The roles of anisotropy in production increasing in low porosity and low permeability reservoir: an example in Sag A, East China Sea

The Sag A of the East China Sea Basin is dominated by low porosity and low permeability reservoirs. Production practice has proved that such reservoirs cannot be economically and effectively developed in conventional vertical wells or low-angle directional wells (low productivity). Therefore, it is particularly important to tackle permeability anisotropy and reservoir "sweet spot". The anisotropy characteristics of clastic rock reservoir are common in the Sag A. The results of the anisotropy experiment of 360° sub-sector of full-diameter core (permeability and sonic time difference) show that: the horizontal permeability distribution range of six sectors is (3.7～17.3)×10⁻³ μm², the axial permeability of 90° is 0.06×10⁻³ μm², and the permeability anisotropy distribution range is 62～288. The permeability in the horizontal dominant direction is 3～5 times of that in non-dominant direction. Moreover, the high permeability has a small angle between the P-wave time difference and the low S-wave time difference. Further imaging logging data and regional stress analysis confirm that the direction of maximum horizontal principal stress has a small angle with the development direction of structural fracture (permeability predominant direction). Combined with the distribution pattern of the "sweet spot" reservoir, the well distribution perpendicular to the direction of maximum horizontal principal stress is conducive to productivity release, which facilitate the economical and effective development of low permeability reservoir.