Feedbacks between faulting and fluid flow throughout the seismic cycle: An experimental approach

In the Earth's crust, fluids are ubiquitous in the pores and cracks present in rocks. In tectonically active areas, for instance along major crustal faults or plate boundaries, rocks deform, crack and fail, which modifies the pore space by either compaction (for instance, collapse of open pores due to grain crushing) or dilation (generation and propagation of new open cracks). These changes in pore space generate local fluid pressure variations and also have a great impact on the ability of fluids to move through rocks and faults. Interestingly, the fluid pressure and fluid flow patterns also have an impact on the deformation of rocks, therefore forming complex feedbacks that determine the overall strength of faults and the long-term tectonics of the Earth's crust. Our understanding of crustal fault mechanics therefore relies crucially on our knowledge of the spatio-temporal distribution of pore pressure in the crust.

Our quantitative understanding of the feedback processes between deformation, fluid pressure and fluid flow in rocks is currently limited by our ability to measure in-situ rock properties, which are required for large scale model predictions. One of the key problem limiting our understanding is that rock deformation and fluid pressure and flow are coupled through large but very local porosity changes occurring prior to, during and after brittle failure.

The goal of the proposed research is, therefore, to unlock this knowledge gap by conducting innovative laboratory experiments that make use of an array of a newly developed type of fluid pressure transducer capable of monitoring local and rapid changes in pressure throughout deformation. By positioning a 3D array of such transducers around laboratory rock samples, we will monitor (1) spatio-temporal localisation of dila- tancy/compaction during quasi-static and dynamic rupture, and (2) the development of heterogeneity and anisotropy in fluid transport properties.

Ultimately, our experimental results will provide the key to the time-evolution of fault zone physical properties that are currently unavailable, but which are essential to fully evaluate the role of pore fluid pressure during deformation and faulting in the crust.

Our project aims at measuring fluid flow and rock physical properties during deformation under crustal conditions, which has the potential to greatly benefit the domain of geoengineering and geomechanics, not only in academic research but also including industry (oil and gas, geothermal, water resources). Possible applications are: (1) practical implementation of our sensor technology in standard industrial tests, (2) benchmarking of reservoir monitoring techniques using laboratory tests, (3) implementation of our 4D permeability mapping for reservoir monitoring, and (4) implementation of our laboratory results to improve hydraulic fracture propagation models.

In the short-term, we will explore the potential applications of our results to industrial problems by directly engaging with practicioners and engineers in the Earth Resources industry. To this end, we have engaged with the applied research organisation TNO (Utrecht offices), which has a branch that specialises in geomechanics, and established an agreement to have the PDRA visit the company for two short stays (one month). During those visits, the PDRA will interact with the team of engineers at TNO to develop the applicability of our results and methods for reservoir monitoring purposes. This exchange will be mutually beneficial since we will have access to the expertise of the TNO staff regarding fluid flow modelling and field data in fractured reservoirs.

In the long-term, our interactions with an applied research and dvelopment organisation like TNO will also be a unique opportunity for the UCL team (PI and PDRA) to develop an understanding of industrial problems, which has a great potential to further collaborations between UCL and industrial partners.

Aside from the academic and industrial impact, we also intend to engage with the general public by using the available communication channels at UCL. UCL has a strong online presence and employ press officers who can efficiently contribute to the dissemination of our work, whenever possible, to the general public. Because our project is at the interface between geology, geophysics and material sciences, we expect that the wide dissemination of our research has a great potential for attracting A-level and undergraduate students in SETM subjects towards Earth Sciences degrees; this will contribute to the training of high-level geophysicists, who are in high demand in industry but recognised to in poor supply from UK universities.