Characterization And Genesis Of Micro-Pores And Micro-Fractures In Tight Clastic Rock Reservoir Of Longfengshan Sub-Sag In Changling Fault Depression

With the progress of oil and gas exploration and development and the continuous improvement of technology,unconventional oil and gas resources are getting more and more attention.Tight clastic rock reservoirs usually have the characteristics of ultra-low porosity,ultra-low permeability,small pore throat,complex structure,and strong heterogeneity,making it difficult for tight oil and gas exploration and development,Accurately and quantitatively characterize the micro-pore structure of tight reservoirs and characterize the micro-pore-fracture network of the reservoir are the key to studying unconventional oil and gas geology.This paper takes the tight clastic reservoirs of the Longfengshan sub-sag in the Changling Fault Depression of the Songliao Basin as the research object,comprehensively using polarized light microscope,scanning electron microscope,X-diffraction,image analysis,high pressure mercury injection,low temperature nitrogen adsorption,nuclear magnetic resonance,micron CT and other conventional and unconventional reservoir research methods are used to quantitatively characterize the microscopic pore-fracture structure of tight clastic rock reservoirs in the Yingcheng Formation in the study area.Combined with water-rock simulation experiments and paleo-pressure recovery of inclusions,the genetic mechanisms of different types of pores and fractures in the tight clastic reservoirs of the Yingcheng Formation in the study area were discussed,and favorable target areas were predicted.The storage space types of tight clastic reservoir in Yingcheng Formation in the study area is mainly including secondary dissolution pores,residual intergranular pores and micro-fractures.Among them,the secondary dissolution pores accounted for about 60.3%,mainly the dissolution pores in the volcanic rock cuttings,and the feldspar and quartz particles have fewer dissolution pores.The intergranular dissolution pores are less developed,including laumontite cement and calcareous cement dissolution pores.The remaining primary pores are mainly Concentrated in Well B202,Well B203 and Well B204.Microcracks mainly include grain-edge fractures,transgranular fractures and intragranular fractures.The capillary pressure curve of the tight clastic reservoir in Yingcheng Formation in the study area is mainly divided into two forms,corresponding to the two-peak and double-peak pore throat distribution characteristics.There is an obvious correlation between high-pressure mercury injection parameters and porosity.The higher the porosity,the more uniform the pore throat distribution,the worse the sorting,and the stronger the tortuosity of the pores.The pore throat shape is dominated by parallel plate-shaped slit holes,some of which are narrow-necked wide-body"ink bottle"holes.The microscopic pore throat structure of the slit type is better than that of the"ink bottle"type.The microscopic pores are in the form of"honeycomb"type,and the macropores are composed of numerous small pores.The movable fluid saturation of the samples is low,with an average of 30.15%.The fluid mobility of the slit hole is stronger than that of the"ink bottle"hole.The full pore size distribution shows that the full pore size distribution of the tight clastic reservoirs in the Yingcheng Formation is bimodal.Nano-scale pore throats account for about 91.58%of the storage space,of which mesopores account for about 49.81%.Nano-scale pore throats are the main storage space for tight gas.The average micro-crack opening is 2.8μm,and the average areal density is 1.0 mm/mm~2.Pore-lining chlorite plays a vital role in the preservation of primary pores,Pore-lining chlorite can slow down compaction and inhibit quartz secondary growth and carbonate cementation,so that the primary pores can be preserved;water-rock simulation experiments confirmed that volcanic rocks debris are easy to form dissolution pores and are the main contributor to secondary pores in the study area;the Raman displacement technology of methane inclusions confirms the existence of hydrocarbon generation pressurization,and overpressure controls the development of micro-fractures,which is one of the main controlling factors for high-quality reservoirs.