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![Figure 1.6: Dielectric constant values of water, adapted from [31].](profile/Panagiotis-Stathopoulos/publication/322952143/figure/fig1/AS:590956227211264@1517906352303/Dielectric-constant-values-of-water-adapted-from-31_Q320.jpg)
The current thesis concerns the experimental investigation of a novel thermal
drilling technology called hydrothermal spallation drilling. Shallow
spallation drilling applies the impingement of flames on rocks, in order to
break them in small disk-like fragments (spalls), due to the thermal stresses
induced in them. The absence of any contact betwe...
Citations
... However (Xu et al. 2002;Clarke and Profeta 2004), the laser drilling method was never considered feasible for the oil industry. The technique for drilling with a laser would have to cross major obstacles before it could be accepted as a fundamental replacement for rotary drilling methods, but some studies (Xu et al. 2004;Salonitis et al. 2007) show the potential of lasers for drilling, as has been pointed out by research on hydrocarbon, conventional, unconventional, and geothermal reservoirs (Tester et al. 2006;Salonitis et al. 2007;Augustine 2009;Salehi et al. 2009;Teodoriu and Falcone 2009;Teodoriu and Cheuffa 2011;Dall'Acqua et al. 2012;Bazargan et al. 2013aBazargan et al. , 2015Stathopoulos 2013;Kocis et al. 2015). ...
Managed Pressure Drilling (MPD) is a form of drilling which allows greater and more precise wellbore pressure control than conventional drilling also, the mud weight used will be lower than for the conventional mud weight and a secondary choke or frictional pressure will be applied on the surface to create a combined annular pressure profile within the well. In this paper, it was attempted to investigate the effect of high power fiber laser heat tension to carbonate rock body of Kangan formation (K2) during irradiation process with an accurate simulation work and compare the model with experimental results. In commence the enforced stress by heat from the laser source and was analyzed and the fracture propagation pattern in rock body entire irradiation was obtained. This research presented the weakening and fracturing mechanism which generated from heat exposer during laser irradiation and achieved to numerical results for fracture pressure before and after laser irradiation. Also, the MPD as an effective technology to control of this induced anomaly was proposed during Laser-Assisted Drilling (LAD) operation to prevent any loss, gain or hole instability or other drilling problem related to this fracturing and weakening.
... In his doctoral thesis [115], Stathopoulos summarized a number of challenges in practical applications of HSD, including forced ignition, convective heat transfer and water entrainment. According to research needs, ETH has built a pilot platform with a complete measurement and control system, to test the technical solutions against some key problems, explore the scientific issues like the characteristics of HSD, and help verify the simulation results of the actual downhole working conditions. ...
Supercritical hydrothermal combustion, a new and promising homogeneous combustion technology with a wide range of application scenarios and broad development prospects, provides creative ideas and means for the enhanced degradation of organic wastes, hydrothermal spallation drilling, thermal recovery of heavy oil, etc. This technology is elaborated upon in five parts: (1) introducing the main devices including semi-batch reactor and continuous reactor to study the hydrothermal flame in accordance with research institutions, (2) presenting the research status of related numerical simulation from the angles of reaction kinetics and flow-reaction, (3) summarizing the characteristics of hydrothermal flame and combustion by five key parameters, (4) dividing up ignition process and explaining ignition mechanism from the perspectives of critical physical properties of water and heat transfer and mixing conditions, (5) discussing and forecasting its industrial applications including hydrothermal spallation drilling, the thermal recovery of heavy oil, the clean conversion and utilization of coal-based fuel, and the harmless treatment of pollutants. By and large, this paper analyzed in detail everything from experimental equipment to industrial applications, from combustion characteristics to ignition mechanisms, and from summary conclusions to prospect prediction. In the end, herein is summarized a couple of existing paramount scientific and technical obstacles in hydrothermal combustion. Further significant studies in the future should include excellent reactors, advanced monitoring techniques, and powerful computational fluid dynamics.
... The specifications of the vessel designed by Panagiotis S [11] are listed in the following: Normal working pressure ranges from 25 and 40 Mpa. The maximum internal pressure is 65 Mpa for safety reasons. ...
... Combustion chamber in the high pressure vessel[11] ...
... Hydrothermal flame jet in a water bath[11] ...
Geothermal energy has gained more and more attention from all around the globe for its cleanness and efficiency. In the meantime, wells are drilling more and more deeper to develop oil and gas resources. Low rate of penetration is the common problem faced by geothermal wells and deep oil wells. To speed up the development of geothermal energy and petroleum resources in deep formation, a hydrothermal drilling method is proposed here in this paper and the drilling mechanism along with an in-lab experimental setup have been analyzed.
... Eventually, this spall detaches from the rock surface, exposing the newly created rock surface [43,44]. Thermal spallation has shown to be effective and efficient to excavate hard rock materials [44][45][46][47] in great depths [48][49][50]. Therefore, this technology has the potential to outperform currently available technologies for borehole enhancement, which are limited to softer materials and shallower wells [38,40]. ...
... The packer allows the fluids to rise upwards and prevents borehole fluids, situated above the packer, to penetrate into the evacuated zone. This measure results in an air-filled target zone, as entrainment of the high-density aqueous borehole fluids into the lowdensity region of the flame jet, would result in a short, cold exhaust jet with insufficient treatment power [50][51][52]. (3) The burner is ignited and the combustion gases, produced inside the burner, are accelerated through nozzles placed at the lower circumference of the burner unit. The created hot flame jets impinge on the sidewall of the borehole and initiate the thermal spallation process. ...
