Abstract. This paper presents selected results of a broader research project pertaining to the hydraulic fracturing of oil reservoirs hosted in the siltstones and fine grained sandstones of the Bakken Formation in southeast Saskatchewan, Canada. The Bakken Formation contains significant volumes of hydrocarbon, but large-scale hydraulic fracturing is required to achieve economic production rates. The performance of hydraulic fractures is strongly dependent on fracture attributes such as length and width, which in turn are dependent on in-situ stresses. This paper reviews methods for estimating changes to the in-situ stress field (stress shadow) resulting from mechanical effects (fracture opening), poro-elastic effects, and thermo-elastic effects associated with fluid injection for hydraulic fracturing. The application of this method is illustrated for a multi-stage hydraulic fracturing operation, to predict principal horizontal stress magnitudes and orientations at each stage. A methodology is also presented for using stress shadow models to assess the potential for inducing shear failure on natural fractures. The results obtained in this work suggest that thermo and poro-elastic stresses are negligible for hydraulic fracturing in the Bakken Formation of southeast Saskatchewan, hence a mechanical stress shadow formulation is used for analyzing multistage hydraulic fracture treatments. This formulation (and a simplified version of the formulation) predicts an increase in instantaneous shut-in pressure (ISIP) that is consistent with field observations (i.e., ISIP increasing from roughly 21.6 MPa to values slightly greater than 26 MPa) for a 30-stage fracture treatment. The size of predicted zones of shear failure on natural fractures are comparable with the event clouds observed in microseismic monitoring when assumed values of 115°/65° are used for natural fracture strike/dip; however, more data on natural fracture attributes and more microseismic monitoring data for the area are required before rigorous assessment of the model is possible.

中文翻译：

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水力压裂过程中应力阴影分析的分析框架–应用于加拿大萨斯喀彻温省的巴肯组

摘要。本文介绍了有关加拿大萨斯喀彻温省东南部Bakken组粉砂岩和细粒砂岩中所含油藏水力压裂的更广泛研究项目的选定结果。巴肯组含大量碳氢化合物，但需要大规模的水力压裂才能达到经济的生产率。水力压裂的性能在很大程度上取决于诸如长度和宽度之类的压裂属性，而这些属性又取决于原地应力。本文概述了估算与水力压裂注水相关的机械效应（裂缝开口），孔隙弹性效应和热弹性效应引起的地应力场变化（应力阴影）的方法。说明了该方法在多阶段水力压裂作业中的应用，以预测每个阶段的主要水平应力大小和方向。还提出了使用应力阴影模型评估在自然裂缝上诱发剪切破坏的可能性的方法。这项工作获得的结果表明，在萨斯喀彻温省东南部的巴肯组，水力压裂的热应力和孔隙弹性应力可以忽略不计，因此采用机械应力阴影公式来分析多级水力压裂处理。该公式（以及该公式的简化版本）预测瞬时关闭压力（ISIP）的增加与现场观察一致（即ISIP从大约21开始增加）。6兆帕的压力值略高于26兆帕的压力）进行30阶段的断裂处理。当假定115°/ 65°的假定值用于自然裂缝走向/倾角时，天然裂缝上预测的剪切破坏区域的大小与微震监测中观察到的事件云相当。但是，在对该模型进行严格评估之前，需要更多有关该地区天然裂缝属性的数据和更多的微震监测数据。