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The gas kick represents a major risk in deepwater oil and gas exploration. Understanding the dynamics of gas kick evolution and the associated pressure response characteristics is critical for effective well control. In this paper, we introduce a transient wellbore multiphase flow model specifically developed to simulate gas kick in deepwater dual-gradient drilling, incorporating a downhole separator. The model accounts for the variable mass flow within the annulus and heat exchange between the annular fluid and the formation. Using this model, we analyzed the multiphase flow and thermodynamic behavior during the gas kick. Simulation results reveal a progressive increase in bottom-hole temperature, underscoring its potential as a key indicator for gas kick early detection. Additionally, variable gradient parameters affect not only the annular equivalent circulating density (ECD) profile but also the evolution of the gas kick. The inclusion of a downhole separator alters the annular ECD profile, creating a "broken line" shape, which enhances adaptability to the multi-pressure systems typically encountered in deepwater formation. By adjusting factors such as hollow sphere concentration, separator position, and separation efficiency, the annular ECD profile can be effectively customized. This study provides important theoretical insights and practical applications for utilizing dual-gradient drilling technology to address challenges in deepwater formation drilling. [ABSTRACT FROM AUTHOR]

As oil and gas exploration gradually advances into deep waters, the combined effects of various types of gas kick and the accurate calculation of the gas-kick volume have gained increasing attention. This study focused on gas kicks from permeable gas-bearing formations, considering the mass transfer of gas in the filtration region of the drilling fluids and revealed the mechanisms of seepage-driven and diffusion-driven gas kicks. Based on seepage mechanics and diffusion theory, a comprehensive model for calculating gas-kick volume was established, considering the synergistic effect of gas-concentration-diffusion and negative-differential-pressure, as well as mass transfer in both the filtrate zone and the filter-cake zone. The new model showed high calculation accuracy. The sensitivity analysis showed that both the seepage-driven and diffusion-driven gas-kick volumes in the wellbore increased with increasing formation porosity and open-hole length, while the thickness of the filter cake had a strong inhibitory effect on both. Additionally, a "seepage–diffusion ratio" was introduced to reveal the gas-kick evolution pattern under a seepage–diffusion mechanism. Under specific case conditions, when the seepage–diffusion ratio was less than approximately 1%, diffusion-driven gas kick contributed more than seepage-driven gas kick; when the seepage–diffusion ratio exceeded 1%, seepage-driven gas kick contributed more than diffusion-driven gas kick. The research can provide crucial parameters for wellbore multiphase flow calculation and wellbore pressure prediction. [ABSTRACT FROM AUTHOR]

The efficient exploitation of marine oil and gas resources holds significant potential to mitigate the current severe energy crisis. Regrettably, incidents, such as gas kick and even blowouts, can significantly impact normal development activities. The displacement kill method is one effective strategy for well control in deep-water areas. In this study, the detailed mathematical method for determining kill parameters involved in the kill operation by using the displacement kill method was proposed. Of course, this includes both cases: one where the kill fluid leaks during the kill process and another where no leakage occurs. Meanwhile, its applicability was verified through comparison with experimental results. Then, evolution characteristics of kill parameters, when killing fluid leakage occurs and when it does not occur, were analyzed. Finally, factors, such as pit gain and shut-in casing pressure, affecting the kill parameters of kill operation, were explored. It was found that the experimental and calculated results show great similarity, although there are slight differences between them. The total kill time in the simulation is 44 s shorter than that in the verification experiment. This indicates that the model established in this study is suitable for simulating the process of kill operation using the displacement kill method. In addition, the investigation results show that leakage of kill fluid increases the difficulty of the kill operation and prolongs the operation time. The number of kill cycles in the presence of kill fluid leakage is one more than that when there is no fluid leakage, resulting in an additional 70 min of total duration. Furthermore, the increase in pit gain and the rise in shut-in casing pressure can also pose challenges to the kill operations. The total kill time will be extended by 164 min when the mud pit gain increases from 20 m3 to 50 m3. The number of kill cycles rises by two when the shut-in casing pressure is increased from 5 MPa to 20 MPa. To ensure the safety of the drilling operation in abnormally high-pressure reservoirs, it is crucial to monitor parameters such as casing pressure during the drilling process and timely well control measures. [ABSTRACT FROM AUTHOR]

