Logging identification method for small fault based on stress anisotropy and crustal stress types

A logging identification method for a small fault based on stress anisotropy and crustal stress types, comprising:

• step 1, carrying out logging calculation on a current crustal stress:
• calculating a horizontal principal stress with logging data:
• S
• H
• ⁢
• max
• =
• v
• 1
• -
• v
• ⁢
• σ
• v
• -
• v
• 1
• -
• v
• ⁢
• α
• ⁢
• P
• p
• +
• α
• ⁢
• P
• p
• +
• E
• 1
• -
• v
• 2
• ⁢
• ε
• y
• +
• vE
• 1
• -
• v
• 2
• ⁢
• ε
• x
• (
• 1
• )
• S
• h
• ⁢
• min
• =
• v
• 1
• -
• v
• ⁢
• σ
• v
• -
• v
• 1
• -
• v
• ⁢
• α
• ⁢
• P
• p
• +
• α
• ⁢
• P
• p
• +
• E
• 1
• -
• v
• 2
• ⁢
• ε
• x
• +
• vE
• 1
• -
• v
• 2
• ⁢
• ε
• y
• (
• 2
• )
• wherein in equations (1)-(2), Shmin and SHmax indicate a minimum horizontal principal stress and a maximum horizontal principal stress respectively, in MPa, v indicates a static Poisson's ratio, σv indicates an overburden pressure, in MPa, α indicates a Biot's elastic coefficient, and is dimensionless, Pp indicates a pore pressure, in MPa, E indicates a static Young's modulus, in MPa, εx and εy indicate strains in directions of the minimum horizontal principal stress and the maximum horizontal principal stress respectively, and are dimensionless, and εx and εy are mainly configured to characterize an additional horizontal crustal stress caused by a tectonic stress, and are dimensionless;
• step 2, calculating stress anisotropy:
• establishing, according to equation (3), a stress anisotropy index Kh to calculate the stress anisotropy:
• K
• h
• =
• S
• Hmax
• -
• S
• hmin
• S
• hmin
• (
• 3
• )
• wherein in equation (3), Shmin and SHmax indicate a minimum horizontal principal stress and a maximum horizontal principal stress respectively, in MPa;
• and the stress anisotropy is calculated with equation (3) in a vertical direction;
• step 3, determining a direction of the current crustal stress:
• determining the direction of the current crustal stress in the vertical direction by integrating borehole wall collapse, hole deviation, induced fractures and an orientation of fast shear waves;
• step 4, determining a transformation location of a crustal stress type:
• identifying, according to a determined magnitude and direction of the current crustal stress, the crustal stress type to determine the transformation location of the crustal stress type, wherein the crustal stress type comprises a strike-slip stress field, a thrust stress field and a normal fault stress field;
• step 5, determining a development location and strike of the small fault:
• determining the development location of the small fault according to the transformation location of the crustal stress type, and determining an included angle between the current crustal stress and the fault according to an amplitude of variation of the stress anisotropy;
• wherein the determining an included angle between the current crustal stress and the fault according to an amplitude of variation of the stress anisotropy comprises:
• determining the strike of the fault on the basis that the fault intersects with the direction of the current crustal stress at an acute angle at a location in which the stress anisotropy is increased and the fault intersects with the direction of the current crustal stress at an obtuse angle at a location in which the stress anisotropy is reduced;
• and establishing, by building geomechanical models of the fault in different directions, a quantitative relation between an included angle between the strike of the fault and a direction of the horizontal principal stress and the stress anisotropy index, to accurately determine the strike of the fault;
• and
• step 6, guiding exploration and development of a complex oil and gas reservoir and construction of a gas storage according to the development location of the fault and the strike of the fault.