Supercritical Carbon Dioxide Jet Research Articles

Impact frequency variation of self-excited oscillation pulsed supercritical carbon dioxide jets

In order to obtain the impact frequency of resonant coal breaking by self-excited oscillation pulsed supercritical carbon dioxide (SC-CO2) jet, large eddy simulation was used to analyze the formation and development process of self-excited oscillation pulsed SC-CO2 jet, the variation of jet impact frequency in the nozzle and the free flow field, and the variation of jet impact frequency at different positions in the jet axis and under different cavity lengths. The test device of jet impact frequency was developed, and experiments were performed to verify the conclusions of the numerical simulations. The results show that the frequency of the self-excited oscillation pulsed SC-CO2 jet is different in the nozzle and the free flow field. In the nozzle, the frequency generated by the fluid disturbance is the same, and the jet frequency at the exit of the nozzle is consistent with that inside the nozzle. In the free flow field, due to the compressibility of CO2, the pressure, velocity and other parameters of SC-CO2 jets have obvious fluctuation patterns. This feature causes the impact frequency of the self-excited oscillation pulsed SC-CO2 jet to decrease gradually in the axis. Changing the cavity length allows the adjustment of the jet impact frequency in the free flow field by affecting the disturbance frequency of the self-excited oscillation pulsed SC-CO2 jet inside the nozzle.

Simulation study of supercritical carbon dioxide jet fracturing for carbonate geothermal reservoir based on fluid-thermo-mechanical coupling model

Geothermal energy is a kind of renewable, sustainable and clean energy resource. Geothermal energy is abundant in carbonate reservoirs. However, low matrix permeability limits its exploitation. The supercritical carbon dioxide (SC–CO2) jet fracturing is expected to efficiently stimulate the carbonate geothermal reservoirs and achieve the storage of CO2 simultaneously. In this paper, we established a transient seepage and fluid-thermo-mechanical coupled model to analyze the impact performance of SC-CO2 jet fracturing. The mesh-based parallel code coupling interface was employed to couple the fluid and solid domains by exchanging the data through the mesh interface. The physical properties change of SC-CO2 with temperature were considered in the numerical model. Results showed that SC-CO2 jet fracturing is superior to water-jet fracturing with respect to jetting velocity, particle trajectory and penetrability. Besides, stress distribution on the carbonate rock showed that the tensile and shear failure would more easily occur by SC-CO2 jet than that by water jet. Moreover, pressure and temperature control the jet field and seepage field of SC-CO2 simultaneously. Increasing the jet temperature can effectively enhance the impingement effect and seepage process by decreasing the viscosity and density of SC-CO2. The key findings are expected to provide a theoretical basis and design reference for applying SC-CO2 jet fracturing in carbonate geothermal reservoirs.

Application of supercritical carbon dioxide jet to recycle waste tire rubber: An experimental and optimization study

Towards devising an efficient recycling technology concerning both rubber pulverization and devulcanization, this study employed supercritical carbon dioxide (ScCO2) jet for recycling waste tires. The particle size and devulcanization extent of the resulting ground tire rubber (GTR) were monitored at different processing conditions, which were optimized by adopting a response surface methodology. The use of ScCO2 jet led to fine GTR with irregular surfaces, with a sufficient pulverization of rubber observed at a high jet pressure. A higher temperature led to a high degree of devulcanization and an improved breakage selectivity of crosslinks. Moreover, it was found that an ambient pressure would not enhance rubber pulverization nor devulcanization; however, it was necessary to maintain the supercritical state of carbon dioxide. Upon optimization, the radical reactions between broken polymer chains or sulfur crosslinks led to a GTR devulcanization degree of approximately 45 %, registering a final particle size of 0.162 mm.

Cavitation stripping of graphene by circulating supercritical carbon dioxide jet and its properties

In this paper, graphene was stripped by circulating liquid phase method, supercritical carbon dioxide was selected as stripping agent, and a cavitation device was set on the pipeline to generate supercritical carbon dioxide jet cavitation to strengthen graphene stripping. Using the characteristics of small molecule intercalation and easy separation of scCO2, we succeeded in stripping graphene with fewer layers. With pressure of 10–16 MPa, temperature of 40 °C, time of 1 h, supercritical carbon dioxide circulation flow of 12 L/h, 0.47 mg/ml graphene dispersion can be obtained. Through electron microscope characterization, it can be judged that its ID/IG value was only 0.167, and the proportion of double-layer graphene reached 65%. Using the obtained dispersion to prepare flexible films, graphene films with resistivity of 0.0239 Ω /m, sensitivity of 176 and stable performance after 1000 cycles can be obtained. The advantage of this method was to avoid using expensive organic solvents such as NMP. After jet cavitation strengthening, the efficiency was higher and the conditions were milder than that of the simple supercritical carbon dioxide stripping method, which was conducive to the realization of industrial application.