As a non-invasive tool, ultrasound waves can be applied to probe gaseous content of the drilling fluid in offshore oil-drilling operations. The approach is believed to improve sensitivity and accuracy of a gas-kick detection system. In this research, four types of bubble flow are designed to simulate undeveloped gas kicks, and their effects on changes of ultrasound waves are investigated. The bubbles are found to have changed power distribution of the sound waves that have been reflected by the bubbles and received by side sensors. The pattern of power spectrum changes around the master frequency is found to be closely related to the type of bubble flow. Such changes are grouped on the basis of cluster analysis, and it is found that bubble strings and bubble groups would produce substantially different effects and that bubble mergences would largely alter spectral property of the sound waves. By establishing relationship between power-change pattern of sound waves and the behavior of a bubble flow, the research is intended to seek a more predictive way of recognizing early-stage gas kicks for offshore oil-drilling practices. [ABSTRACT FROM AUTHOR]

Natural gas is easily soluble in oil-based muds (OBM), leading to complex flow behavior in wellbores, especially in horizontal wells. In this study, a new transient flow model considering wellbore-formation coupling and gas solubility on flow behavior is developed to simulate gas kicks during horizontal drilling with OBM. Furthermore, the effect of gas solubility on parameters such as bottom-hole pressure (BHP), gas void fraction and mixture velocity in the flow behavior is analyzed. Finally, several critical factors affecting flow behavior are investigated and compared to gas kicks in water-based muds (WBM) where the effect of solubility is neglected. The results show that the invading gas exists as dissolved gas in the OBM and as free gas in the WBM. Before the gas escapes from the OBM, the pit gain is zero and there is barely any change in the BHP, annulus return flow rate and mixture velocity, which means that detecting gas kicks through these warning signs can be challenging until they get very close to the surface and develop rapidly. However, in WBM drilling, these parameters change quickly with the increasing gas kick time. Additionally, for both cases, the longer the horizontal length and the greater reservoir permeability, the greater the decrease in BHP, and the shorter the time for gas to migrate from the bottom-hole to the wellhead. A larger flow rate contributes to a greater initial BHP and a lesser BHP reduction. This research is of value in characterizing gas kick behavior and identifying novel ways for early gas kick detection during horizontal drilling with OBM.

As oil and gas exploration gradually advances into deep waters, the combined effects of various types of gas kick and the accurate calculation of the gas-kick volume have gained increasing attention. This study focused on gas kicks from permeable gas-bearing formations, considering the mass transfer of gas in the filtration region of the drilling fluids and revealed the mechanisms of seepage-driven and diffusion-driven gas kicks. Based on seepage mechanics and diffusion theory, a comprehensive model for calculating gas-kick volume was established, considering the synergistic effect of gas-concentration-diffusion and negative-differential-pressure, as well as mass transfer in both the filtrate zone and the filter-cake zone. The new model showed high calculation accuracy. The sensitivity analysis showed that both the seepage-driven and diffusion-driven gas-kick volumes in the wellbore increased with increasing formation porosity and open-hole length, while the thickness of the filter cake had a strong inhibitory effect on both. Additionally, a “seepage–diffusion ratio” was introduced to reveal the gas-kick evolution pattern under a seepage–diffusion mechanism. Under specific case conditions, when the seepage–diffusion ratio was less than approximately 1%, diffusion-driven gas kick contributed more than seepage-driven gas kick; when the seepage–diffusion ratio exceeded 1%, seepage-driven gas kick contributed more than diffusion-driven gas kick. The research can provide crucial parameters for wellbore multiphase flow calculation and wellbore pressure prediction.

High pressures during drilling with the aim to obtain hydrocarbon formations (oil and natural gas) can cause an uncontrolled eruption. Therefore, it is necessary to look for warning signs of kicks and control the formation strength. The aim of this article is to show a real process of fracture pressures during a gas kick and their possible solutions. The evaluation of the lithological structure of formations and the correct evaluation of seismic measurements are closely related to the issue of fracture pressures. The contribution also includes software data for detailed analysis and calculations of formations pressures. We point out the incorrect calculation of the geological lithology and employ a casing shoe; it is a risky decision to use a formation integrity test as opposed to a leak of the test. Based on theoretical knowledge, we compared and verified the recalculation of pressure coefficients during the gas kick. In our case, we propose possible solutions for cracking a casing shoe. We point out the importance of correct calculations for a safe and economical purpose. In this post, a theoretical example was shown where the system of casings was correctly designed, and based on this, we obtained ideal values of the fracture pressures. In the end, we proposed an algorithm to simplify work procedures during well control to minimize formation pressures against the deposit and casing shoe. [ABSTRACT FROM AUTHOR]

