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

摘要： 文中介绍了井壁崩落法地应力测量的基本原理和方法,并利用此方法对辽河油田大民屯凹陷地区 15口井的地层倾角测井资料进行了统计和分析,绘制了崩落椭圆长轴优势方位图。结果表明,该地区井壁崩落椭圆的长轴优势方位为350°～10°,由此确定的最大主应力方向为80°～100°,平均为90°,与用震源机制解得出的结果基本相符,说明该地区的构造应力场方向比较稳定,处于同一构造应力场的作用之下。

关键词: 井壁崩落, 构造应力场, 大民屯