The in situ stress determination from borehole image logs in the Kuqa Depression

The Kuqa Depression is located in the northern part of Tarim Basin and is adjacent to the southern Tianshan orogen, which is subject to strong tectonic compression since the Neogene period and is extremely active at present. The accurate determination of the in situ maximum horizontal stress (SHmax) is important for stress-related geo-hazards and reservoir-related issues, such as borehole stability, horizontal well design, completion, sanding and fracture conductivity in fractured reservoirs in the Kuqa Depression. A borehole image technique is an effective method for stress determination in oil fields and is abundantly measured in the Kuqa Depression, including in water-based and oil-based mud environments. Based on 1954.08 m drilling-induced fractures and 3576.04 m borehole breakouts derived from imaging logs in 72 gas wells, SHmax values were determined in different tectonic units in the Kuqa Depression. The in situ stress direction from the west to east section in the depression shows an approximately clockwise rotation from NW to NE trending, which is consistent with the results derived from focal mechanism solution. Both conventional logging and borehole breakout can be well used for stress magnitude determination, while breakout is more preferable. The calculation of stress magnitude infers that the present-day regional stress intensity may be decreasing to the southward direction in the Kuqa Depression.