利用成像测井资料分析汶川地震断裂带科学钻探3号孔(WFSD-3)裂缝特征

WFSD-3孔是汶川地震断裂带科学钻探主要钻孔之一,全井段(终孔深度1 502.30 m)实施了连续取心(累计取心进尺1 548.44 m)和测井作业。采集到的成像测井资料包含丰富的原位地质特征信息,对裂缝、破碎带识别和构造应力场分析具有重要作用。利用该钻孔的电阻率成像测井和超声成像测井资料,结合岩心资料进行了裂缝特征分析。结果表明,WFSD-3孔岩层高角度斜交缝最为发育,其次是低角度斜交缝,垂直缝和水平缝极少;25～200 m和900～1 000 m深度范围内裂缝尤为发育;不同深度的裂缝倾向存在明显差异:410 m之上主要分布于260°～290°,410～730m集中于330°～360°,730～960 m主要分布于210°～240°,960～1 185 m与410 m之上基本一致,1 410～1 450 m与前述各深度段不同,集中于180°～200°;裂缝与破碎带、层理密切相关,宏观分布受构造控制。

Fracture Characterization Using Image Logging in Borehole 3 of Wenchuan Earthquake Fault Zone Scientific Drilling (WFSD-3)

The borehole of WFSD-3 is a main hole of the Wenchuan Earthquake Fault Zone Scientific Drilling.The continuous coring(total length of 1,548.44 m) and logging data of borehole WFSD-3 have been acquired.The image logging data of borehole WFSD-3 contain a mass of in-situ geological feature information,which plays an important role in the identification of fractures,fracture zones and in the analysis of tectonic stress field.Using the resistivity and acoustic image logging data in conjunction with core data,the identification and analysis of fracture characterization were carried out.The results show that in the strata of borehole WFSD-3,high-angle oblique crossing fractures develop dominantly,followed by low-angle oblique crossing fractures.Vertical and horizontal fractures are rare.The fractures particularly develop at intervals of 25 m to 200 m and 900 m to 1,000 m in borehole WFSD-3.The main dip directions of fractures at different depths are obviously different:(1) above 410 m the main dip directions of fractures are between 260° and 290°;(2) from 410 m to 730 m,the main dip directions are between 330° and 360°;(3) from 730 m to 960 m,the main dip directions are between 210° and 240°;(4) from 960 m to 1,185 m,the main dip directions are basically consistent with those above 410 m;(5) from 1,410 m to 1,450 m,the fractures are different from those of the depths above with the main dip directions between 180° and 200°.Fractures are closely related to fracture zones and beddings,and the macro distribution of fractures is controlled by tectonics.