Wellbore Temperature Research Articles

Study on wellbore temperature of riserless mud recovery system by CFD approach and numerical calculation

Abstract The riserless mud recovery (RMR) system abandons the riser used in conventional offshore drilling, and the drill string above the seabed is directly exposed to seawater, resulting in convective heat transfer from the drilling fluid in the drill string to seawater. Therefore, the wellbore temperature distribution in the RMR system is quite different from the conventional offshore drilling. In this paper, based on the heat transfer characteristics of the RMR system, a mathematical model of the thermal field of the RMR system is established. The data used in this paper come from a vertical well in the South China Sea. Computational Fluid Dynamics (CFD) software is used to simulate the temperature distribution in drill string at different seawater depths and different formation depths in this paper, and the simulation results are compared with the calculation results of the mathematical model, so as to verify the feasibility of the mathematical model established in this paper. Combined with the calculation results of the mathematical model, this paper also explores the effect of different discharge capacity and different injection temperature of drilling fluid on the wellbore temperature change.

Research on gas bubble formation using CFD during gas kick

Gas bubble formation behavior in the wellbore has influence on wellbore temperature and pressure by varying bubble movement characteristics. For now, most researches on gas bubble migration along the wellbore bases on bubble bed gas-liquid two-phase flow models in chemical industry, which is far away from the reality of the situation of wellbore during drilling process. Bubble channel is perpendicular to gravity and buoyancy during drilling, but it is parallel to gravity and buoyancy in the chemical industry. Based on computational fluid mechanics, gas bubble formation which channel perpendicular to buoyancy and gravity is simulated using CFD, the process of gas inflow, gas bubble formation and departure is analyzed. The flow field changes around bubbles and influential factors of gas bubble formation are also studied in this paper. Simulations indicate that the shape of the bubble during gas kick has always maintained asymmetric over development process. Formation pore radius and fluid density have significant effect on departure radius and time of gas bubbles, while the influence of fluid viscosity is slight. The main contribution here is that gas bubbles formation characteristics in bottom hole are revealed based on bubbles accumulation rules of bottom hole.

Geothermal exploitation by circulating supercritical CO2 in a closed horizontal wellbore

A novel method for geothermal development via supercritical CO2 circulation through a closed horizontal wellbore is proposed. Furthermore, a comprehensive transient model is built to analyze the wellbore temperature distribution for the new method, which considers the complicated heat transfer mechanisms in the coupled wellbore/formation system and the dynamic variations of CO2 flow behavior accompanied by the heat source/sink effect. The model is validated by experimental and model results quoted in the literature. The simulated results show that the outlet temperature decreases gradually with time and ultimately approaches a constant value. Affected by the significant variations in CO2 thermophysical properties, (1) a large buoyant drive will be provided by the density difference between the CO2 in the tubing and the CO2 in the annulus, (2) the simulation error for bottomhole temperature can reach 5.23 °C if the effect of flow work is neglected, and (3) the outlet temperature of CO2 is significantly larger than that of water at the same injection displacement. Moreover, the outlet temperature and heat mining rate can be greatly increased by adjusting the circulation direction of working fluids, and increasing the thermal insulation of the tubing and the length of the horizontal section.

Non-equilibrium multiphase wellbore flow characteristics in solid fluidization exploitation of marine gas hydrate reservoirs

In the core process of fractured marine gas hydrate (hereinafter referred to as hydrate) particles being transported up to the surface platform by airtight pipeline in the solid fluidization exploitation of marine gas hydrate reservoirs, influenced by the rising temperature and the dropping pressure, the solid hydrates will decompose and produce a large amount of gas at a certain critical point, causing the liquid–solid two-phase flow in the wellbore to change into complicated gas–liquid–solid multiphase non-equilibrium flow, which further aggravate well control, solid phase transportation and other safety risks. In view of this, the dynamic hydrate decomposition law in the above process was studied in this paper by establishing multiphase wellbore flow mathematical models of wellbore temperature and pressure field, hydrate phase equilibrium, hydrate dynamic decomposition in multiphase riser pipe flow, wellbore multiphase flow coupled hydrate dynamic decomposition, and a numerical calculation method was proposed and verified. The following results were obtained. First, by numerical model analysis, the effects of liquid phase displacement, solid throughput (daily gas production rate) and wellhead back pressure under different construction parameters on multi-phase non-equilibrium pipe flow were obtained. In addition, the field construction guidance measures were put forward based on multiphase non-equilibrium pipe flow characteristics as follows: to properly increase the solid throughput so as to increase the natural gas production, to appropriately increase the liquid-phase displacement and the wellhead back pressure so as to ensure well control safety. This study provides not only a theoretical basis for the prediction of multiphase non-equilibrium pipe flow in the solid fluidization exploitation, but a technical support for the field construction parameter optimization and well control safety.

