The ability to measure the flow rates of fluids in the subsurface is critical if we are to assess and successfully manage aquifers for drinking water, geothermal energy systems, shale gas deposits, and coal gasification projects. Here, it is important to understand the interlinked relationship between fluid flows, permeabilities, and geological structure. This can be attempted through observations made in boreholes. When a borehole is installed, flow up or down the borehole may occur naturally between rock at different depths. The nearby operation of any of the above projects may disturb the fluids in the rock, disrupting the flow in the borehole. If the borehole is used to extract fluids in these engineering applications, then any variability in the flow inside the borehole indicates where the most permeable depths are. Current methods of flow measurement inside boreholes are usually made at a single location. In order to establish what is happening along the entire borehole, a probe must be repeatedly lowered, and another measurement made. This process is tedious, and when the flow is changing over time, it can be impossible to adequately determine how this is happening at all depths. On the other hand, new distributed sensors allow measurements to be made with continuous spatial coverage. Distributed Temperature Sensing (DTS) gives continuous measurements of temperature along fibre optic cables. A fibre optic cable acts as a long (100s of metres to kilometres) thermometer from which temperature measurements can be obtained up to every 12 cm. Such a cable installed in a borehole can give a highly detailed log of temperature along its entire length in just a few seconds. This is useful in itself, but exact quantification of the flows by just passively measuring the temperature is not usually possible. We believe a new method, using heated fibre optic cables and DTS, will be able to measure flow rates. With the proposed method, a cable installed centrally and running to the base of a borehole is heated uniformly by passing a current through the protective materials surrounding the optical fibre. The temperature of the cable, measured using DTS, will increase, and the increase in temperature should depend on how fast the fluid is flowing past it. Faster flows should remove heat more efficiently, lowering the cable temperature. Such a system would potentially be able to measure flows every 12 cm, and be able to detect changes occurring in the flow every few seconds. The method will be tested in a controlled way using a borehole constructed in a lab from PVC tubing. This would allow access inside and allow us to visually inspect the flow (using dyes) and equipment during testing. A prototype heated 'Active' DTS (A-DTS) system is to be installed in the tube. From a storage tank, water will be pumped through the tube at varying rates, mimicking flow inside a borehole. This will allow is to determine how the temperature of the cable changes in different flow conditions. We will then adjust the heating power of the cable, as the temperature changes due to different flows may be more readily detectable when using higher or lower powers. Finally, the temperature effect at inflow/outflow locations (as would happen where a rock is fractured) will be investigated using inflow/outflow ports in the centre of the artificial borehole. The exact set-ups and the underlying physics will be tested using advanced numerical model techniques.

We propose the development of a novel, distributed soil moisture and temperature monitoring network that will present a step change from currently available monitoring technologies, which tend to be based on data collection at isolated points in time and space, to real-time, spatially-distributed data collection that enable effective and responsive decision making to deal with rapidly increasing demands in a changing climate. The proposed system will be based on combining Distributed Temperature Sensor (DTS) technology with an active heat source. The so-called Active DTS (A-DTS) allows observing flow-related heating and cooling patterns along the actively heated cable. It is this Distributed Heat Pulse, A-DTS technology that we will use in the development of the proposed Sensor network - DiHPS. While broader applications in heat and water flux assessments will be possible with DiHPS, in this project we will focus on demonstrating its suitability to quantify the moisture content and thermal properties of the soil. Description of the spatial and temporal distribution/ dynamics of these soil parameters is important for many agricultural, engineering and meteorological applications. Soil moisture, for example, is a key state variable in controlling land-atmosphere interactions and an early indicator of changes in the hydrological system, e.g. associated with daily evapotranspiration or event-based recharge cycles or with extreme events (i.e., droughts or floods). It is widely used in agriculture (e.g., irrigation management), forestry (e.g. plantation water demand estimations), meteorology (e.g. local and regional weather forecasts), water resources management (e.g. estimation of groundwater recharge) as well as a state indicator variable in drought / flood early warning systems. Soil thermal properties influence the partitioning of energy within the ground and at the ground surface, and are related to soil temperature and the movement of heat and water within the ground and their transfer across