《Table 2 The porosity values of wells》

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《"Tertiary hydrothermal activity and its effect on reservoir properties in the Xihu Depression, East China Sea"》

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The sample location is marked on the well profile in Fig.12

As depth increases，the porosity and permeability of the403 samples from the five wells（G1，G2，J1，J2，Q2），which were not affected by the hydrothermal alteration and lie distal to any faults decreases.The 442 samples from wells W1，W4，W5，W7，which were affected by hydrothermal activity，showed abnormally high porosity at intervals of approximately 2400–2500 m，3400–3500 m，and 4000–4300 m depth（Fig.12），with average values reaching 23.1%，19.6%，and 17.5%，respectively.As an example，the porosity at 3441 m in well W1was as high as 20%and showed pores with an average pore-throat radius of 13.2μm.The maximum porosity of well W6 between 3964 and 4175 m was as high as 14.6%with an average pore-throat radius of 4.12μm（these data were provided by Sinopec Shanghai Oil and Gas Branch）.The mercury injection capillary pressure（MICP）analysis revealed that the pore-throat radius ranged from1 to 40μm.The pore-throat assemblages were mainly medium pores with medium throats，small numbers of large pores with large throats and small pores with thin throats（Fig.12）.Based on thin section examination，the main types of pores present have been categorized and include combinations of interparticle dissolution pores，interparticle pores，intraparticle dissolution pores，interparticle micropores，moldic pores and dissolution vugs.Well W1 located in the Baoshi Fault Zone and affected by hydrothermal fluids，encountered tuffaceous rocks at3200 m.At this depth，quartz particles in the reservoirs were subjected to brittle fracturing and alteration，and vitrinite reflectance was abnormally high.Andesite，diorite，tuffaceous rocks，and altered dacitic rock were found at approximately 4800 m in well W6 which was located in the Chunxiao Fault Zone.The vitrinite reflectance in mudstones at this depth reached 1.35%.At a depth of 3840–4275 m，well W7 located in the Tianwaitian Fault Zone and affected by hydrothermal fluids，encountered tuff breccia，tuff，granite，granodiorite rocks.At these depths，the maximum porosity was 25.9%and the minimum was 1.5%，and the average value was 14.5%（Table 2）.44%of the sand thickness（29.5 m）of the Pinghu Formation was seen to have porosities greater than14%（3516–4645 m）（Fig.12） .