Propagation Characteristics of Fractures Induced by Supercritical Carbon Dioxide Jet in Hard and Soft Layered Rocks

The initiation and propagation behavior of fractures induced by supercritical carbon dioxide (SC-CO2) jet fracturing is significant to evaluate stimulated reservoir volume (SRV). However, the propagation characteristics of fractures induced by SC-CO2 jet in layered rocks with layers having different mechanical properties have not yet been studied. In this study, four groups of artificial sandstones were used to conduct SC-CO2 jet fracturing experiments and investigate the fracture initiation and propagation behavior in hard and soft layered rocks. A strain collection device was employed to monitor the strain changes of the specimens during the experiments, and after the experiments, a three-dimensional scanner was used to obtain the morphologies of the main fractures. Experimental results showed that the SC-CO2 jet fracturing can be divided into the pressurization of the perforation pressure stage and fracture propagation stage, and the fractures initiation and propagation is intermittent. Three types of main fractures have been found—longitudinal fracture, transverse fracture and oblique fracture—and the formation mechanism of the main fractures has been elaborated. The rock strength can affect the number and complexity of fractures created and the fracturing rate, and the Young’s modulus of rock has an effect on fracture propagation length. The fractures mainly develop near the perforation and are difficult to propagate to another layer with different mechanical properties. The result in our study is conducive to the application of SC-CO2 jet fracturing technology in the field.

Investigation on the fluctuation characteristics and its influence on impact force of supercritical carbon dioxide jet

Supercritical carbon dioxide (CO2) jet-assisted drilling is considered a promising technology in unconventional natural gas drilling engineering. The flow field characteristics of the supercritical CO2 jet are the critical factors that affect the erosion performance of the jet. The relation between the flow fluctuation characteristics and the jet is required further investigation to enhance its erosion performance. In this study, the fluctuation features of a supercritical CO2 jet were simulated based on a modified real gas model. Subsequently, impact force tests were conducted using an I-Scan flexible array pressure sensor to obtain peak pressures at different standoff distances. The results indicated that the flow field structure of the supercritical CO2 jet exhibits typical compressible wave-like features, which can be accurately determined by the expansion ratio. The expansion ratio was mainly affected by the inlet pressure, inlet temperature, and ambient pressure. The static pressure, temperature, and velocity distributions of a free jet could be significantly influenced by the fluctuation characteristics. Among them, the static pressure and temperature trend decrease in the expansion waves and increase in the compression waves, while the velocity shows a contrary variation trend. When the jet was under-expansion, the lengths of the wave node and jet potential core increased with increasing inlet pressure and decreased with increasing inlet temperature and ambient pressure. Moreover, the fluctuation characteristics of the flow field significantly affected the peak impact force of the supercritical CO2 jet. The peak impact force at the compression wave positions tended to be higher than that at the adjacent expansion wave positions. The maximum pressure difference of jet impact was 7.39 MPa in this study, which occurred when the standoff distance was 23.0 and 17.3 mm and accounts for 18.6% of the impact pressure at 23.0 mm. A plate shock wave was observed ahead of the target when the standoff distance was larger than 23.0 mm, which accounted for the abrupt decrease in pressure at the stagnation region.

High-quality ground tire rubber production from scrap tires by using supercritical carbon dioxide jet pulverization assisted with diphenyl disulfide

This study presents a high-quality ground tire rubber (GTR) production technology by using supercritical carbon dioxide jet pulverization. Diphenyl disulfide was incorporated as the devulcanization reagent during the pulverization process. The effects of rubber swelling on particle size distributions, shape characteristics, thermal degradation behaviors, and devulcanization behaviors of the acquired GTR were investigated. The results showed that fine pulverization of scrap tires can be achieved, along with a desired degree of rubber devulcanization. Rubber swelling or devulcanization was associated with the failure pattern of rubber under jet impact and was not beneficial for fine pulverization. Rubber devulcanization mechanisms included radical and oxidation-based reactions, both of which showed breakage selectivity of crosslinks. The excellent properties of the acquired GTR can help to achieve good dispersion and enhanced interfacial compatibility with the polymeric matrix. Therefore, supercritical carbon dioxide jet pulverization incorporated with diphenyl disulfide is a promising recycling technology for scrap tires.

