Research On The Logging Evaluation Method Of Medium-deep Gas Reservoirs In The NO.5 Tectonic Zone Of Nanpu Sag

Affected by provenance and sedimentary environment,the intermediate and deep gas reservoir of the Nanpu-5 structure has small reservoir space,bad permeability,complex pore structures,various types of pore.The pore fluid has little contribution to the logging response.The logging response of gas and water has little difference or even mixed sometimes,which increases the difficulty of fluid identification.According to the situation of the study area,the lithology,physical property,electrical property,gas-bearing property and pore structure of the intermediate and deep gas-bearing sandstone reservoir with low porosity and permeability are analyzed systematically.Based on NMR experiments,combined with mercury injection curves,the pore structures and reservoir property are studied.Based on core scale logging and flow zone index,the interpretation model of pore and permeability is established.Based on the litho-electric experiments,the Archie parameters are analyzed and the saturation formula is established.Based on rock acoustic experiments,the sensitivity of the P-and S-wave velocity to the gas of the reservoir is studied.The gas identification methods such as combination method of well loggings,P-and S-wave indication method and dual P-wave curve overlapping are studied in detail.After studying the response of NMR T₂ and S-wave velocity to the pore structure,the relationship of geometric mean of T₂ and S-wave velocity is established,and then the gas identification chart combining NMR and acoustics characteristic is established.The S-wave forecast using geometric mean of NMR T₂ are explored.The results show that there are four types of pore structures in the target area.The pore scale and the coordination relations of large and small throat determine the storage capability and permeability of four pore structure.The P-wave velocity of the intermediate and deep gas reservoir is sensitive to gas-bearing properties.The compressional slowness and ratios of the P-and S-wave velocity cross plots,the ratios of the P-and S-wave velocity cross plots and the bulk modulus and Poisson ratio cross plots identify the gas reservoir well.The geometric mean of T₂ and S-wave velocity present a power function,which benefits S-wave forecast using NMR logging.The compressional slowness and geometric mean of T₂ cross plot is established,which works well in identifying the gas-bearing reservoir.