Measurement and distribution of horizontal minimum principle stress of shale reservoir

Key words:  horizontal minimum principal stress  hydraulic fracturing in situ stress measurement method  shale reservoir  plastic mineral content  deep shale gas

Abstract:

The horizontal minimum principal stress is a key parameter for hydraulic fracturing design of unconventional reservoirs. In this study, the horizontal minimum principal stress was obtained using an in situ stress measurement method while hydraulic fracturing in the Niutitang Formation of Cambrian at the southeast area of Guizhou province. The horizontal minimum principal stress is 24.9-25.3 MPa at the depth of 1179-1187 m with the interval of clayey siltstone, and it is 21.4 MPa at the depth of 1207-1208 m intercalated within limestone. Referring to the in situ stress measurement results of similar formations, the distribution of the in situ stress magnitude within the shale formation was evaluated. The results show that the magnitude of the horizontal minimum principal stress in shale reservoir is mainly controlled by the formation lithology which increases obviously with the increase of the content of plastic minerals such as clay. Under the action of regional tectonic stress field, the horizontal minimum principal stress of shale is 4-15 MPa higher than that of sandstone or limestone. The research results can be used for quantitative evaluation of the in situ stress difference between shale and brittle interbed formations. For deep shale gas reservoirs, layers with high brittle mineral content and low value of horizontal minimum principal stress are recommended for horizontal wells, which are conducive to the initiation and propagation of fractures, and have low closure pressure after fracturing operation.