Heat-fluid-solid coupling mechanism of supercritical carbon dioxide jet in rock-breaking

Aiming at the synergistic rock-breaking mechanism of supercritical carbon dioxide (SC-CO2) jet pressure and temperature difference, a heat-fluid-solid calculation model of rock-breaking stress was established and verified to be effective, and the variations of jet flow field and rock stress with jet standoff distance of SC-CO2, water and nitrogen were studied. With the increase of jet standoff distance, the jet pressure of SC-CO2 decreases and the jet temperature difference increases. The SC-CO2 jet is higher in pressure than the nitrogen jet and differs little from the water jet. Temperature difference of SC-CO2 jet is 5 times that of water jet and more than 2.5 times that of nitrogen jet when the jet standoff distance is larger than 10. The temperature stress is the main reason why SC-CO2 jet is superior to water and nitrogen jets in rock-breaking. The rock under the SC-CO2 jet has greater rock stress, effective rock-breaking jet standoff distance and rock-breaking area. The jet pressure plays a major role in rock-breaking when the jet standoff distance is small, while the jet temperature difference plays a major role in rock-breaking when the jet standoff distance is large. The SC-CO2 jet is an efficient volume rock-breaking method, which results in tensile and shear failure on the rock surface under short time jet and large area tensile failure inside the rock simultaneously under long time jet.

Application of supercritical carbon dioxide jet: A parametric study using numerical simulation model

Defining the structure of a supercritical carbon dioxide (SC–CO2) jet flow field is a critical component of establishing a theoretical basis for its application. This study investigates the influence of pressure ratio on the wave features of an SC-CO2 jet flow field using a new numerical simulation model and flow field visualization experiments. To assess the characteristics of the SC-CO2 flow field and predict the distribution of temperature and pressure, a computational model based on constant pressure specific heat capacity and thermal conductivity of SC-CO2 was established, and the user-defined function (UDF) feature available in ANSYS Fluent software was used. The results demonstrated that the temperature and pressure of the SC-CO2 jet flow field could be accurately predicted by the numerical simulation model proposed in this research, and the wave features of the flow field could be visualized by both the numerical simulation contours and the experiments. The wave features, which resulted from different pressure ratios, were found be a function of the structure of the Laval nozzle at a constant inlet pressure. The pressure ratio could be controlled by the nozzle structure and accurately describe the wave features of the SC-CO2 jet flow field. In this study, an optimal pressure ratio of 1.31 was used and the flow field structure corresponding to the maximum jet impact force could be satisfactorily described by the optimal pressure ratio.

Study on the Impact Pressure of Swirling-Round Supercritical CO2 Jet Flow and Its Influencing Factors

Supercritical carbon dioxide (SC-CO2) jet is capable of decreasing the threshold pressure of rock breakage and mitigating formation damage, owing to its low viscosity, high diffusivity, and extremely-low surface tension. The swirling-round jet holds the advantages of both a swirling jet and a round jet. Therefore, the comprehensive technique, swirling-round SC-CO2 (SR-SC-CO2) jet, is expected to substantially enhance rock-breaking efficiency. However, theoretical analysis of the flow field characteristics of SR-SC-CO2 has not been reported yet. This work aims to lay a theoretical foundation for employing SR-SC-CO2 in drilling and fracturing. The flow field is simulated using Naiver-Stokes equations and the RNG k-ε turbulence model. Sensitivity analysis, regarding pressure drop of the nozzle, confining pressure, fluid temperature, jetting distance, the diameter of the nozzle’s central hole, and grooving area, are performed. We show that the combined swirling-round SC-CO2 jet flow could maintain a relatively larger axial as well as tangential velocity compared to a single approach of swirling jet or round jet, enabling one to acquire a deeper oillet and expand the perforation area effectively. The simulation results substantiate the enormous potential of SR-SC-CO2 in improving rock-breaking efficiency and clarify the influence of relevant parameters on the impact pressure of the jet flow.

