale oil reservoirs can be classified into four major categories:tuff,dolomite,tuffaceous dolomite and dolomitic tuff;the pore types are intergranular pores,intergranular pores,devitrified pores,soluble pores and organic pores,with devitrified pores,intergranular pores and intergranular pores dominating.(3)High-pressure mercury and nitrogen adsorption and 1D NMR analysis show that pores less than 50 nm provide most of the specific surface area;the morphology of the adsorption-desorption curve is similar to that of Type III,indicating that the pore morphology is mostly semi-closed pores,open pores similar to flat pores and ink bottle-like pores,with micro-pores predominating and some large pores or micro-cracks visible.(4)Analysis based on fractal dimension shows that pores smaller than 50 nm in tuffs and dolomitic tuffs are relatively regular,while pores larger than 50 nm pore size in dolomites and tuffaceous dolomites are relatively regular and have a lower fractal dimension,which is more conducive to providing effective percolation channels;the nitrogen adsorption fractal dimension tends to be closer to 3.0 at lower levels of brittle minerals,indicating that the pore morphology of such reservoirs is relatively complex;by The fractal analysis of SEM images shows that the pore structure of inorganic minerals is more complex than that of organic pores.(5)The analysis of 2D NMR before and after oil washing shows that the proportion of free hydrocarbons is about 20.1% ? 41.9%,and the fluid in the reservoir mostly exists in small pores with relaxation time of 0.01ms?1ms,and some exist in medium to large pores with 1ms?100ms;meanwhile,there is a certain correlation between the state of shale oil fractionation and lithology as well as the clay content contained,with dolomite and The oil saturation of dolomite and tuffaceous dolomite is high,and that of dolomite tuff and tuff is low.The above results suggest that the favorable reservoir lithology of the shale oil in the Lucaogou Formation of the Malang Sag is mainly dolomitic and tuffaceous dolomite.