Abstract Faults are susceptible to reactivation during coal mining subsidence. The effects may be the generation of a scarp along the ground surface that may or may not be accompanied by associated ground deformation including fissuring or compression. Reactivated faults vary considerably in their occurrence, height, length and geometry. Some reactivated faults may not be recognizable along the ground surface, known only to those who have measured the ground movements or who are familiar with the associated subtle ground deformations. In comparison, other reactivated faults generate scarps up to several metres high and many kilometres long, often accompanied by widespread fissuring of the ground surface. Mining subsidence-induced reactivated faults have caused damage to roads, structures and land. The objective of this chapter is to provide a general overview of the occurrence and characteristics of fault reactivation in the UK.

ABSTRACT Shales are enigmatic rock types with compositional and textural heterogeneity across a range of scales. This work addresses pore- to core-scale mechanical heterogeneity of Cretaceous Mancos Shale, a thick mudstone with widespread occurrence across the western interior of the United States. Examination of a ~100 m (~328 ft) core from the eastern San Juan Basin, New Mexico, suggests division into seven lithofacies, encompassing mudstones, sandy mudstones, and muddy sandstones, displaying different degrees of bioturbation. Ultrasonic velocity measurements show small measurable differences between the lithofacies types, and these are explained in terms of differences in allogenic (clay and sand) and authigenic (carbonate cement) mineralogy. Variations in ultrasonic velocities can be related to well log velocity profiles, which allow correlation across much of the eastern San Juan Basin. A quarry block of Mancos Shale from eastern Utah, USA, a common target for unconventional exploration and ultrasonically, compositionally, and texturally similar to the laminated muddy sandstone (LMS) lithofacies of the San Juan core, is examined to sublaminae or micro-lithofacies scales using optical petrographic and electron microscopy. This is mapped to results from axisymmetric compression (ASC) and indirect tensile strength testing of this facies at the core-plug scale and nanoindentation measurements at the micron scale. As anticipated, there is a marked difference in elastic and failure response in axisymmetric and cylinder splitting tests relating to loading orientation with respect to bedding or lamination. Shear bands and Mode-I fractures display contrasting fabric when produced at low or high angles with respect to lamination. Nanoindentation, mineralogy distribution based on MAPS (modular automated processing system) technique, and high-resolution backscattered electron images show the effect of composition, texture phases, and interfaces of phases on mechanical properties. A range of Young’s moduli from nanoindentation is generally larger by a factor of 1–4 compared with ASC results, showing the important effect of pores, microcracks, and bedding boundaries on bulk elastic response. Together these data sets show the influence of cement distribution on mechanical response. Variations in micro-lithofacies are first-order factors in determining the mechanical response of this important Mancos constituent and are likely responsible for its success in hydrofracture-based recovery operations as compared with other Mancos lithofacies types.

ABSTRACT We have identified 57 large-magnitude, sequence boundaries in the Phanerozoic succession of the Canadian High Arctic. The characteristics of the boundaries, which include angular unconformities and significant changes in depositional and tectonic regimes across the boundaries, indicate that they were primarily generated by tectonics rather than by eustasy. Boundary frequency averages 10 million years throughout the Phanerozoic and there is no notable variation in this frequency. It is interpreted that each boundary was generated during a tectonic episode that lasted two million years or less. Each episode began with uplift of the basin margins and pronounced regression. This was followed by a rapid subsidence and the flooding of the basin margins. Each tectonic episode was terminated by a return to slow, long-term subsidence related to basin forming mechanisms such as thermal decay. The tectonic episodes were separated by longer intervals of tectonic quiescence characterized by slow subsidence and basin filling. The tectonic episodes are interpreted to be the product of changes in lithospheric stress fields with uplift being related to increased, compressional horizontal stress and the following time of rapid subsidence reflecting a decrease in such stresses or an increase in tensional stresses. Conversely, the longer intervals of tectonic quiescence would reflect relatively stable, horizontal stress fields. The episodic changes in stress fields affecting the Canadian High Arctic throughout the Phanerozoic may be a product of intermittent, plate tectonic reorganizations that involved changes in the speed and directions of plate movements. The longer intervals of tectonic quiescence would occur during times of quasi-equilibrium in the plate tectonic mosaic. The tectonic episodes that generated the sequence boundaries were governed by nonlinear dynamics and chaotic behavior, and there is a one-in-10-million chance that a tectonic episode will be initiated in the Canadian High Arctic in any given year. Thus, the major transgression associated with each episode can be referred to as a “10-million-year flood.”