... Air (2) and methane (3) are mixed at the entrance of the combustion chamber (4). Their combustion is initiated and monitored with an igniter (5), consisting of a heat wire [48][49][50]. In order to maintain the temperature of the burner at an acceptable level, the combustion chamber (6) is cooled by water (7). ...
The creation of deep reservoirs for geothermal energy or oil and gas extraction is impeded by insufficient stimulation. Direction and extension of the created fractures are complex to control and, therefore, large stimulated and interconnected fracture networks are difficult to create. This lack of control and efficiency poses an inherent risk of uneconomic reservoirs, due to insufficient heat-sweep surfaces or hydraulic shortcuts. Therefore, we present a technique, which locally increases the cross section of a borehole by applying a thermal spallation process to the sidewalls of the borehole. By controlled and local enlargement of the well bore diameter, initial fracture sources are created, potentially reducing the injection pressure during hydraulic stimulation, initiating fracture growth, optimizing fracture propagation and increasing the number of accessible preexisting fractures. Consequently, local thermal borehole enlargement reduces project failure risks by providing better control on subsequent stimulation processes. In order to demonstrate the applicability of the suggested technique, we conducted a shallow field test in an underground rock laboratory. Two types of borehole enlargements were created in a 14.5 m deep borehole, indicating the feasibility of the technology to improve the productivity of geothermal, oil and gas reservoirs.
... For these calculations it was assumed that the jet consisted of the products of complete combustion. The resulting jets were modeled as mixtures of perfect gases, while the properties of each gas were calculated after the data of [18] at the flame temperatures (800-1350 • C) presented by Stathopoulos [19]. In the same table we presented the Froude and Grashof numbers for each jet, as a proof that the buoyancy forces could be neglected in almost all the investigated jets. ...
... As we decreased the SOD we observed higher temperatures and larger differences between the thermocouples. Generally, an properties were calculated after [18] at the flame temperatures presented in [19].The buoyancy parameter is presented for an SOD of 15 mm. The nozzle diameter was used as the characteristic length for the calculation of the dimensionless numbers. ...
The current work presents the hydrothermal flame impingement experiments conducted for the design of a hydrothermal spallation drilling nozzle. The products of hydrothermal flames of mixtures of ethanol, water and oxygen were injected as free jets in a high pressure water bath. The nozzle design was based on ideas stemming from underwater welding and cutting of metal sheets. Water entrainment in the flame-jets and the heat transfer capabilities of flames injected from various nozzles have been analyzed by measuring their impingement temperature profiles on a flat stainless steel plate. It was found that the thermal-to-kinetic energy ratio of the jet has a direct influence on the entrainment of water in it. Furthermore, the cooling water of the combustion chamber was injected in various angles to the axis of the jet resulting to different entrainment rates. It was found that higher water injection angles reduced the rate of entrainment. Finally, it was indicated that at certain operational points of the jet, its trans-critical properties had an important influence on the impingement temperatures.
The main costs of developing geothermal processes are concentrated in the project of drilling, accounting for more than 70% of the total budget. Inspired by thermal stimulation technology，a new concept of drilling with liquid nitrogen was presented in this paper. The main objective of this paper is to investigate the effect of rapid cooling on bit-rock interaction and the feasibility of drilling with liquid nitrogen. Through the hardness test experiment results, it showed that the thermal stress caused by rapid cooling can reduce the resistance of indenter invades the rock. Then the micro-bit drilling experiment results indicated that liquid nitrogen can eliminate the thermal damage and enhance the wear resistance, which is the main factor affected the life and footage per bit in geothermal drilling. The negative effect is that liquid nitrogen increase the rock failure resistance slightly and need about 8% more mechanical specific energy compared with drilling with air, but the increase about 8% in mechanical specific energy is affordable to drilling engineers. All these results showed that drilling with liquid nitrogen is beneficial to improve the life and footage per bit, reduce non-production time and reduce drilling costs, it is a promising technology in geothermal engineering.
Thermal cracking of rocks is an intensively studied topic in different research areas and for various engineering problems. In this context, we present a modeling approach which describes thermal spalling of rocks with a focus on thermal spallation drilling. This drilling technology uses high thermal loads to locally destruct the surface of the rock formation. With the presented model, the operating conditions which are required to initiate spalling of rocks can be estimated. Additionally, a Spallability number is introduced allowing a categorization of rocks according to their ability to spall. The presented model is based on linear fracture mechanics and the stress intensity concept. It evaluates if a crack with a certain geometry embedded in a rock with specific properties propagates during exposure to different heat loads and external pressures. Thereby, rapid heat transfer processes are coupled with induced thermal stresses and fracture mechanics in rocks.
The spallation process is based on the effect, that hard rocks with a high quartz content disintegrate into small disc-like fragments, if the rock surface is rapidly exposed to high thermal loads. Spallation is pursued as a contact-free drilling technology for various applications. In view of increasing the knowledge about the process and for determining the limitations of the applicable operating range, a profound knowledge of the minimal required boundary conditions are of significant importance. These conditions are characterized by the lowest surface temperature and heat transfer coefficient at which spallation can be successfully initiated. In order to determine the minimal required boundary conditions, spallation experiments were conducted in which granitic rock samples were rapidly heated by a methane–air burner. A novel measuring concept is proposed to measure the surface temperature, using high-speed pyrometers to temporally resolve the detachment of single spalls. The heat transfer coefficient of the impinging flame was determined by measuring the heat flux in the stagnation point of the jet using an industrial heat flux sensor. The reported data of the boundary conditions show good accordance with data published by other researches and supports their proposed characteristic for the specific heating process.
