摘要
用钻孔崩落法确定了中国大陆科学钻探主钻孔5047m深度以上的现今地应力状态.由钻孔声波成像测井资料发现,科学钻主钻孔在1200m深度以下出现了钻孔崩落现象.我们从1216~5047m的深度范围内采集了143个钻孔成像测井图象资料,对钻孔崩落椭圆长轴方位进行了统计,结果表明崩落椭圆长轴平均方位为319.5°±3.5°,最大水平主应力方位平均为49.5°±3.5°.利用崩落形状要素(崩落深度和崩落宽度)以及岩石的内聚力和内摩擦角,估算了1269m至5047m范围内52个深度上的最大和最小水平主应力的大小.结果表明,在浅处1216m深度,最大水平主应力为42MPa,最小水平主应力为30.3MPa;在深处5000mm深度,最大水平主应力为160.5MPa,最小水平主应力为120MPa;地应力随深度近于线性增加.据岩石密度测井资料计算了各个深度上静负载应力.3个主应力的大小和方向反映出科学钻主孔位置的应力场处于走滑应力状态,与临近地区地震震源机制解和其他方法得到的应力场一致.利用声发射法对岩心试件进行了声发射测量,得到了最大水平主应力幅值,并与崩落法测量结果进行了对比,两者十分一致.
The breakouts began to occur under the depth of 1200m in the main borehole of Chinese Continental Scientific Drilling (CCSD), 143 breakout images are collected from acoustic borehole televiewer data between 1216m and 5047m. The average orientation of breakouts is 319.5°±3.5°. The average orientation of maximum horizontal stress is 49.5°±3.5°. Using breakout parameters measured from borehole breakouts (depth and width of breakout) and rock cohesion and inner friction angle determined from triaxial rock compression and deformation tests, the magnitudes of principal stress are calculated at 52 different depths from 1269m to 5047m. Overburden stress is calculated using the density logging data. The magnitude of maximum principal stress is determined using acoustic emissions. A comparison of measurement results of acoustic emission and borehole breakouts is carried out, and the results from the two methods are in good agreement. According to the orientations and magnitudes of three principal stresses, stress state (S_H>S_v>S_h) in the area of CCSD indicates the strike-slip stress regime and is coincident with the strike-slip stress field observed from earthquake focal plane mechanisms.