A Coupled Transient Wellbore/Reservoir-Temperature Analytical Model

Summary This work presents a new coupled transient wellbore/reservoir thermal analytical model, consisting of a combined reservoir/casing/tubing system. The analytical model considers flow of a slightly compressible, single–phase fluid in a homogeneous infinite–acting reservoir system and provides temperature–transient data for drawdown and buildup tests at any gauge location along the wellbore. The model accounts for Joule–Thomson (J–T), adiabatic–fluid–expansion, conduction, and convection effects. The wellbore–fluid mass density is modeled as a function of temperature, and the analytical solution makes use of the Laplace transformation to solve the transient heat–flow differential equation, accounting for a transient wellbore–temperature gradient ∂T/∂z. The solutions presented assume moderate– to high–permeability reservoirs and do not consider skin effects in the formation. Results of the analytical model are compared with those of a commercial thermal simulator and with those of available models in the literature. Our model provides more accurate transient–temperature–flow profiles along the wellbore in comparison with previous analytical models in the literature. Furthermore, a generalization of a well–known parameter–estimation method from transient–temperature data is provided.

Study on the Wellbore Flow for Carbon Dioxide Fracturing

CO2 fracturing has unparalleled advantages in the reservoir reform which can significantly improve oil and gas recovery in unconventional oil and gas resources. The wellbore flow behavior is one of the fundamental issues of CO2 fracturing. A model of flow and heat transfer in the wellbore is developed in this paper, and wellbore temperature and pressure are coupled using an iterative method. The model is validated by measured data from the field. Wellbore pressure, temperature, CO2 properties, and phase state along depth are observed and a sensitivity study is conducted to analyze the controlling factors for CO2 fracturing. Results show that displacement is the key factor affecting CO2 flow behavior in the wellbore and injection temperature has greater influence on CO2 flow behavior than injection pressure and geothermal gradient; however, excess injection temperature brings enormous cost in wellbore pressure. CO2 phase state is related to working parameters and it tends to stay in liquid state under higher displacement, which is matched with field tests. This study can help optimize the working parameters of CO2 fracturing.

Calculation of the wellbore temperature and pressure distribution during supercritical CO2 fracturing flowback process

Supercritical CO2 fracturing is a new type of waterless technology developed in recent years. When the supercritical CO2 flows back after fracturing, the formation water is lifted by the upward movement of CO2. Since the pressure gradually decreases along the wellbore and the temperature also decreases due to the CO2 expansion, it is easy to result in the formation of hydrate under the conditions of high pressure and low temperature. In order to prevent the clogging of the wellbore due to CO2 hydrate, the wellbore temperature and pressure need to be predicted and regulated. Based on the Span-Wagner CO2 gas state equation and the Fenghour gas transport equation, combined with the classical wellbore flow heat transfer model, a supercritical CO2 fracturing flowback wellbore flow model with heat source and sink considered is developed, the dual coupling solution of axial and radial borehole is realized by iterating the pressure and temperature and coupling of tubing-annulus-formation. The results show that the wellbore pressure and temperature both decrease from the bottom to the top of the well, which is similar to the flow in oil and gas production. The parameters such as discharge output, tubing size, formation temperature gradient and pressure gradient have a great influence on the wellbore temperature and pressure. The reduction of the discharge output and the increase of the tubing size can effectively keep the wellbore temperature high and reduce the risk of CO2 hydrate formation. The discharge time has almost no effect on the wellbore pressure, and only slightly affects the wellbore temperature. The results can provide guidance for the study of supercritical CO2 fracturing flowback.

