Quantitative analysis of the influence of faults on deep in situ stress under different stress types

The study of deep geostress and stress disturbance patterns near faults is critical for ensuring the safety of ultradeep wells, optimizing the effect of fracturing stimulation and accurately predicting "engineering sweet spots". As oil and gas exploration has expanded to deeper and more complex tectonic areas, understanding the problem of fault-stress perturbation patterns under different stress backgrounds has become very urgent. In this study, to address the scientific problem in which the geostress perturbation pattern of deep (> 4500 m) faults is unclear, the Kelasu tectonic zone in the Kuqa depression was taken as the research object, and well logging data, seismic data and geomechanical modeling methods were used to systematically reveal the quantitative influence of the fault dip angle on in situ stress. The quantitative effects of the fault dip angle on the geostress under different stress types were investigated. The image logging data were used to identify wellbore breakouts and induced fractures, and the current geostress direction was confirmed to be nearly N‒S. A geological model of reverse faults with different dip angles was constructed on the basis of equilibrium section technology. The finite element numerical simulation method was used to analyze the relationship between the fault dip angle and geostress under three stress mechanisms: normal faulting, stress conversion and strike-slip faulting. The results show that in the normal fault stress field, the horizontal maximum and minimum principal stresses both decrease with increasing fault dip angle. Near the stress transformation zone, the principal stress increases slightly with increasing dip angle, but the control by faults weakens. In the strike-slip stress field, both increase significantly with increasing dip angle. In addition, the fault dip angle affects the distribution pattern of shear stress: the shear stress of low-angle faults has a wider range, whereas that of high-angle faults has stronger stress concentrations. This study has important guiding significance for geostress prediction, drilling trajectory optimization and fracturing design of deep reservoirs.