Feasibility study on the management and use of abandoned sites and wells emitting CO2 and CH4 , for the reduction of greenhouse gas emissions

More and more Abandoned Oil and Gas Wells (AOGWs) are being abandoned around the world when the oil or gas fields are considered exhausted or no longer economically viable. Statistics speak of approximately 20-30 million abandoned wells worldwide. The explosion of the shale gas industry is a major reason for this growth in AOGWs. The main endogenous gases emitted by AOGWs are CO2 and CH4. It is estimated that approximately 2.5 million tons of methane are emitted annually from AOGWs. Methane has a global warming potential (GWP) 20-30 times greater than carbon dioxide over a 100-year period and 86 times greater than carbon dioxide over a 20-year period. The increasingly pressing need to remedy the increase in climate change due to anthropic activity has meant that in recent years this problem has acquired more and more weight in the emissions reduction strategies taken into consideration by world governments. An eloquent case is that of the USA, one of the countries most affected by this problem (a quantity of abandoned wells is estimated to exceed 3 million) which has envisaged an investment of $4.7 billion for the mining closure of the same. In fact, at present, the main strategy to reduce GHGs emissions from millions of abandoned oil and gas wells involves the closure of oil&gas fields and mines with concrete caps, although this solution is expensive and above all, at least at the moment, does not guarantee long-term durability time in terms of confinement guarantee. In fact, concrete caps have numerous advantages such as low cost, adequate mechanical, physical and chemical properties compared to the less rigorous and durable materials used before the 1950s. However, the concrete cap solution is also characterized by a number of weaknesses regarding its natural properties, such as the cement during hardening, cracking, mechanical or chemical degradation over time, poor resistance to some endogenous gaseous natural substances such as H2S, CO2 and hydrocarbons as well as instability at high temperatures and pressures. These poor properties negatively affect the integrity of the cement for both the cap and the cement sheath inside the wells, thus forming potential gas-escaping routes for fluid migration and the influx of environmental fluids which accelerate the process of casing contamination and corrosion. Despite innovative cement compounds have been developed to compensate for these weak properties of the cement itself, also this solution is not enough to avoid the endogenous degassing from underground throughout the oil&gas fields as well the geothermal wells too. Various types of fillers or pozzolans have the ability to improve the mechanical strength of cement mixes, as well as properties such as acidic CO2 resistance and low permeability. However, the mechanical and physical behaviour of cement mixes incorporating fillers or pozzolans remains unclear and unpredictable at temperatures above 110°C. At present there isn’t an intelligent system capable of monitoring or collecting passively the GHG gases – energetically available, coming from the abandoned wells, in terms of hardware-software customised devices able to face the chemical-physical properties and the integrity of the wells (i.e. the structural integrity of the well-head closures to be carried out). This means that in many cases, AOGWs as well as recently closed mineral oil & gas wells can suffer the degradation of the cement used for the plugs which, following the overpressure that is growing over the years, should generate cracks and consequent well-degassing progressively higher. In the case of recently closed abandoned oil and gas wells, the issue of well integrity is still present. Even if made recently, the concrete plugs can in fact suffer micro-fractures due, for example, to micro-seismic events or main-shocks close and far with the possibility that the pressurized gas is slowly rising towards the surface, thus generating a new phase of GHGs emissions. At the current time, the lack of a smart system able to intercept, produce and avoid from the atmosphere GHGs as methane means that the national and international databases relating to deep methane, oil, natural gas storage, geothermal wells or more superficial wells characterized by degassing fluids to surface do not present information such as the gases’s emission rate and chemical composition of those gases as well. An exploratory research was therefore carried out with the aim of developing a Smart MonitoringIntercepting Gases System (SMIGS) capable of providing greater information and data on the chemical-physical state of abandoned wells as well as storing/producing to energetic purposes, any gas emitted from the different kind of wells, if economically advantageous. This led to the development of a SMIGS invention that is in the way to be patented by the University of Rome tor Vergata, relating to an experimental prototype, capable of being connected to any abandoned well by analyzing their respective chemical-physical parameters as well as by quantifying GHG-CH4 producible gas in customised thanks or pipelines. As part of the monitoring of both abandoned wells and degassing sites including the possible passive storage/production of gases escaping from them, it will be necessary to power a remote-controlled monitoring hardware that will be installed on remote sites for each well or degassing site chosen. A network of abandoned wells under monitoring/production it will be, in turn, connected to a central station as part of the SMIGS. Many abandoned wells as well as degassing areas in Italy and abroad are very often found in remote areas outside urban areas and they are difficult to be connected by the national electricity grid, therefore requiring the presence of solar or other renewable energy at the remote site. The most suitable system for powering onshore areas without resorting to connection to the national electricity grid is to exploit renewable technologies, in this case photovoltaic systems. This will mean developing a series of small to medium sized photovoltaic power plants near abandoned wells or degassing sites to provide the electrical energy necessary to power this entire SMIGS complex data storage and transmission network. In this context, the problem of the Photovoltaic Heat Island (PVHI) effect is introduced. Electricity production from medium/large-scale photovoltaic (PV) systems has increased exponentially in recent decades. This proliferation of renewable energy portfolios and photovoltaic systems demonstrates an increase in the acceptance and cost-effectiveness of this technology. Corresponding to this surge in installation there has been an increase in the evaluation of the impacts of photovoltaics on various areas. A growing concern that remains under-appreciated is whether or not PV systems cause a "heat island" effect (PVHI) that warms surrounding areas, potentially affecting wildlife habitat, wildland ecosystem function, and health. human and even home values in residential areas. As with the Urban Heat Island (UHI) effect, large PV power plants induce a landscape change that reduces the albedo so that the changed landscape is darker and, therefore, less reflective. The reduction of the Earth's albedo from about 20% in natural deserts to 12% to 5% compared to photovoltaic panels alters the energy balance of absorption, storage and release of short and long wave radiation. The significance of a PVHI effect depends on the energy balance. Incoming solar energy is typically reflected back into the atmosphere or absorbed, stored, and subsequently radiated as latent or sensible heat. Within natural ecosystems, vegetation reduces heat gain and storage in soils by creating surface shading, although the degree of shading varies between plant types. Energy absorbed by vegetation and surface soils can be released as latent heat in the transition from liquid water to water vapor in the atmosphere through evapotranspiration – the combined loss of water from soils (evaporation) and vegetation (transpiration). This heat-dissipating latent energy transfer is dramatically reduced in a typical PV system potentially leading to increased heat absorption by soils in PV systems. This increased absorption, in turn, could increase soil temperatures and lead to a greater influx of sensible heat from the soil in the form of radiation and convection. Furthermore, the surfaces of photovoltaic panels absorb more solar insolation due to the reduction of the albedo. Photovoltaic panels also allow the passage of light energy, which, again, in undrained soils will lead to greater heat absorption. This increased absorption could result in a greater influx of sensible heat from the ground which could be trapped under the photovoltaic panels. The mitigation of a PVHI effect therefore takes on a fundamental role for the development of this technology and its acceptance by public opinion. In this sense, exploratory research was carried out, under the guidance of Prof. A. Spena, aimed at evaluating the thermal behaviour of a photovoltaic panel, mainly at night, starting from a series of climatic conditions to which it is subjected. In particular, the behaviour of the temperatures of the upper surface, the jucntion and back sheet of the panel was analysed, in order to understand the amount of heat emitted by it in the various situations in which it operates. This led to the development of a very reliable mathematical/physical model whose results will be published shortly.