Numerical investigation on wellbore temperature and pressure during carbon dioxide fracturing

In the present study, a transient 2D model considering the factors of CO2 thermal properties, viscous heating source, Joule-Thomson effect, axial and radial heat transfer is proposed to investigate the wellbore temperature and pressure. The temperature governing equations are solved numerically by using the method of Alternating Direction Implicit (ADI). Based on the law of conservation of energy, the viscous heating source is reasonably considered as the thermal energy converted by mechanical energy. The wellbore temperature and pressure are analyzed based on the investigation of the tubing and annulus injection well with the diameter of 50.3 mm and depth of 3600 m. The simulation results of our model are in good agreement with the field data. The analysis results show that the bottom hole temperature increases first and then decreases as injection time increases. Large injection rate results in low bottom hole pressure and negative axial pressure gradient. The critical depth increases as injection time increases. Compared with tubing injection, tubing and annulus injection decreases critical depth and increases the duration of wellbore unsteady flow and heat transfer process. The solid heat conduction in axial direction significantly affects the wellbore temperature and pressure distributions.

Effect of silica nanoparticle size on the mechanical strength and wellbore plugging performance of SPAM/chromium (III) acetate nanocomposite gels

Cross-linked polymer gels are a new type of temporary plugging agent and are mainly used to control the leakage of fluid during drilling, completion, and workover operations. Improving the mechanical strength and plugging performance of these materials enables them to resist tough wellbore conditions (e.g., high pressure and high temperature). In this study, various concentrations and size of silica nanoparticles are introduced into the sulfonated polyacrylamide (SPAM)/chromium (III) acetate system to produce a nanocomposite with enhanced mechanical properties. First, the rheological behavior of gelant and viscoelastic properties of synthesized nanocomposites are investigated. Then, the surface chemistry and morphology of the synthesized gels is evaluated by Fourier transform infrared (FTIR) spectroscopy and field emission scanning electron microscopy (FESEM), respectively. Finally, the maximum sealing differential pressure for gels for temporary plugging of a wellbore is measured by applying differential pressure across the nanocomposite gel in a designed set-up. The results showed that the precrosslinking reaction and the gelant viscosity are directly related to the size and concentration of the silica nanoparticles as well as the wellbore temperature. Moreover, it is demonstrated that nanocomposites containing 20–30 nm sized particles have a higher mechanical strength and plugging capability in comparison to composites containing silica particles with sizes of 7–10 and 60–70 nm. The effect of silica nanoparticle size and concentration on the mechanical strength and wellbore plugging performance of SPAM/ chromium (III) acetate nanocomposite gels was investigated. First, the rheological behavior of gelant, surface chemistry, morphology, and viscoelastic properties of synthesized nanocomposites were investigated. In addition, an experimental setup was designed to determine the maximum differential compressive pressure (DCP) that the synthesized nanocomposite gels can tolerate before failing. The nanocomposites containing 20–30 nm particles have a higher DCP in comparison to those having 7–10 and 60–70 nm nanoparticles.

Exploring alteration of near-wellbore geothermal gradient during fluid circulation and production

Abstract The constant undisturbed formation temperature profile controlling heat transfer into the wellbore appears counterintuitive in light of transient cooling of the formation that occurs upon fluid circulation in drilling and also heating during fluid production. This study presents a mathematical model that shows that the heat transfer occurs from the wellbore/formation interface, not from some distance away from the wellbore wherein the initial formation temperature profile remains undisturbed. This new model allows investigation of heat transfer behavior from the formation into the wellbore during drilling or fluid circulation, and from the wellbore into the reservoir in the production mode. Application of the line-source solution for the temperature diffusivity equation for a steady-state system provides the necessary ingredients for computing the temperature behaviors at different times and radii. This line-source solution can be used throughout the wellbore to determine the undisturbed formation temperature, which may be used to obtain the geothermal gradient dependent on the radius and fluid circulation time. Therefore, the initial geothermal gradient works as a time-dependent variable, and the resultant second-order polynomial relationships can describe the undisturbed formation temperature. This study provides the required tools to assess the wellbore heat-transfer behavior and their effect on the wellbore temperature profiles. Also, the new mathematical model illuminates the impact of heat transfer by comparing its performance with the original formulations. Besides, this paper presents a complete derivation of the line-source solution of the temperature diffusivity equation to justify the proposed approach.

