In-situ stress field and project stability of underground water-sealed oil depots

Building strategic underground water-sealed oil depots is one important access to assure the safe and stable national oil storage system. Accordingly, China is planning to build one large-scale strategic oil depot in Bohai Gulf. Due to the characteristics of special underground structures, the magnitude and orientation of in-situ stresses of the planned project range are studied and analyzed. The hydrofracturing in-situ stress measurements are done in five boreholes about 140 m deep. For the scattered measurement results, it is hard to find out the intrinsic relationships among different measurement points. Therefore, the Shoerey’s Model is taken to process all the measurements at five boreholes, and then the magnitude of stresses at the depot section is determined accurately. The maximum horizontal stress is 11.02±1.0 MPa, the minimum one is 6.82±1.0 MPa, and the orientation of the maximum horizontal stress is 76° (±13°), which coincides with the research findings by B. C. Haimson et al. in Korea. The orientation is consistent with that from the WSM, i.e., the orientation of far-field stresses in this region is between WSW-ENE and E-W. The far-field stresses are moderate and have few effects on the stability of underground structure according to the modified rock mass strength-to-stress ratio method proposed by C. H. Wang. Under such stress conditions, according to the analysis of the ratios of the maximum boundary stress to the rock mass strength, the results show that if the axis of depot is parallel to the orientation of the maximum horizontal stress, during the excavation, the linear elastic deformation is the major phenomenon in the intact wall rock mass, and falling or sliding of blocks and wedges may occur in local parts. How to arrange the depot and design its section may affect the project stability severely.