Understanding reservoir performance and predicting hydrocarbon recovery in carbonate reservoirs are challenging due to the complexity of the pore system and the dynamic interplay of multiphase fluids that move through the pore network. A multiyear study of carbonate reservoirs across a broad spectrum of geologic conditions, fluid types, and field maturities has resulted in key insights on the links between pore-system characteristics and dynamic fluid-flow behavior with material relevance to carbonate resource assessment, field development optimization, and maximizing ultimate recovery. Pore-system heterogeneity is a primary control on hydrocarbon displacement efficiency. Multiphase flow through heterogeneous pore systems with a mix of pore types results in lower recovery than flow through more homogeneous pore systems. Due to the homogeneous nature of the micropore system, rocks dominated by micropores can have favorable hydrocarbon displacement with residual oil saturation to water displacement (Sorw) less than 5%. Rocks with a heterogeneous mix of interparticle and micropores have less favorable displacement, with Sorw as high as 20%, despite having higher permeability. A threshold of approximately 80% microporosity appears to distinguish: (1) more favorable displacement in micropore-dominated rocks vs. less favorable displacement in rocks with a mixed pore system, (2) the magnitude of permeability for a given porosity in mixed vs. micropore systems, and (3) the proportion of microporosity above which pore space of any type is connected exclusively through the micropore network and flow properties reflect the homogeneous nature of that pore system. Within the homogeneous micropore system, Sorw increases from about 5% to 20% as porosity and permeability decrease and micropore type transitions from type 1 (higher quality) to type 2 (lower quality). A major control on multiphase fluid movement in reservoirs with interlayered mixed and micropore-dominated flow units is the contrast in capillary pressure (Pc) and water relative permeability (Krw) between these distinct pore systems. When compared on a consistent basis, 60% water saturation, for instance, rocks with a mixed pore system have approximately neutral (0 psi, 0 kPa) Pc values and higher Krw values, whereas rocks dominated by microporosity have more strongly negative (−6 psi, (−41 kPa) Pc values and lower Krw values. In the case of a water flood operation, this contrast in Pc and Krw can lead to more heterogeneous sweep patterns and lower recovery. A new method for tagging in-place oil with xenon was coupled with flow-through micro-computed tomography imaging to directly investigate oil displacement under water flood conditions. The results provide a qualitative demonstration of how brine flooding displaces xenon-saturated oil. Displacement patterns in micropore-dominated rocks are homogeneous and compact with limited bypass of oil, consistent with relatively low Sorw. Conversely, the displacement pattern in rocks with a mixed pore system is more heterogeneous and exhibits significant regions of bypassed oil, consistent with higher Sorw and Krw.

Abstract: The preservation of the wing membrane of pterosaurs is very poor and the available fossil evidence does not allow its properties to be reconstructed. In contrast, the fossil record for the wing bones is relatively good and the advent of CT scanning has made it possible to build high-fidelity structural models of the wing spar. The bending strength of the wing spar of a 6 m wingspan ornithocheirid pterosaur is used to infer the likely membrane tension. The tensions required to suppress aeroelastic flutter and to minimize ballooning of the membrane under flight loads are also estimated. All three estimates are of similar magnitude and imply that the membrane must have contained high-modulus material, supporting the view that the reinforcing aktinofibrils were keratinous.