Establishing a practical method to accurately determine and manage wellbore thermal behavior in high-temperature drilling

As deeper reservoirs are pursued around the globe, the oil and gas industry has shown a keen interest in high-temperature operations, despite the significant drilling problems such operations pose. In order to formulate guidelines to manage wellbore temperatures accurately and maintain drilling safety, it is crucial to develop a method to quantitatively identify the effects of various parameters, both controllable and uncontrollable, on circulating fluid temperature through sound statistical methods with field validations. In this paper, the transient heat transfer mechanisms of each region of wellbore and formation were investigated. Based on the first law of thermodynamics, a set of transient heat transfer models were developed and solved using the fully implicit finite difference method. The change in the thermal behavior of the wellbore and formation was analyzed to ascertain the range of change in the sensitivity parameters. Using the Monte Carlo simulation technique, the input parameters were treated as uniform, and triangular distributions were applied to estimate the probability distribution of the bottom-hole temperature. The contributing factors of the bottom-hole temperature were ranked based on their level of influences as fluid heat capacity, formation thermal conductivity, inlet temperature, flow rate, and fluid density. The research findings from this study provides a quantitative evaluation of each parameter’s relative significance to circulating fluids temperatures during oil and gas wells or geothermal well drilling operations and therefore provides practical guidance in managing downhole temperatures by identifying the most effective and controllable operation parameters.

Theoretical Analysis and Numerical Simulation of Multi-Fields Coupled Variation During Deepwater Hydrate-Bearing Reservoir Exploitation

Natural gas hydrate is regarded as a kind of potential alternative energy resource and attracts the attention all over the world. Geological surveys have found that most natural gas hydrates are buried at the bottom of the sea. Several development methods, such as depressurization, thermal stimulation and inhibitor injection are proposed gradually on the basis of hydrate special properties, obtaining certain trial-produce performance. It is of great significance to learn the flow rules underground for production safety guarantee and efficiency improvement. However, the special phase transition of hydrate between solid and fluid accompanied by energy and mass change makes it difficult to predict and describe the parameters variations during hydrate-bearing exploitation. Since the hydrate is always sensitive to surrounding conditions, the disturbance of ambient pressure and temperature can change the corresponding phase equilibrium temperature, pressure and even phase transition rate. On the one hand, hydrate dissociation/reformation is an endothermic/exothermic reaction and releases/consumes large amount of gas in the limited space, reacting on the ambient pressure and temperature. On the other hand, hydrate phase transition also induces particles (hydrate, ice, sand, etc.) separation, aggregation and migration, altering the original hydrate saturation, reservoir properties (thermal conductance, permeability, skeleton structure, bonding strength, etc.) and multiphase flow. Then the heat and mass transfer in porous medium driven by the pressure difference and temperature difference influences the ambient conditions. Therefore, it is a complex coupled process with a series of variables. In this research, interaction mechanism between hydrate phase transition and porous media properties has been analyzed through influencing factors and the coupled relationship between multi-fields (containing temperature field, pressure field and seepage field) has been obtained. Taking the deepwater characters into consideration, the wellbore temperature and pressure distribution has been predicted by numerical simulation firstly as the boundary conditions of neighborhood hydrate-bearing reservoir. After proposing assumptions for simplification, the multi-flow model in hydrate- bearing reservoir has been built. Then applying production data referred from existed literatures and field reports, the multi-fields coupled variations during exploitation of hydrate-bearing reservoir have been simulated by the multi-flow model. The results indicated that although the temperature gradient of sea water reduce the wellbore temperature and the pressure gradient increase the wellbore pressure gradually, the ambient conditions are still disturbed significantly and become closer to hydrate phase transition requirements (10~30 MPa, 10~60℃). The near- wellbore temperature increases and pressure decreases earliest, and the variation area spreads towards the further reservoir. As time goes on, the disturbed zone becomes larger and larger but spread rate becomes lower and lower. Combining the reservoir temperature and pressure distributions with the hydrate phase equilibrium, corresponding hydrate phase transition can be analyzed and natural gas production can be estimated, providing a certain theory support for deepwater hydrate-bearing reservoir multi-fields prediction and efficient production.