Gas kick monitoring is of great significance for prevention of blow-out accidents, especially in deep drilling and deep-water drilling. In this study, a machine learning (ML) model for early-monitoring of gas kick is developed using the ensemble learning algorithms based on 7363 lines of drilling logging data at South China Sea. The selected input parameters based on mechanism analysis of gas kick are six fast engineering parameters, including hook load (WHO), weight on bit (WOB), torque (TOR), flow rate (FLW), rate of penetration (ROP) and stand-pipe pressure (SPP), and two slow mud property parameters, i.e. electrical conductivity (CON) and mud outlet density (DEN). The model is constructed using RUSboosted, Subspace-KNN and Bagged Trees algorithms, and is compared with the neural network algorithm. We propose a comprehensive error to quantitatively evaluate the performance of the gas kick monitoring models. The models for early-monitoring of gas kick are applied for a single well and multiple wells, respectively. The results indicate that: (i) The optimal combination of input parameters is made up of six fast engineering parameters and two slow mud parameters. When there is a higher requirement on timeliness, only use of the six fast engineering parameters is also acceptable. (ii) The ensemble learning models work well when the input data expand from single well to multiple wells in the same block. For most cases, the prediction error of the optimal model is below 10%. The RUSboosted algorithm performed best in most data sets. (iii) Gas kick identification from lots of drilling logging records is mathematically a small-sample problem. The output labelling of a potential gas kick should be based on the field practical requirement. The recommended positive length of continuous-point labelling method is 5 m for the studied area, which can effectively reduce the average error from 8.02% to 5.48%. [ABSTRACT FROM AUTHOR]

Deep wells control safety problems have always been the focus of attention due to the influence of complicated geological conditions, such as high-temperature and high-pressure (HTHP). Considering the mathematical model is only approximation of reality, thus the continuous transmission of real-time measurements is more popular, which can be used to identify the undetermined downhole parameters and improve accuracy of the model predictions. In the current study, we use two pressure while drilling tools to monitor downhole parameters in real time. Firstly, combined with the unscented-Kalman-filter (UKF) algorithm, a well hydraulics forward model with density factor and friction factor based managed-pressure-drilling (MPD) system is developed to quantitatively analyze the actual transient annular pressure. Secondly, a new multi-phase flow inversion model is established by determining the inversion parameters as gas kick rate and the position of the gas kick, which is used to track the values of pressure and outlet flow rate in real-time. The results of the case indicate that the inversion accuracy of the inversion parameters increases with the distance between dual-measurement points, and the reasonable value is selected as 30 m. Additionally, the proposed model is successfully validated using synthetic data and experimental data, where the maximum errors in predicting the position of the gas kick are only 3.1% and 5.3% when tuning the model stably tends towards the true value, respectively. The proposed model achieves accurate quantitative interpretation and analysis of downhole gas kick conditions, further clarifies the previously unknown key parameters of downhole gas kick, and has important significance for the realization of safe and efficient drilling. [ABSTRACT FROM AUTHOR]

Abstract Hydrate phase transition may bring hidden dangers for well control safety, even accidents of blowout happen in deep water drilling. Accurate calculation of all the drilling parameters is of great importance for well control safety. In this study, the mathematic models of transient heat transfer and multiphase flow have been established with the consideration of hydrate phase transition. Furthermore, the position where hydrate formation is most likely to occur was predicted with the proposed models, and the factors affecting hydrate formation region were also analyzed. Finally, the analysis of the effect of gas hydrate phase transition on some important parameters in well control, such as the pit gain, gas void fraction, and bottom hole pressure, is presented. The results show that hydrates form near the mud line during the drilling and shut‐in stage, but the hydrate formation region will be narrowed as well killing start. Additionally, the hydrate formation region decreased with the increase of flow rate and increased with the increasing shut‐in time, hydrate inhibitors, and riser insulation are presented to prevent hydrate blockage. More importantly, the gas void fraction and pit gain decrease due to the formation of hydrates, leading to the gas kick early detection not timely and gas kick more “hidden.”