Effect of nozzle structure on coal breakage of SC-CO2 used for well drilling

Supercritical carbon dioxide (SC-CO2) jet is a promising technology for the extraction of coalbed methane. As a key component in the process of jet formation, the nozzle is an essential factor affecting the efficiency with which an SC-CO2 jet breaks coal and rock. The nozzle structure directly affects the energy conversion rate and flow field structure of the jet. Thus, the use of a suitable nozzle can maximize SC-CO2 energy utilization, reducing energy loss and engineering costs while achieving energy conservation and emission reduction. Based on the conical convergent nozzle and the Laval nozzles, this study conducted an SC-CO2 jet coal breakage experiment and an I-Scan pressure testing experiment using experimental research methods. The influence of nozzle structure on SC-CO2 jet coal breakage was studied and the results indicate that when the inlet pressure is constant, the Laval nozzle has a higher energy conversion rate and a stronger coal breakage effect than the conical convergent nozzle. Furthermore, considering the combined effects of the energy conversion rates of Laval nozzles and energy dissipation under ambient pressure, a key parameter for assessing Laval nozzles was discovered: the expansion ratio. The results indicate that the impact of jet temperature on the expansion ratio is small and that increasing the erosion effect of an SC-CO2 jet by increasing the jet temperature is an energy-consuming and inefficient method. Essentially, the optimum coal breakage effect of the SC-CO2 jet is obtained when the expansion ratio of the Laval nozzle is between 1.07 and 1.29.

Preparation of devulcanized ground tire rubber with supercritical carbon dioxide jet pulverization

This work presents a novel waste tire rubber reclamation method using supercritical carbon dioxide (ScCO2) jet pulverization. The particle size distributions of the acquired ground tire rubber were analyzed and the rubber devulcanization behaviors were investigated. Results show that devulcanized ground tire rubber with fine particle size and coarse surfaces can be acquired in ScCO2 jet pulverization. The rubber swelling in ScCO2 significantly impedes fine pulverization. The jet impact mainly results in main chain scission, while long reaction time and low jet pressure are beneficial for the selective breakage of crosslinks. It indicates that ScCO2 jet pulverization can be an excellent choice for WTR reclamation concerning both size reduction and rubber devulcanization.

The effect of shale bedding on supercritical CO2 jet fracturing: A experimental study

The bedding plane of shale is related to anisotropic mechanical property, which apparently affects the shale fracturing. To investigate the influence of shale bedding on the fracture morphology and perforation damage under Supercritical Carbon Dioxide (SC–CO2) jet fracturing, the experiments were comprehensively studied via the macro fracture analysis, strain monitoring, Scanning Electron Microscope (SEM) test and Energy Dispersive Spectroscopy (EDS) test. The results demonstrated that the average Young's Modulus (YM) and Uniaxial Compressive Strength (UCS) of shale specimen with the bedding plane angle of 0° is 9.37 times and 2.89 times of the shale specimen with bedding plane angle of 90°, respectively. During jet fracturing, both the jet pressure and existing bedding are beneficial for fracture initiating and propagating naturally along the weak bedding planes, and shear fracture can enhance the fracture complexity. When the perforation distributes in the direction perpendicular to the bedding plane, the less strain can be obtained, and the mass loss and CO2 absorption of shale specimen significantly increase by 350% and 300%, respectively, as the jet pressure increases from 25 MPa to 50 MPa, which is larger than the shale specimen with bedding plane angle of 0°. The perforation damage is explored after jet fracturing via SEM and EDS, and it is found the direction of perforation perpendicular to the bedding plane is beneficial for micro-cracks generation, and leads to 10% decline of carbon (C) and oxygen (O) elements in the samples. These studies clearly show the influence of the bedding plane angle on the fracture morphology and perforation damage, which are crucial for SC-CO2 fracturing and CO2 storage in shale reservoir.

