The growth of faults and fracture networks in a mechanically evolving, mechanically stratified rock mass: a case study from Spireslack Surface Coal Mine, Scotland

Abstract

Abstract. Fault architecture and fracture network evolution (and resulting bulk hydraulic properties) are highly dependent on the mechanical properties of the rocks at the time the structures developed. This paper investigates the role of mechanical layering and pre-existing structures on the evolution of strike–slip faults and fracture networks. Detailed mapping of exceptionally well exposed fluvial–deltaic lithologies at Spireslack Surface Coal Mine, Scotland, reveals two phases of faulting with an initial sinistral and later dextral sense of shear with ongoing pre-faulting, syn-faulting, and post-faulting joint sets. We find fault zone internal structure depends on whether the fault is self-juxtaposing or cuts multiple lithologies, the presence of shale layers that promote bed-rotation and fault-core lens formation, and the orientation of joints and coal cleats at the time of faulting. During ongoing deformation, cementation of fractures is concentrated where the fracture network is most connected. This leads to the counter-intuitive result that the highest-fracture-density part of the network often has the lowest open fracture connectivity. To evaluate the final bulk hydraulic properties of a deformed rock mass, it is crucial to appreciate the relative timing of deformation events, concurrent or subsequent cementation, and the interlinked effects on overall network connectivity.

Superposed fracture networks

“…Rather than analysing the final fracture network as a single entity (e.g., Zhu et al , 2022), it is necessary to distinguish the different fracture types present and determine the sequence of development of the components of the network (e.g., Katternhorn et al , 2000; Gillespie et al , 2001), if the geometric and topological development of the network is to be understood. This involves using geometric and topological characteristics to define different classes or ages of fracture that are appropriate for the study (e.g., Peacock & Sanderson, 2018; Andrews et al, 2020). Such an approach helps deduce how fractures have been controlled by the interplay between palaeostress fields and earlier structures and would lead to better understanding of the kinematic, tectonic and fluid flow history.…”

The influence of reservoir rock fractures on the efficiency of geotechnical jobs on the Yamal oilfields

“…Table 3 shows that the actual efficiency of hydraulic fracturing operation for one well job is 111.500 tons in Vostochno-Tarkosalinsky oilfield with the high tectonical diversity oil field, while in low tectonical diversity oilfields the actual efficiency doesn't exceed 20.000 tons. In fact, high diversity zones were subjected to stronger different vector diastrophism and as a result, have a more developed fracture network [4]. As for low diversity zones, they were subjected to less tectonical diversity resulting in a less developed fracture network.…”

Drilling into mines for heat: geological synthesis of the UK Geoenergy Observatory in Glasgow and implications for mine water heat resources

“…Outcrops and opencast coal sites exposures highlight the complexity of natural faulting and fracturing in heterolithic Carboniferous successions (e.g. Andrews et al 2020b), strongly influencing groundwater flow (O Dochartaigh et al 2015). Mine plans themselves form a valuable source of fault information (Rippon 1984;Walsh and Watterson 1988;Huggins et al 1995;Monaghan 2017).…”