In-situ stress measurement and inversion analysis of the deep shaft project area in Sanshan Island based on hydraulic fracturing method

Abstract

The proposed 2000-meter-deep auxiliary shaft at the Xiling mine, Sanshan Island, Shandong Province, is an ultra-deep shaft construction project. Revealing the characteristics of the in-situ stress field in the shaft construction area is one of the necessary prerequisites for the design and construction of the shaft. We measured the in-situ stress in the deep shaft by hydraulic fracturing method to a depth of 1899.00 m and inverted the 2017.56-meter-deep in-situ stress field in the shaft construction area by numerical simulation. The results show that the maximum horizontal principal stress (SH) ranges from 23.16 to 70.86 MPa, and the minimum horizontal principal stress (Sh) from 15.24 to 47.06 MPa in the depth range from 357.76 to 1899.00 m in the borehole tested by hydraulic fracturing; the principal stress increases nearly linearly with depth, and the measured maximum horizontal principal stress directions in the measured boreholes are NW 55.5°, NW 60.4°, and NW 58.4°, respectively. Horizontal stress mainly dominates the stress field in the shaft engineering area, the vertical stress (Sv) below 1200.00 m is the intermediate stress, and the average value of the ratio of SH to Sv is 1.53. The in-situ stress field distribution pattern in the well-construction area with depth and stratigraphic changes is obtained by inversion analysis of FLAC 3D software. The inversion results are basically consistent with the measured values. It provides the fundamental scientific basis for shaft wall design and engineering risk assessment of shaft projects.

Keywords

• deep shaft
• deep strata
• hydraulic fracturing
• in-situ stress measurement
• in-situ stress inversion