Browsing by Author "Teodoriu, Catalin"

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    Assessment of deep geothermal energy exploitation methods: The need for novel single-well solutions
    (Elsevier, 2018-06-28) Falcone, Gioia; Liu, Xiaolei; Radido Okech, Roy; Seyidov, Ferid; Teodoriu, Catalin
    Geothermal energy is a constant and independent form of renewable energy and plays a key role towards the world's future energy balance. In particular, deep geothermal resources are largely available across continents and can help countries become less dependent on energy imports and build a broader base in their future energy mix. However, despite its significant potential, the total contribution of the geothermal sector to global power generation remains relatively small. The International Energy Agency has recommended devising plans to address technology-specific challenges to achieve faster growth and improving policies tackling pre-development risks for geothermal energy. Reaching considerable depths is a requirement to exploit deep geothermal resources, but experience gained to date from the implementation of complex, engineered deep geothermal projects has unveiled technical and economic challenges, lower-than-expected performance and poor public image. There is therefore an urgent need for alternative, more sustainable well designs. This paper critically assesses conventional and unconventional deep geothermal well concepts, focusing on the basic Borehole Heat Exchanger (BHE) concept. The discussions are supported by numerical simulations of a BHE design that includes heat conductive fillers to enhance the heat exchange with the surrounding formation, while avoiding direct fluid interaction with the latter.
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    Estimation of plugging and abandonment costs based on different EU regulations with application to geothermal wells
    (Stanford University, Stanford, USA, 2018-02-15) Osundare, Olusegun Samson; Teodoriu, Catalin; Falcone, Gioia; Ichim, Adonis
    This paper presents the cost of plugging and abandonment (P&A) of the Horstberg Z1 well and shows how the well history is considered in the P&A planning process together with existing European regulations. Three different design plans are presented, based on innovative ideas and best practices in the oil and gas industry. Horstberg Z1, located in Germany, was originally a gas well, converted to a scientific geothermal well to prove the single well concept. After serving as a geothermal well for several years, the well has been proposed for P&A. The three designs presented in this work fulfill the purposes of well P&A, and meet the BVOT requirements, which are standard requirements for wells in Lower Saxony, Germany. Following a financial analysis of the designs, it is noted that rig costs are the largest element of the total expenditure, contributing over 50% in the design plans considered. As the number of cement plugs and round trips increase per design plan, the implementation period also increases, which impacts on the total cost. Based on the investigations made in this project, a minimum of USD 1,275,500 is required for the plug and abandonment cost of the well, excluding the well site re-cultivation. A rigless solution for pulling heavy casing out of the wellbore, to avoid the use of a conventional workover rig, would significantly reduce the plug and abandonment cost of the Horstberg Z1 well.
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    Liquid loading in gas wells: From core-scale transient measurements to coupled field-scale simulations
    (Elsevier, 2017-08-12) Liu, Xiaolei; Falcone, Gioia; Teodoriu, Catalin
    Liquid loading is a major operational constraint in mature gas fields around the world. It manifests itself as an increasing back pressure on the reservoir due to a rising liquid column in the well, which initially decreases deliverability, then ultimately causes the gas well to cease production. Theoretically, every gas well will experience this debilitating phenomenon in the latter stages of its producing life. In this paper, both laboratory experiments and numerical simulations are presented to shed more light on the physical process of liquid loading, with a focus on reservoir responses. On the one hand, core-flooding experimental setups of different scales were designed and constructed to investigate back pressure effects on transient flow through the near-wellbore region of the reservoir. On the other hand, the modelling of a gas well undergoing controlled flow and shut-in cycles was performed to validate core-scale observations at reservoir scale, using commercial integrated numerical software that connects a transient wellbore model to a transient reservoir model. The simulated transient characteristics of short-term downhole dynamics (e.g. liquid re-injection and co-current/counter-current flows) supported the U-shaped concept observed in the experiments. The detected temporal distribution of pore fluid pressure within the reservoir medium itself (referred to as the U-shaped pressure profile) was observed both experimentally at the core-scale and numerically at the reservoir-scale. This pressure distribution can be used to explain re-injection of the denser phases into the near-wellbore region of the reservoir.