Building the underground water-sealed petroleum storage cavern is one important access to assure safe and stable national petroleum storage system. Considering these reasons, some national departments are planning to build one large-scale strategic petroleum storage project in Bohai Gulf. For the special underground structure features, magnitudes and orientation of far-field stresses of planned project area shall be studied in detail. The hydrofracturing measurements has been done in five boreholes of about 140m deep; for the scattered measurement results, it is hard to find out the intrinsic relationships between different measurement spots; therefore, the Shoerey's Model is taken to process all the measurements, and then the magnitude of stresses at the cavern section is determined accurately; the maximum horizontal stress is 11.02±1.0MPa, and minimum horizontal stress is 6.82±1.0MPa; the orientation of maximum horizontal stress is 76°(±13°), which coincides with the findings by B. C. Haimson, et al. in Korea and the data from WSM, i.e., the orientation of far-field stresses in this region should be between WSW-ENE and E-W. The far-field stresses have few effects on the stability of underground structure according to the stress-to-strength ratio method proposed by Hoek E.; during the excavation, the linear elastic response is the major phenomenon in intact wall rock mass, but falling or sliding of blocks and wedges may occur in some local parts.
With the rapid increase of petroleum consumption in China, China will depend on more and more foreign petroleum resources. According to some forecasts, the demand quantity in China till 2010 shall be about 0.27 billion tons, but the production is only about 0.17 billion tons, so almost 0.1 billion tons of petroleum shall be imported from other countries, which amounts to 40% of the annual consumption (Lee W. Y., 2002). Therefore, in order to guarantee the economic safety of China, it is necessary to establish a safe and reliable national petroleum storage system. Building underground water-sealed petroleum storage cavern is one very important access to better the national petroleum storage system (Xia X. L, 2004). Considering the above factors, some relevant departments are planning to build one large-scale underground petroleum storage cavern near the Bohai Gulf. The underground petroleum storage cavern is distinguished from other underground structures for its special functions. In general, underground petroleum storage cavern is built in the intact hard and brittle granite rock mass under the sea level, with long axis, large span and multiple spaces. For the special underground structure types, the stability of wall rock mass around cavern often dominate the entire progress of such project (Chen Q., 2006). According to the geotechnical conditions fit for underground petroleum storage cavern, the intact hard crystal rock mass often can accumulate much elastic strain energy, which is the essential lithology condition of rockburst hazard (Chen Q., 2005). Therefore, in-situ stresses, one major external inducement of rockburst, become one very important parameter to be studied in detail during the site investigation for the underground petroleum storage cavern.
