关键词: 井壁崩落, 构造应力场, 大民屯

Abstract: The basic principle and method of crustal stress measurement by borehole breakouts are introduced in this paper,and some problems in determining the direction of the horizontal principal stresses from the shear rupture of the borehole walls are discussed.Several thousand groups of data obtained from the logs of four-arm dipmeter of 15 oil wells in Damintun depression of Liaohe oil field were collected.Basing on the statistics and analyses of these data,we calculate the predominant direction of the long axes of borehole breakout ellipses in each oil well at different depths in order to reveal the variation of the principal stress directions with depth.On the basis of the predominant directions of the long axes of borehole breakout ellipses,we calculate and acquire the predominant directions of the maximum horizontal principal stress at different depths for all15oil wells.The results show that the predominant direction of the long axes of the borehole breakout ellipses is about N10°W—N10°E,while the predominant direction of the maximum horizontal principal stress is about N80°～100°E,with a mean of N90°E and a general trend of NEE.This conclusion coincides well with the values obtained from focal mechanism solutions.The variation of the predominant direction of the maximum horizontal principal stress with depth is relatively small,about10°～15°.This may indicate that the direction of modern tectonic stress field in Damintun depression of Liaohe oil field is stable and is possibly controlled by the same tectonic stress field.

Key words: Damintun, borehole breakout, tectonic stress direction