Subsurface S_HMAX determined from a borehole image log, onshore southern East Coast Basin, New Zealand

Understanding the <i>in-situ</i> stress field in the subsurface provides insights on the tectonic processes and seismic hazards of a basin. This paper presents observations and interpretations of present day maximum horizontal stress (S_Hmax) orientation from well Ranui-2 located in the onshore southern East Coast Basin. Fractures identified in the Ranui-2 image log have been divided into distinct subsets based on fracture orientation. These subsets correspond in a general sense, to changes in lithology in the well, which are associated with changes in formations. Analysis of the image log shows the present day S_Hmax in the borehole has two primary stress directions, W–E and NW–SE, and most of the fractures strike NE–SW. The change in S_Hmax occurs at a depth of <i>circa.</i> 1130 m measured depth (918 m true vertical depth subsea), below the depth at which the borehole changes from vertical to ≥10° deviation. When these data are compared to the regional stress field obtained using other stress indicators such as earthquake focal mechanisms, the results are consistent with each other. This study shows that shallow subsurface indications of present-day S_Hmax in southeastern North Island reflect S_Hmax orientations from deeper within the subsurface.

探明地下原位应力场（in-situ stress field），可为盆地构造过程与地震灾害研究提供关键认知。本文针对位于东海岸盆地南部陆上的拉努伊-2（Ranui-2）井，开展现今最大水平主应力（S_Hmax）方位的观测与解释工作。研究人员依据裂缝方位，将拉努伊-2井成像测井（image log）中识别出的裂缝划分为多个不同子集；这些裂缝子集大体对应井筒内的岩性变化，而岩性变化与地层演化紧密相关。对成像测井资料的分析显示，井筒内现今最大水平主应力存在两个主要方向：西-东向与北西-南东向，且绝大多数裂缝的走向为北东-南西向。最大水平主应力的方向转变发生在测量井深约1130米（水下真实垂直深度918米）处，该深度位于井筒由垂直转向偏斜角≥10°的位置下方。将本次研究数据与通过地震震源机制（earthquake focal mechanisms）等其他应力指标获取的区域应力场进行对比后，二者结果具有良好一致性。本研究表明，新西兰北岛东南部浅部地下所反映的现今最大水平主应力方位，与地下深部的最大水平主应力方位相一致。

搜集汇总

背景与挑战

背景概述

该数据集基于新西兰南东海岸盆地陆上Ranui-2井的钻孔图像测井数据，分析了次地表现今最大水平应力（S_HMAX）的方向和特征。研究发现应力方向主要为W–E和NW–SE，裂缝走向为NE–SW，应力变化发生在约1130米深度处，与区域应力场一致，为理解盆地构造和地震灾害提供了关键数据。数据集包含原始测井数据，发布于2019年，受新西兰政府资助，适用于环境科学和地质学研究。