Regional evaluation method of ground stress in shale oil reservoirs-taking the Triassic Yanchang formation in northern Shaanxi area as an example

Estimating in-situ stress in shale oil reservoirs is critical for predicting hydraulic fracture height. However, the varied longitudinal lithology and transverse isotropy challenge the regional evaluation of ground stress. A new method based on the Kaiser effect method and the Sn Model was proposed to evaluate regional ground stress from point to point. Kaiser tests obtained the regional tectonic stress coefficients. Combined with the dynamic and static transformation of elastic parameters, the Sn ground stress calculation model suitable for the Northern Shaanxi Area was constructed. According to the calculation results of ground stress in the Chang 7 section of 600 wells in this region, the plane distribution maps of maximum horizontal ground stress (SH) and the difference between SH and Minimum horizontal stress (Sh) were drawn. It was found that the SH in this area was between 20 and 60 MPa, and the So was between 2.6 and 8.8 MPa. Compared with the 3D finite element method simulation results, the forward modeling results coincided well with the inversion results in this research. The causes of the plane distribution of ground stress in the Chang 7 section were explained by regional tectonic stress and paleo topography. It was found that the movement of plate and shell and deposition were critical factors of regional ground stress distribution. The research results provide a reference for further integration of geologic and engineering in evaluating shale oil reservoirs.

Automated summary

This study proposes a new method based on the Kaiser effect method and Sn Model to evaluate the ground stress distribution in shale oil reservoirs. Through calculation and simulation, it is found that regional tectonic stress and paleo topography are the main influencing factors of ground stress distribution in the Chang 7 section.