Establishment of Wellbore Temperature Field During High Temperature and High Pressure Well Cementing in Western South China Sea

The western part of south China sea is characterized by high geothermal gradient, abnormal overpressure development and narrow formation pressure window in the deep part of the basin. In the process of cementing, the annulus has high pressure consumption, high risk of leakage, and significant influence of temperature on the rheology and hydration of cement slurry. In order to accurately determine the rheological and rheological parameters of cement slurry and prevent possible well leakage, overflow and even blowout accidents in the process of cementing, it is necessary to establish a wellbore temperature field model in the process of cementing. Based on the data of the actual drilling well, the variation of wellbore temperature under different pump displacement and circulation time is analyzed. The results show that the annular temperature is larger than the annular temperature at the beginning, and the annular temperature is larger than the annular temperature with the increase of depth. With the increase of displacement, the bottom hole temperature decreases and the outlet temperature increases. With the extension of the cycle time, the bottom hole temperature decreases and the outlet temperature increases. When the cycle time reaches a certain value, the bottom hole and outlet temperature remain basically unchanged.

Influence of the Riser Boost Line on the Thermal Stress of Riser in Deepwater Drilling

In deep water drilling, the existence of boost line makes the wellbore temperature change violently, and the thermal stress caused by it has a great influence on the strength of the riser. The paper considers the variable mass flow caused by the boost line fluid entering the wellbore during deepwater drilling. Based on the principle of conservation of mass and energy, the paper establishes a mathematical model for transient heat transfer in different regions of the wellbore and formation, analyzes the effect of the displacement of boost line on the temperature field of the wellbore, and calculates the transient stress of the casing under thermal effect. The results show that with the increase of cycle time, the temperature of the inner wall of the riser above the critical well depth first decreases and then increases. The thermal stress of the inner wall of the riser first increases and then decreases to zero, and then gradually increases, and the final thermal stress remains unchanged. With the increase of cycle time, the thermal stress of the inner wall of the riser increases with the increase of the circulating temperature of the inner wall of the riser below the critical well depth, and the rate of increase decreases gradually, and the final thermal stress remains unchanged. As the displacement of the riser increases, the circulating temperature of the inner wall of the riser increases, and the thermal stress on the inner wall of the riser increases. The research results can provide reference for the analysis of the factors affecting the riser stress in deep water drilling.

A New Prediction Method for Flashing Parameters in Heavy Oil Production by Steam Flooding

Flashing is a new problem in heavy oil production technology with steam flooding. It can cause pump air locks, pump and pump tubing damage, reduced production, and other problems. A difficulty in predicting flashing parameters involves accurate calculation of the bottomhole temperature and pressure. Based on the principles of heat transfer and fluid dynamics, we have proposed the following models: a model for the wellbore temperature distribution, a model for the stress distribution, a model for calculating the partial loss of pressure when the fluid flows through a fixed valve, and also a model for calculating the parameters for steam flooding of heavy oil, taking into account corrections for the influence of the parameters of the oil — water mixture on the steam critical temperature vs. pressure curve. Taking into account the nature of the fluid, the moisture content, the temperature and other wellbore parameters, the model permits real-time monitoring of flashing in the pump. Experiments were conducted on Jin 45-22-K281 wells. We performed a comparative analysis of the calculated and experimentally measured values. We have shown that the model for calculating flashing parameters is sufficiently accurate for the bottomhole fluid conditions. Analysis of the factors influencing the flashing effect may be useful for providing a theoretical basis for steam flooding parameters.

Corrosion Strength Analysis of Casing in Offshore Thermal Recovery Wells

Corrosion is a common problem in offshore oil and gas wells, especially in thermal recovery wells, which will greatly affect the residual strength of casing strings. Field data show that the corrosion pattern of casing is mainly pitting, local corrosion and uniform corrosion, of which pitting is the most common. For this reason, based on the engineering practice of thermal recovery well casing corrosion, the dynamic changes of wellbore temperature and pressure during the gas production process of thermal recovery wells are considered, and the numerical model of casing corrosion under transient temperature and pressure coupling is established. The influence of corrosion morphology and corrosion depth on the residual strength of the casing is analyzed. The transient stress variation law of the corroded casing is studied. The results show that: (1) Under the same corrosion depth, both pitting and uniform corrosion will reduce the residual internal pressure and external extrusion strength of the casing string, and the degree of influence is similar. The effect of uniform corrosion on the residual tensile strength of the casing string is larger than pitting and local corrosion; (2) the residual strength of the casing decreases linearly with the increase of the corrosion depth of the casing; (3) the stress of the corrosion part of the casing shows a significant dynamic change, in the initial stage of steam injection, casing stress rises rapidly at the corrosion position, and then the rate at which the casing stress rises is slowed, which tends to cause fatigue damage to the casing. The research results have reference significance for the assessment of the service status of offshore thermal recovery well casings.

