In situ stress and natural fracture effectiveness in Luzhou shale reservoir, southern Sichuan Basin

Abstract

This study analyzed the present-day in situ stress field characteristics in the Longmaxi Formation of Luzhou area using methods of comprehensive logging calculations, numerical simulations, etc. Further, this paper analyzed and quantitatively evaluated the mechanical effectiveness of natural fractures in the target layer based on the relationship between in situ stresses and natural fracture development. The results reveal that the dominant orientation of present-day in situ stress in the Layer S₁l^1-1 is WNW-ESE-trending in the Luzhou area, affecting by local structures. The horizontal maximum principal stress in the Layer S₁l^1-1 ranges from 70 MPa to 125 MPa, with the majority between 85 MPa and 110 MPa. The horizontal minimum principal stress varies from 50 MPa to 100 MPa, predominantly falling between 75 MPa and 90 MPa. The stress distribution exhibits strong heterogeneous characteristics, significantly influenced by tectonic activity. Under the present-day in situ stress state, mechanically effective natural fractures constitute a small portion of the total fractures. The effectiveness is mainly influenced by factors such as fracture inclination, fault zone development, and the orientation of stress relative to fracture strike. The results are expected to support shale gas exploration and development in the Longmaxi Formation of Luzhou area, Sichuan Basin.

Graphical abstract

Keywords

present-day in situ stress field / natural fracture / effectiveness evaluation / Longmaxi formation / Luzhou area

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