The Flow Characteristics of Supercritical Carbon Dioxide (SC-CO2) Jet Fracturing in Limited Perforation Scenarios

Supercritical carbon dioxide (SC-CO2) jet fracturing is a promising alternative for shale gas fracturing instead of water. However, most studies pay more attention to the fracture generation and ignore the flow characteristic of SC-CO2 jet fracturing in limited perforation scenarios. To accurately explore the flow field in a limited perforation tunnel, a numerical model of a SC-CO2 jet in a limited perforation tunnel before fracture initiation is established based on the corresponding engineering background. The comparison between the numerical simulation and experiments has proved that the model is viable for this type of analysis. By using the numerical method, the flow field of the SC-CO2 jet fracturing is analyzed, and influencing factors are discussed later. The verification and validation show that the numerical model is both reliable and accurate. With the dramatic fluctuating of turbulent mixing in a fully developed region, there is an apparent increase in the CO2 density and total pressure during limited perforation. When the z increases from 10 times r0 to 145 times r0, the velocity on the perforation wall surface would decrease below 0 m/s, resulting in backflow in the perforation tunnel. The structure of the nozzle, including the outlet length and outlet diameters, significantly affects the axial velocity and boosting pressure in the perforation tunnel. The highest total pressure exists when the nozzle length-to-radius ratio is 2. The maximum velocity of the jet core drops from 138.7 to 78 m/s, and the “hydraulic isolating ring” starts disappearing when the radius changes from 1 to 1.5 mm. It is necessary to increase the aperture ratio as much as possible to ensure pressurization but not over 1. Based on a similar theory high-speed photography results clearly show that the SC-CO2 develops to fully jetting in only 0.07 s and a strong mixing exists in the annular region between the jet core and the surroundings, according with the numerical simulation. This study should be helpful for scholars to comprehensively understand the interaction between the SC-CO2 jet and perforation, which is beneficial for studying SC-CO2 fracturing.

A novel algorithm to estimate the CO2 flows across the critical point with real gas effects

This paper describes a new algorithm to accurately estimate the thermodynamic and transport properties of carbon dioxide based on six thermodynamic models and experimental data. The lookup table algorithm based on the least square method establishes a significant level of accuracy in predicting real gas properties. An extensive evaluation of the current approach is presented by comparing the values of predicted properties with different types of equations of state such as cubic, virial and multiparameter; experimental data was employed as reference properties. This algorithm can be directly executed to calculate the thermodynamic properties of generic fluids at any thermodynamic region. Moreover, the accurately estimated properties hold a great promise in developing an efficient empirical equation of state.The real gas property look-up table method is incorporated in a computational flow solver and employed to simulate jet impingement of supercritical carbon dioxide. First, the heat transfer characteristics of subsonic supercritical carbon dioxide jet impingement on a flat plate is calculated at varying angle and temperature. Next, the distance and structure of the Mach disk resulting from the impingement of supersonic supercritical carbon dioxide jet on a flat plate are analyzed.

Transient wellbore temperature and pressure calculation model for supercritical CO2 jet fracturing

ABSTRACT Supercritical carbon dioxide (SC-CO2) jet fracturing is a new technology, and it has many significant advantages compared with hydraulic fracturing. Ensuring the CO2 at supercritical state at the jet point is the key to the effective implementation of this technology. Therefore, this research proposes a numerical model to predict the jet point CO2 temperature and pressure for SC-CO2 jet fracturing. In this model, the effect of the tubing, casing, and cement sheath on heat transfer are all taken into consideration; the heat transfer is considered to be transient. The numerical results show that under the condition of high tubing injection rate, increase injection temperature and annulus injection rate both are not effective ways to make sure the CO2 temperature at the jet point exceeds its critical value. Therefore, in order to keep the CO2 at the jet point remains in a supercritical state, the tubing injection rate needs to be optimized. The CO2 pressure at the jet point is always exceeded its critical value during the process of supercritical carbon dioxide jet fracturing.

Experimental study on shale fracturing enhancement by using multi-times pulse supercritical carbon dioxide (SC-CO2) jet

Supercritical Carbon Dioxide (SC-CO2) fracturing can increase shale gas production and reduce carbon dioxide (CO2) emission. In order to enhance shale fracturing, a new method of multi-times pulse SC-CO2 jet fracturing is proposed and comprehensively studied. The results demonstrate there are more initiation positions and more complex fracture network after pulse SC-CO2 jet fracturing due to strong impingement and pressurization. Furthermore, three types of main fracture and four types of fracture branch are observed. The main fractures mostly initiate from perforation and propagate with irregular path to the specimen edge. CO2 absorption and fracture volume increase 77.72% and 2283%, respectively, more than that of single-pulse SC-CO2 jet fracturing. The comparison indicates that SC-CO2 creates more complex fracture morphology, larger fracture volume and CO2 absorption than that of water. Moreover, the effect of influential factors, including pulse jet frequency, pulse jet pressure and pulse jet distance, are discussed thoroughly. Thus, this study provides a method of jet fracturing enhancement, and is instructive for understanding and tackling pulse jet fracturing issue related to CO2 utilization and fracturing of shale reservoir.

