Genetic Types And Main Controlling Factors Of Microcracks In Tight Oil Reservoirs In Jimusar Sag

The tight sandstone of the Lucaogou Formation in the Jimusaer Sag,Junggar Basin is a typical terrestrial tight oil reservoir,and the micro-fractures in the work area are relatively developed.Growing attentions have been paid to microfractures,the key to the migration and accumulation of source rock and fracturing and exploitation of oil and gas in tight reservoirs,around the world during the last several years.In this dissertation,compact rock samples of the Lucaogou Formation in the Jimusaer Sag,Junggar Basin were selected to study the main controlling factors of microcracks and their effects on reservoir properties in petroleum geology,mineralogy and petrophysics.In this paper,the micro-cracks in tight reservoirs are identified by the dual-peak phenomenon of nuclear magnetic resonance T₂ spectrum and acoustic emission technology,and the recognition effect is good.According to the observations by microscopic observation,it is found that the Lucaogou Formation in the Jimusan Depression mainly develops micro-fractures of diagenesis,followed by structural microcracking,and the development of micro-fractures of particles is less.The development of microfractures is related to pore fluid content,lithology,mineral composition,and microscopic deposition.Through triaxial fracturing experiments and monitoring using acoustic emission tests,the moment of micro-cracks was identified,and the number of acoustic emission events at the time of micro-cracks was further obtained.Since the number of acoustic emission events is positively correlated with the micro-fissure density,acoustics The transmit ringing technique reflects the microcrack density.The higher the pore fluid content,the lower the compressive strength of the rock,and the faster the rate of decrease,the larger the ringing count at the site of micro-fracture,the easier to break and form micro-fractures.Through NMR experiments,the percentage of the sum of the T₂ spectrum sum of the T₂ spectrum amplitudes at each point where the T₂spectrum relaxation time is greater than 10 ms can be used to characterize the percentage of cracks/micro cracks.The higher the brittle mineral content in the rock sample,the crack/micro-crack.The greater the percentage,the easier the micro-cracks develop.In tight reservoirs,micro-fractures play a major role in controlling permeability and have little effect on rock porosity.The degree of development of micro-fractures is the key to determining the ease of reservoir development and ultimate recovery.In the cores with micro-fractures,micro-fractures are the main connecting channels between core channels,and in cores without micro-cracks,the core channels are mainly connected by tunnels.