Shining light on shale: geomechanics and 4D fracture characterization

英国页岩气行业的成功发展离不开对这些岩石裂缝和物理性质的进一步了解。决定裂缝如何形成和发展的关键岩石物理性质取决于岩石中缺陷的规模。这些特性的实验室测量对于成功的水力压裂建模研究至关重要，从而优化生产。在这项研究中，将使用一系列创新技术，包括首次使用同步x射线断层扫描技术对岩石内水力裂缝随时间的生长进行3D观察和量化，并利用声发射对裂缝生长事件进行定位。这将显示水力裂缝是如何形成和发展的，预先存在的缺陷在裂缝形成过程中的作用，形成裂缝所需的流体压力，以及如何改变裂缝的形态以优化天然气产量。对结果的解释取决于对强度、摩擦、抗破裂以及流体渗透率的平行测量，因为岩石的强度取决于流体能穿透其孔隙的程度。这些性质还受页岩矿物学、有机质含量和微观结构的影响。因此，我们将测试几种具有不同特征的页岩。这些性质也以尚未被理解的方式决定了钻孔的稳定性。众所周知，页岩对气体和液体的渗透率也取决于给定埋藏深度下孔隙中的流体压力值，因此它随着生产过程中气体压力的降低而变化。了解这种压力敏感性对于成功解释试井至关重要，因为必须根据试井来估计现有气藏和可能的储层产量。因此，这项研究的结果将对页岩气开采的一系列方面产生影响。

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.