陕西汉中盆地水压致裂地应力测量分析研究

Hydrofracturing in-situ stress measurement in Hanzhong Basin,Shaanxi Province

汉中盆地位于龙门山断裂带东北段的末端,汶川MS8.0地震发生以后,地震活动存在沿龙门山断裂带向NE向发展的趋势.在汉中盆地西缘进行了两个钻孔的水压致裂地应力测量,来分析震后该区地应力状态,以期为该区的地震危险性研究提供实际资料.这两个钻孔深度均为300m左右,相距33m,取得了较好的地应力测试结果.通过对地应力测试结果的综合分析研究,得到以下认识:①在汉中盆地西缘300m深度地层内,最大水平主应力值为5.69—19.52MPa,最小水平主应力值为3.81—10.90 MPa,垂直主应力值约为1.25—7.03MPa,水平主应力占主导地位,垂直应力为最小应力,该地应力状态有利于逆断层的活动;②汉中盆地西部现今最大水平主应力方向为WNW或近EW向;③汶川地震后,目前汉中盆地及其西部地区仍处于构造应力调整阶段,总体相对稳定.

Hanzhong basin is located at the end of northeastern section of Long- menshan fault zone. After the Wenchuan Ms8. 0 earthquake, the earthquakes tend to occur mainly in the northeastern section of the Longmenshan fault and migrate towards NE direction. In order to study the stress state after the main- shock and analyze the seismic risk in Hanzhong basin region, two drillings were arranged to conduct hydrofracturing in-situ stress measurement on the western margin of Hanzhong basin. Both drillings have a depth of 300 m, the distance between the two drillings is 33 m. The results of stress measurement are per- {ect. Based on a comprehensive analysis of the stress measurement results, the following conclusions are drawn： @ On western margin of Hanzhong basin within 300 m depth, the maximum horizontal principal stress is 5.69--19.52 MPa, the minimum horizontal principal stress is 3.81--10.90 MPa, and the vertical principal stress is 1. 25--7. 03 MPa. The horizontal principal stress plays a dominant role and the minimum principal stress is vertical. The stress state is in favor of thrust fault movement. （~） The present maximum horizontal principal stress in Hanzhong basin is in WNW-ESE orientation or in EW. （~） Since the occurrence of Wenchuan Ms8. 0 earthquake, the tectonic stress in Hanzhong basin and its western neighbour region has been in an adjustment phase and being stable generally.