Hydrothermal Spallation Drilling Research Articles

Review on an Advanced Combustion Technology: Supercritical Hydrothermal Combustion

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.

Experiment investigation of granite damage under the high-temperature and high-pressure supercritical water condition

Geothermal energy has the potential to produce significant amounts of electricity. Hot dry rock, stored abundant geothermal energy, is mainly made up of granite and hard to drill. Hydrothermal spallation drilling (HSD) is suitable to drill in hard granite formation. The granite breakage in HSD means the granite is induced to spall under high-temperature and high-pressure supercritical water condition, which is a key problem in HSD application. In this paper, we investigated the effect of supercritical water on granite damage by experiment. First, the granite samples were heated under the supercritical water condition. Meanwhile, another granite samples were also heated by air for comparison. After that, abundant post processing tests were conducted to compare the three type of granite samples: samples heated by supercritical water, samples heated by air and original samples. Specifically, the mineral analysis, uniaxial tensile test, uniaxial compression test, acoustic wave test was conducted to quantitatively investigate the granite damage. Meanwhile, thin section observation and scanning electron microscope observation were conducted to investigate the fracture distribution in the samples after damage. This study can provide useful insight into the granite damage heated by supercritical water, which can help to optimize the design of HSD in field application.

Hot surface ignition and monitoring of an internal oxygen–ethanol hydrothermal flame at 260 bar

In this work a custom made sensor with an extended service life at temperatures up to 900°C and able to sustain intermittent temperatures in excess of 1000°C is used to ignite and monitor a hydrothermal combustion at 260bar. Once calibrated, the sensor features a mean sensitivity of 27μV/°C and an absolute systematic uncertainty of ±10°C with 95% confidence from room temperature to 1000°C. After ignition, the influence of the fuel injection geometry, the equivalence ratio and the fuel mass flow on the internal temperature profile are investigated and in the end, applications of the proprietary sensor in supercritical water oxidation and hydrothermal spallation drilling are highlighted.

“Stagnation flow heat transfer of confined, impinging hot water jets under supercritical pressures”

Hydrothermal spallation drilling is a possible alternative drilling technology based on the characteristics of certain rock types to disintegrate continuously into small fragments when exposed to high thermal loads. Impinging supercritical water jets or hydrothermal flames are favored to provide the required heat for thermal fragmentation.Hence, stagnation flow heat transfer under supercritical pressures of water was investigated by means of two calorimetric sensor devices covering a wide range of heat fluxes and surface temperatures. A numerical model based on ANSYS FLUENT was established to predict the heat transfer in conjunction with the Shear-Stress Transport k–ω turbulence model and the REFPROP database to calculate the thermo-physical properties. Finally, area-averaged heat transfer coefficients in the stagnation region of impinging hot water jets were determined by numerical simulations and validated against experimental measurements. Generally, the experimental trends were predicted correctly by the numerical model although the absolute heat transfer was overestimated.

Hot surface ignition of oxygen–ethanol hydrothermal flames

In this work we present the hot surface ignition of turbulent diffusion oxygen–ethanol hydrothermal flames. For this purpose up to 520W electric are dissipated through a heating wire. The mean wire temperature and the electrical energy it releases at ignition are reported by measuring the voltage drop across its resistance. The wire temperatures – up to 385°C – are compared to the auto-ignition temperatures reported in literature and the ignition map of our system is drawn. In case the reactants are injected at room temperature, the hot surface enables ignition for ethanol contents in the aqueous fuel stream above 30wt.%. In the end, potential applications of the ignition system in the scope of supercritical water oxidation and hydrothermal spallation drilling are highlighted.

Simulating Supercritical Water Jets with a Variable Turbulent Prandtl Number

AbstractSupercritical water jets are of interest for the hydrothermal spallation drilling technology to thermally fragment rock. The important thermal field of such jets was investigated via axial temperature measurements inside a high‐pressure vessel simulating the harsh pressure and temperature conditions found downhole. Deionized water was electrically preheated to supercritical temperatures and afterwards discharged into a slowly co‐flowing cooling water ring. Furthermore, a numerical model was developed and applied. Difficulties in simulating the thermal field due to the strongly varying fluid properties around the pseudo‐critical point of water were highlighted and critically discussed. An approach of a locally varying turbulent Prandtl number is introduced to improve the predictions compared to the experiment. Finally, all numerical results were validated with experimental data.

Numerical analysis of penetration lengths in submerged supercritical water jets

“Hydrothermal spallation drilling” is a possible alternative drilling technology that uses the properties of certain rock types to disintegrate into small fragments when heated up rapidly by a hot impinging fluid jet. Hot supercritical water jets are favored to provide the required heat for thermal rock fragmentation. However, the indispensable presence of a dense water-based drilling fluid during operation can cause considerable heat losses in the supercritical water jet before impingement on the rock surface. To predict these heat losses from the hot jet to the cold aqueous environment, a numerical model based on the commercial CFD tool ANSYS FLUENT® was established. Penetration lengths of the supercritical jet plume at near-critical pressures were determined numerically and validated with experimental values for a wide range of conditions. Experiments and simulations showed an acceptable agreement and the experimental trends were satisfactorily predicted by the model.

Development of a calorimeter for heat flux measurements in impinging near-critical water jets confined by an annular wall

One approach in hydrothermal spallation drilling is the use of hot, impinging, supercritical water jets to induce rock fragmentation. The heat transfer from hot jets to the rock's surface is of major interest for the drilling process. This work therefore presents heat flux measurements in the challenging environment of confined supercritical water jets impinging on a flat surface. A sensor based on the calorimetric measurement principle and the according experimental methods were developed to determine heat transfer coefficients of subcritical and supercritical water jets. In the subcritical temperature range the results show good agreement with existing empirical correlations originally developed for isothermal, subcritical, liquid jets. An interesting behavior was though observed for supercritical injection temperatures: when the impinged surface is still at subcritical temperatures, the peak of the water's specific heat at the pseudo-critical temperature dominates the heat transfer even at injection temperatures far beyond the pseudo-critical temperature.

Heat transfer of supercritical mixtures of water, ethanol and nitrogen in a bluff body annular flow

Hydrothermal spallation drilling is a promising drilling technique that could prove economically advantageous over rotary techniques for deep wells, where hydrothermal flames can provide the required heat to spall the rock. Assisted ignition of hydrothermal flames must be understood prior to the field implementation of the technology. The convective heat transfer in a burner setup has been therefore investigated, where the flow conditions are similar to those of a bluff body wake flow in annular geometry. Various ternary mixtures of water, ethanol and nitrogen were used as model working fluids to simulate the combustion conditions of water–ethanol mixtures with oxygen. Water ethanol mixtures were pre-heated between 350°C and 420°C, and nitrogen was pre-heated up to 400°C, while the working pressure was set at 260bar. The convective heat transfer coefficient from an electrically heated surface to the mixtures is presented.

Calibration of a Gardon Sensor in a High-Temperature High Heat Flux Stagnation Facility

A calibration methodology developed for custom-made heat flux sensors used for the investigation of hydrothermal spallation drilling is presented. An air jet stagnation convection calibration system allowing independent control of jet velocity and temperature, cooling water flow and temperature, stand off distance, and nozzle diameter was built. A thermopile device was used as reference heat flux sensor. Air jets with velocities up to 400 m/s, exit temperatures of 760°C, and heat fluxes up to 0.6 MW/m2 can be reached. The standard deviation of a reference heat flux measurement is below 2%, and overall uncertainty achieved is less than 5.5%.