Numerical Investigation of Rock Breaking Mechanism With Supercritical Carbon Dioxide Jet by SPH-FEM Approach

As a novel technology in the field of petroleum exploitation, rock breaking with supercritical carbon dioxide (SC-CO2) has considerable social and economic benefits. To investigate the rock breaking mechanism under SC-CO2 jet impacting in terms of mass and energy conservation, a fluid-solid coupling numerical model was established using smoothed particle hydrodynamics (SPH) method coupled with the finite element method (FEM). Jet movement feature and the stress distribution rule of impact target were obtained. Moreover, the space-time evolution of erosion cavity and failure process of elements were analyzed. The numerical research results are as follows: (1) the hybrid algorithm of SPH-FEM was effective for obtaining the numerical representation of rock breaking process under SC-CO2 jet impacting, and the simulation results were in good agreement with the experimental data. (2) The asymmetrical distribution characteristics of monitored points caused the erosion cavity to deviate from the geometrical center of the target face. (3) Soft rock under SC-CO2 jet impacting presented two failure forms: erosion and exfoliation. (4) The process of rock breaking with SC-CO2 jet was as follows: when the jet came into contact with the target plane, the pressure stress on the mating face and shear stress on the contact edge dominated the evolution of initial compression-shear failure zone. Thereafter, the high diffusivity-driven SC-CO2 penetrated into tiny cracks or pores near the failure zone, and strong air wedge effect caused tensile failure. With continuous high-speed impacting, the initial failure zone extended to a larger primary failure zone. Moreover, a few discrete failure zones were formed due to the high uncertainties of particles' motion trajectories, which mutually contributed to the main failure zone, and the erosion cavity was formed. When the jet became steady, quasi-static action was applied to the rock sample, and the erosion range expanded continuously.

Analysis of the flow characteristics of the high-pressure supercritical carbon dioxide jet

The supercritical carbon dioxide (SC-CO2) jet has a wide application prospect for rock breaking and jet fracturing in the development of the unconventional shale energy, due to its special physicochemical properties. To investigate its jet flow characteristics, the high-speed photography is used in experiments and the simulations through a compressible numerical model are carried out. It is shown that the jet flow field can be divided into three typical regions, the mixing layer possesses the same characteristics as a gas/gas turbulent mixing layer, with the divergent angles evidently smaller than those of the incompressible jets. The predicted results by the numerical model are in a good agreement with those of the experimentations. Through the dimensionless analysis, the potential core shows a length of about 9d and an increasing trend with the increase of the inlet pressure while the decay rate shows a decreasing trend, and the radial profiles consistent well with the “Ue - η” normalized method. In addition, a significant temperature drop of the SC-CO2 is observed between the nozzle inlet and the exit. A simple and convenient semi-empirical equation for calculating this temperature variation is deduced. Finally, the flow characteristics suggest that the SC-CO2 jet should be treated as a compressible jet.

Wellbore temperature and pressure calculation model for supercritical carbon dioxide jet fracturing

ABSTRACTA new numerical calculation model for wellbore temperature and pressure for SC-CO2 jet fracturing was proposed in this research. In our model, the impact of tubing, casing, and cement on heat transfer, and the heat generated by fluid friction losses are all taken into consideration. The CO2 physical properties are calculated by the Span–Wagner and Vesovic models. Based on our calculation model, the factors that may affect the wellbore temperature and pressure are discussed. The results indicated that ignoring the influence of the cement sheath thermal resistance on heat transfer would lead to a wellbore temperature higher than the actual value. The wellbore CO2 pressure is always higher than its critical value, but the CO2 temperature at the jet point in some cases is lower than its critical value. The wellbore CO2 temperature is increased with the increase in injection temperature and cement sheath thermal conductivity and the decrease in annulus injection rate and coiled tubing injection rate. However, the decrease in the coiled tubing injection rate and increase in the cement sheath thermal conductivity are the only effective ways to ensure that the CO2 temperature at the jet point exceeds its critical value.