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首页> 外文期刊>Journal of natural gas science and engineering >Imbibition inducing tensile fractures and its influence on in-situ stress analyses: A case study of shale gas drilling
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Imbibition inducing tensile fractures and its influence on in-situ stress analyses: A case study of shale gas drilling

机译：诱导诱发拉伸断裂及其对原位应力分析的影响：以页岩气钻探为例

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For conventional oil and gas reservoirs, the orientation and magnitude of in-situ stress can be estimated by analyzing wellbore failures such as borehole breakouts and drilling induced fractures (DIF) using Zoback's stress polygon model. According to this model, DIFs are most likely induced by the high mud weight, wellbore cooling, high stress difference, or pressure surge. A large number of DIFs have been identified by imaging logging in shallow well sections of shale gas well QY1 in the Sichuan Basin of China. However, all possible explanations of standard DIFs do not work well, suggesting the limitations of this model when applied to shale formations. Other mechanisms influence the formation of DIFs in this shale gas well that are not covered in this model. In this paper, the orientation and magnitude of the insitu stress in the study area are constrained following the general procedure outlined by Zoback's stress polygon model. The DIF distribution in the QY1 wellbore and its relationship with organic matter are then analyzed. A new mechanism was introduced to explain the DIFs in the organic-rich section. The results show that the maximum horizontal stress (SHmax) in the study area trends N95 degrees E +/- 9 degrees. The calculated in-situ stress magnitudes are consistent with a strike/reverse faulting stress regime (SHmax > Sv approximate to Shmin). In addition, the DIFs are concentrated in the organic-rich interval. For organicrich shale, strong water imbibition is common, which is related to super-dry gas shale due to the water displacement of kerogen-transformed hydrocarbons, high capillary pressure due to micro-nano meter pore diameters, and the water-sensitive clay mineralogy. This spontaneous water intake generates the effective internal stress around the wellbore, producing DIFs in the shale gas well. The introduction of this new mechanism allows the Zoback's stress polygon model to constrain the in-situ stress in the study area. Therefore, this mechanism should be considered during estimation of the in-situ stress in gas shale formation when using Zoback's stress polygon model. (C) 2015 Elsevier B.V. All rights reserved.
机译：对于常规的油气藏，可以通过使用Zoback应力多边形模型分析井眼故障（例如井眼破裂和钻井诱发的裂缝（DIF））来估计地应力的方向和大小。根据该模型，DIF最有可能是由高泥浆重量，井筒冷却，高应力差或压力波动引起的。通过对中国四川盆地页岩气QY1井浅井段进行成像测井，已经发现了大量DIF。但是，所有对标准DIF的可能解释都不能很好地起作用，这表明该模型在应用于页岩地层时的局限性。其他影响该页岩气井中DIF形成的机制未在此模型中涵盖。在本文中，按照Zoback应力多边形模型概述的一般步骤来约束研究区域中原位应力的方向和大小。然后分析了QY1井眼中DIF的分布及其与有机质的关系。引入了一种新的机制来解释富含有机物的部分中的DIF。结果表明，研究区域中的最大水平应力（SHmax）趋向于N95度E +/- 9度。计算得出的原地应力大小与走向/逆断层应力状态（SHmax> Sv近似于Shmin）一致。另外，DIF集中在富含有机物的区间。对于富含有机质的页岩，吸水很普遍，这与超级干燥的页岩有关，这是由于干酪根转化的碳氢化合物的水置换，由于微纳米孔径引起的高毛细压力以及对水敏感的粘土矿物学。自发的进水会在井眼周围产生有效的内部应力，从而在页岩气井中产生DIF。这种新机制的引入使Zoback的应力多边形模型可以约束研究区域中的原地应力。因此，在使用Zoback应力多边形模型估算气页岩地层原位应力时，应考虑该机制。 （C）2015 Elsevier B.V.保留所有权利。

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