Study On Pore Structure And Reservoir Physical Properties In Shale Of Chang 7^th Of Yanchang Formation,Ordos Basin

This article selects the shale of Chang 7th of Yanchang formation in Ordos Basin as the research object.Through field outcrop observation,core observation,thin section observation,rock slice,X-diffraction and other experiments,the feature of the sample in the research area were learned,and clarified the macroscopic and microscopic characteristics of shale reservoir in the study area.Based on the petrological characteristics of the sample,a rock types scheme suitable for the Chang7^th shale in the Ordos Basin was established.The organic matter was used as the standard,and the carbon,low carbon,Medium carbon,high carbon,carbon-rich was divided by 0.5,1,2,3,and 4 of TOC,and based on rock mineral components,such as clay minerals,silty and carbonate minerals,divide into 12 rock types and mixed shale.At the same time,the structural types of rock are introduced in the partitioning method.Finally,the samples in the study area are mainly divided into three sub-phases and 9 lithofacies.Based on the investigation of papers of pores of shale reservoirs at home and abroad,the pore types of the main development were clarified by scanning electron microscopy and nitrogen adsorption experiments.According to the genesis of pore development,they can be divided into:inorganic pores,organic pores and micro-cracks.Inorganic pores refer to pores that are mainly developed in the interior or at intervals of mineral or inorganic components,and diagenesis and tectonic effects have a greater influence on such pores.The inorganic pores can be further divided into primary pores and secondary pores.Primary porosity refers to the pores formed by rock during diagenesis or deposition.The primary pores can be further divided into intra-crystal?particle?,inter-crystal?particle?,the inter-crystal crack.Secondary pores refer to the pores formed by the dissolution of non-silicate components?mainly carbonate components?in diagenesis,and can be divided into intra-crystal?particle?solution pores and solution pores between crystal?particle?.This type of pore is mainly controlled by the influence of mineral components and temperature and pressure.Organic pores can be divided into organic hydrocarbon evolution pores and organic matter margin pores according to their genesis.The organic hydrocarbon evolution pores can be further divided into organic bubble-like pores,flaky pores and honeycomb pores according to the occurrence.According to the cause,it can be called the vent,the oil hole and the stomata.The degree of development of such pores is mainly related to the maturity of organic matter.When the maturity of organic matter is higher,the dense pore group is more likely to appear and the state of the pore group is present.The edge of the organic matter is mainly the shrinkage of the organic matter formed by the reduction of the volume of the organic matter.Micro-cracks are mainly composed of structural joints.In the study of pore structure,through the experimental analysis,the types of pore development in the sample were statistically analyzed.It was found that the intergranular pores in the sample accounted for the highest frequency,reaching 29.55%of the total proportion.The organic pores,crystal gaps,and intragranular pores reached 20%,19.13%,and 15.37%of the total pore volume.According to the nitrogen adsorption experiment,the adsorption-desorption curves of two types of hysteresis loops are obtained.The main pore morphology is parallel plate-like pores,ink bottle-like pores and uniform pores of straight or cylindrical shape.Based on the combination of various research data,the physical properties of the samples were further studied,and the control factors of the Chang 7^th reservoir properties were analyzed.According to the experimental data,the effects of the structure of pore,sedimentation,diagenesis,lithology,organic matter and mineral composition on the physical properties of the Chang 7 reservoir were analyzed.The abundance and maturity of organic matter controlled the development and evolution of organic pores.