the ground surface. For these reasons, soil physicists, crop scientists and micrometeorologists study thermal properties, and they are also important in engineering applications, (e.g., determining the electric current rating of buried cables, ground heat exchanger design). We will build on earlier work which has demonstrated the principal capacity of A-DTS to measure soil moisture under controlled conditions in a lysimeter facility. We will expand this technology from a single point application to a distributed, real time sensor network and a coiled, vertical A-DTS profiler for measuring soil moisture content and thermal properties at high spatial and temporal resolution. The network and profiler will be tested at TRL4 by installing it at our test site at the Birmingham Institute for Forestry Research (BIFoR). The results will be compared with in-situ soil moisture content and thermal property data from Frequency-Domain Reflectometry (FDR) soil moisture probes and thermal needle probe measurements, respectively. To achieve real-time, autonomous system operation, a set of heating strategies will be tested and initial threshold (trigger values) will be defined. These will define at what change in soil temperature, as observed by continuous temperature observation in DTS passive mode, initiation/cessation of the DTS active mode will be triggered. A key component of DiHPS is the real-time control for triggering the change from active to passive observation mode. This will require the development of a set of algorithms, based on inverse modelling and asymptotic approaches, which can process the raw DTS data in real-time to provide the required outputs. No existing DTS-application attempts to provide temperature or soil moisture data temperature in such detail and in real-time. If successful, we anticipate a step change in the way DTS is employed, e.g. in early warning systems or for providing detailed process understanding.

Our cities are criss-crossed with fibre-optic telecommunications networks. For system redundancy and after technological improvements have reduced the required bandwidth, much of the installed fibre is unused. This unused fibre is known as "dark fibre". We can use dark fibre to investigate the properties of the ground below our cities. Distributed Acoustic Sensing (DAS) systems fire laser pulses along fibre-optic cables, and record the back-scattered light. If the cable is stretched or compressed then the back-scattered light will arrive slightly later or earlier. By recording and mapping these changes, we can turn any fibre-optic cable into a geophysical sensor, recording any movements or vibrations along the cable with very high resolution. Seismic imaging is a well-established method to map the subsurface. The technique uses seismic sources such as a hammer strike or a special vibrating source to impart seismic energy into the ground. By recording the resulting vibrations that have reflected and/or refracted through the ground, we can build up an image of the subsurface. These images are useful for a broad range of applications, such as siting geothermal developments, understanding groundwater and drainage, assessing the likelihood of landslips, and detecting sinkholes. However, conventional seismic surveys rely on deploying a large array of geophone sensors across the survey area. This is often logistically challenging or impossible in urban areas. As a result, subsurface data under our towns and cities, perhaps the area where this data is needed most, is often lacking. Seismic imaging using DAS provides an alternative with enormous potential. Dark fibre cables are already installed in buried telecommunication networks, meaning our sensor is already in place and available at minimal cost. We can access the fibre-optic network, install a DAS unit in a secure location, and record the resulting seismic data along the length of the cables, without any need to deploy geophone sensors across the area of interest. Hence, DAS seismic acquisition using dark fibre offers the potential to transform how we acquire images of the subsurface in urban areas. To date, the enormous potential of this method is only just being realised. The objective of our research is to investigate the performance of dark fibre DAS for seismic imaging in urban settings, with the aim of working out how best to acquire and process this type of data. We will acquire data using the B-NET telecommunications network, which is a 250 km-long fibre-optic network running across the city of Bristol (owned by Bristol City Council). We will use this data to identify how to produce the best quality DAS seismic images - for example what types of seismic source are best, how best to set up the DAS acquisition unit, and how best to process the resulting data. One of the major challenges of DAS seismic acquisition in urban areas is that background noise levels are likely to be high. This background noise could degrade the quality of our imaging. To address this, we will develop the use of state-of-the-art artificial intelligence algorithms to remove the background noise, improving the quality of our resulting images. All of the data that we acquire and all of the machine learning algorithms that we develop will be posted to publicly available repositories. This will provide an extremely valuable resource for researchers and commercial geophysical companies, both in the UK and globally, who are working on the development of this technology.

