Shining light on shale: geomechanics and 4D fracture characterization

英国页岩气工业的成功发展可以得益于对这些岩石的裂缝和物理性质的更好理解。决定裂缝如何萌生和生长的关键岩石物理性质取决于岩石中裂缝的大小。这些特性的实验室测量对于成功的水力压裂模拟研究，从而优化生产是必不可少的。在这项研究中，将使用一系列创新技术，包括首次通过同步加速器X射线层析成像以及利用声发射定位裂缝扩展事件，对岩石内部的水力裂缝生长进行3D观察和量化。这将显示水力压裂是如何形成和发展的，先前存在的缺陷在其形成过程中所起的作用，启动它们所需的流体压力，以及如何改变其形式以优化天然气生产。对结果的解释依赖于对强度、摩擦力和抗裂性的平行测量，以及对流体的渗透性，因为岩石强度取决于流体可以穿透其孔隙的程度。这些性质还受页岩的矿物学、有机含量和微结构的影响。因此，我们将测试几个具有不同此类特征的页岩。这些特性还决定着井眼的稳定性，但方式尚不清楚。页岩对气体和液体的渗透率也是已知的，它取决于给定埋藏深度下孔隙中流体压力的值，因此，随着生产过程中气体压力的降低，页岩渗透率也会发生变化。了解这种压力敏感性对于成功解释试井是至关重要的，必须根据试井中的天然气和可能的储层产量进行估计。因此，这项研究将产生可能对页岩气开采的一系列方面产生影响的结果。

The successful development of a shale gas industry in the UK can be aided by improved understanding of the fracture and physical properties of these rocks. The key petrophysical properties that determine how fractures initiate and grow are determined on the scale of flaws in the rock. Laboratory measurements of these properties are essential to successful modelling studies of hydraulic fracture, and hence optimisation of production. In this research a range of innovative technologies will be used including, for the first time, 3D observation and quantification of hydrofracture growth with time inside the rock by means of synchrotron X-ray tomography coupled with location of crack growth events using acoustic emissions. This will show how hydrofractures initiate and develop, the role of pre-existing flaws in their initiation, the amount of fluid pressure required to initiate them, and how their form might be modified to optimize gas production. Interpretation of the results depends on parallel measurements of the strength, friction and resistance to fracture, and also permeability to fluids, because rock strength depends on the extent to which fluids can penetrate their pores. These properties are also affected by the mineralogy, organic content and microstructure of the shale. Therefore we will test several shales with different such characteristics. These properties also determine, in ways yet to be understood, the stability of boreholes. Permeability of shales to gas and liquids is also known to depend on value of the fluid pressure in the pores for a given depth of burial, thus it changes as gas pressure is drawn down by production. Knowledge of this pressure sensitivity is essential for the successful interpretation of well tests, from which gas in place and likely reservoir yield must be estimated. Thus this research will produce results that can impact on a range of aspects of shale gas exploitation.