A Heat Transfer Model for Accurate Wellbore Temperature Prediction during Drilling

A Heat Transfer Model for Accurate Wellbore Temperature Prediction during Drilling

Gas kick simulation in oil-based drilling fluids with the gas solubility effect during high-temperature and high-pressure well drilling

The high solubility of the invaded gas in oil-based drilling fluids and the heat transfer between annulus fluids and the surrounding formation make the accurate prediction and effective control of the bottomhole pressure (BHP) difficult during deep well drilling. In this study, a transient gas-liquid two-phase flow model considering the gas solubility and heat transfer effects is developed to simulate multiphase flow behaviors after gas kick in oil-based drilling fluids. Finite difference method is adopted to solve the governing equations. Predicted wellbore temperature and pressure distributions are in good agreement with field data, which indicates the accuracy of this model. Based on the proposed model, the flowing and thermal behaviors of gas and liquid phases in the annulus are compared when the gas solubility effect and the heat transfer effect are incorporated and not incorporated into the model. In the case of this study, without considering the gas solubility effect, the bottomhole pressure could be underestimated by 4.2% (2.92 MPa), while the bottomhole temperature is overestimated by 3.2% (3.74 °C). Without considering the heat transfer effect, the bottomhole pressure could be overestimated by 11.4% (7.94 MPa) under steady flow conditions. Besides, the effects of the reservoir pressure difference, choke pressure, geothermal gradient, and well depth on the wellbore pressure and temperature distributions are investigated. The results of this study may help field operators to accurately predict and effectively control the bottomhole pressure after gas kick in oil-based drilling fluids during deep well drilling.

Influences of Fracturing Fluid Injection on Mechanical Integrity of Cement Sheath under Four Failure Modes

The significant decreased wellbore temperature and increased casing pressure during fracturing fluid injection present a big challenge for the mechanical integrity of cement sheath in fracturing wells. Based on the theories of elastic mechanics, thermodynamics, and a multi-layer composed thick-wall cylinder, this paper proposed a new mechanical model of cement sheath for fracturing wells, coupling pressure, and thermal loads, which consider the failure modes of de-bonding, radial cracking, disking, and shear failure. The radial nonuniform temperature change and the continuous radial stress and radial displacement at two interfaces have been considered. With the proposed model, the radial distributions of failure stress and the corresponding safety factor for cement sheath during fracturing fluid injection have been analyzed and compared under four failure modes. Results show that the decreased wellbore temperature will produce significant tri-axial tensile stress and induce cement failure of de-bonding, radial cracking, and disking. The increased casing pressure will significantly lower the risk of de-bonding but also aggravate radial cracking and shear failure. For integrity protection of cement sheath, increasing the injected fluid temperature, maintaining higher circulation pumping pressures, and adopting cement sheath with a low elasticity modulus have been suggested for fracturing wells.

Transient temperature prediction models of wellbore and formation in well-kick condition during circulation stage

In the exploration and development of deep reservoir resources, well kick often occurs during drilling. The occurrence of well kick can change the flowing state and the various properties of the drilling fluid, which can have a very important impact on the wellbore temperature distribution. Based on the actual situation in the drilling process, the wellbore and formation heat transfer model in the case of normal circulation and in the case of well kick in the open-hole formation was established. The model was discretized by using the finite volume method and solved with under-relaxation iterative method. By comparing with previous research results, the validity of the model was established. Compared with the condition of normal circulation, the occurrence of well kick significantly changes the wellbore temperature distribution and has an important influence on the temperature difference profile and formation radial temperature distribution. Sensitivity factors that affected the wellbore temperature distribution were analyzed. Based on the difference in wellbore temperature distribution under normal circulation conditions and well kick conditions, this paper proposes a new method to detect the occurrence of well kick by monitoring the annulus temperature change. The new method can provide guidance for the well control operations and drilling operations.