Microseismic monitoring during hydraulic stimulation allows operators to monitor the development of fractures as they propagate. They can then optimise their operations, while ensuring that they are conducted in an environmentally safe manner. Presently, microseismicity is monitored either using geophones placed in dedicated monitoring boreholes, or dense sensor arrays at the surface. These methods are costly, and can pose logistical challenges. In certain settings, monitoring is also limited by the performance of geophones at high temperatures and pressures. As a result, microseismic monitoring arrays are typically deployed for less than 25% of fracturing operations in North America. Improvements in microseismic monitoring systems are needed, allowing operators to deploy effective microseismic arrays at most (or all) hydraulic fracturing sites in an economically and logistically viable manner. This will enable them to optimise hydrocarbon extraction at these sites, while ensuring that they operate in an environmentally-responsible manner. In-well deployment of fibre-optic cabling as a Distributed Acoustic Sensor (DAS) addresses the cost and logistical problems outlined above and has shown significant potential as a microseismic monitoring tool. The use of fibre-optic DAS in this context requires the development of novel data processing algorithms capable of handling this new type of data. This project will develop bespoke DAS instrumentation workflows, to be used by oil and gas companies and microseismic service companies. Chevron, one of the world's largest multinational oil and gas companies, regularly conduct hydraulic stimulation activities and they are exploring the use of fibre-optic DAS as a microseismic monitoring tool. Use of the novel processing workflows developed during this project will enable Chevron to increase the uptake of fibre-optic as a microseismic monitoring tool amongst their operational divisions. Shale gas operators must submit a Hydraulic Fracturing Plan (HFP) to the Environment Agency (EA) and Oil and Gas Authority (OGA) for approval before hydraulic fracturing can take place. The EA strongly recommends the use of microseismic monitoring to map the growth of fractures during stimulation. To ensure regulatory compliance, the EA must therefore develop the capacity to efficiently evaluate microseismic monitoring plans submitted to the agency. Since an HFP will include a proposal to monitor for seismic events, regulators require up-to-date knowledge in this rapidly developing field to assess material submitted to them by the operators. Through close collaboration, this project will allow the EA to determine whether proposed microseismic deployments, including fibre-optic monitoring, satisfy regulatory requirements. The main project of objectives are to: 1. Develop processing workflows for fibre-optic DAS data through partnerships with the full supply chain from equipment supplier (Silixa), to data processing, to end-user (Chevron). 2. Develop tools and guidelines for regulators for the assessment of microseismic monitoring plans including DAS technology for hydraulic fracturing in the UK. These objectives will be achieved by through three work packages. 1. Microseismic processing workflows currently used to treat geophone data will be adapted for application to DAS fibre-optic data. 2. The processing workflows will be optimised for use with large data volumes because any fit-for-purpose processing method must be capable of handling large data volumes. 3. Embed new knowledge in the regulators of the shale gas industry in the UK through a workshop, development of tools for inclusion in their processes and a short-term placement at the EA. With the first UK shale gas sites due to begin hydraulic fracturing this year, this project is particularly timely and important for the future success of the UK shale gas industry, with significant potential worth to the UK's economy.

The DiSTANS project will use state-of-the-art technology to provide a brand-new method of monitoring changes underground. This offers the possibility of game-changing data capture to examine subsurface processes. This method uses fibre optic cables similar to those used in telecommunications, to get data from underground at a speed and density that far exceeds traditional monitoring technology. The optical fibres in the cables have small imperfections in them. The new technology shoots a pulse of light along the fibres, which reflects off the imperfections and returns to the recorder. The tiny differences in the time that the light takes to return will tell us about very small vibrations, temperature changes and movements around the underground cable. Because the cable is the sensor, we can monitor the underground conditions for up to 15 km and see differences along the cable as close together as 25 cm. These measurements are taken one hundred thousand times each second, which means that very quick changes can also be measured. This new technology, called distributed strain, temperature and acoustic sensing suite, can be used in many different places. It can be used to monitor volcanoes and earthquakes, but can also be used to keep track of traffic and people walking. For the first project, we will be installing the DiSTANS system on the North Norfolk coast, where the sea erodes the coast at a rate of 10 cm per year, threatening people's houses and businesses, and posing a danger for people and wildlife who use the coast. We will monitor small cracking and slumping before landslides, and how these are affected by temperature changes each day and season.