We performed an analysis of present-day stress profiles for four wells penetrating the Lower Palaeozoic shale sequence of the Baltic Basin (northern Poland). Breakouts, hydraulic fracturing and leak-off tests were used to calibrate stress models based on anisotropic elastic shale properties. Initial stress models, balancing the lengths of the modelled and observed breakouts, indicated a degradation of the mechanical properties reconstructed from the density and dipole acoustic tool logs. Taking this adverse effect into account, final stress models were calculated which showed a stratification of the stress regime consistent with the lithostratigraphic shale units. A clear dominance of the horizontal stress-generating gravity factor over the horizontal tectonic strain was demonstrated. The obtained values of tectonic strain in the shale sequence compared to the previously determined strain in the crystalline basement of the same study area suggest a significant role of viscoelastic relaxation of the shale sequence.

中文翻译：

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从钻孔数据推断的波兰北部波罗的海盆地下古生代页岩层序的当今应力分层


我们对穿透波罗的海盆地（波兰北部）下古生代页岩序列的四口井的当今应力剖面进行了分析。突破、水力压裂和泄漏测试用于校准基于各向异性弹性页岩特性的应力模型。初始应力模型平衡了建模和观察到的突破的长度，表明从密度和偶极子声学工具测井重建的机械性能退化。考虑到这种不利影响，计算了最终的应力模型，该模型显示了与岩石页岩单元一致的应力状态分层。证明了水平应力产生重力因子对水平构造应变的明显主导地位。与先前确定的同一研究区结晶基底中的应变相比，页岩层序中构造应变的结果表明页岩层序的粘弹性松弛起着重要作用。