Abstract Gas‐liquid displacement occurs often in fractured gas reservoirs, and can cause gas kick and mud leakage, resulting in a very high risk of losing well control. To analyze gas‐liquid displacement between borehole and gassy fracture, we used computational fluid dynamics to simulate its behaviors. We also used response surface methodology (RSM) to design numerical experiments. The effects of fracture width, bottom‐hole differential pressure, mud density, mud viscosity, and mud displacement were taken into account. We used RSM to determine the influence of the multifactor interaction of gas‐liquid displacement and established an empirical formula for the gas displacement rate. The results show that gas‐liquid displacement is proportional to fracture width, bottom‐hole differential pressure, mud density, and mud displacement; however, the displacement is inversely proportional to mud viscosity. The sensitivity sequence of the gas‐liquid displacement rate is fracture width > bottom‐hole differential pressure > mud viscosity > mud density > mud velocity. The impact of fracture width is clearly higher than that of the other factors, while the mud velocity has almost no impact. Our established empirical formula can be used to predict bottom‐hole gas kick and drilling mud leakage and to inversely predict the fracture width and formation gas pressure.

Whenever gas kick occurs, gas flows in mixture with the flowing drilling fluid or migrate upwardly when drilling fluid is suspended. When wellbore temperature and pressure are higher than the critical temperature and pressure of natural gas, natural gas is in a supercritical state. In the process of gas migration along the wellbore, gas volume will gradually increase due to the decrease of wellbore temperature and pressure. At the critical point, phase behavior changes and gas volume increases very rapidly, which can bring great harm to well control; what is worse, it may lead to well blow out. Therefore, it is of great significance to analyse the effects of phase change characteristics of the supercritical fluid on well control safety. Due to the huge advantages and strong adaptability of Lattice Boltzmann method (LBM) to solve gas-liquid two-phase flow problem with complicated and changeable phase interface, wellbore gas-liquid phase transition based on inter-particle interaction of LBM method is researched in this paper. Simulation results show that different initial densities of mixed fluid have significant influence on gas and liquid phase distribution after phase transition. Continuous gas is formed in phase change position of a wellbore when initial density of mixed fluid is less than the critical density. And gas change in phase behaviour migrates along the wellbore as bubbles when initial density of mixed fluid is greater. Research results not only improve the understanding of gas-liquid phase transition mechanism, but also can provide some valuable attempts to promote the application of LBM method in wellbore gasliquid two-phase flow. [ABSTRACT FROM AUTHOR]

During industrial offshore deep-water drilling process, gas kick event occurs frequently due to extremely narrow Mud Weight (MW) window (minimum 0.01sg) and negligible safety margins for the well control purposes. Further, traditional gas kick detection methods in such environments have significant time-lag and can often lead to severe well control issues, and occasionally to well blowouts or borehole abandonment. In this study, firstly, the raw field data is processed through data collection, data cleaning, feature scaling, outlier detection, data labeling and dataset splitting. Additionally, a novel data labeling criterion for gas kick risks is proposed where five kick risks (Indicated by different colors in this study) are defined based on three key indicators: differential flow out (DFO), kick gain volume (Vol), and kick duration time (Time). Kick risk status represents one of the following cases: Case 0 - No indicators are activated (Green), Case 1 - Multi-drilling parameters deviation or DFO is activated (Orange), Case 2 - DFO and Vol are simultaneously activated (Light Red), Case 3 - DFO and Time are simultaneously activated (Light Red), Case 4 - DFO, Vol and Time alarms are simultaneously activated (Dark Red). Then, a novel data mining method using Long Short-Term Memory (LSTM) Recurrent Neural Network (RNN) is presented for early detection of gas kick events by analyzing time series data from field drilling process. The network parameters such as number of hidden layers and number of neurons are initialized to build the LSTM network. The learned LSTM model is evaluated using the testing set, and the best LSTM model (six (6)-layers eighty (80)-nodes (6 L*80 N)) is optimally selected and deployed. The accuracy of deployed LSTM model is 87 % in the testing dataset, which is reliable enough to identify the kick fault during the deep-water drilling field operation. Lastly, the LSTM model detected the gas kick events earlier than the "Tank Volume" detection method in several representative case studies to conclude that the application of LSTM model can potentially improve well control safety in the deep-water wells with narrow MW windows. [ABSTRACT FROM AUTHOR]

Hydrate phase transition may bring hidden dangers for well control safety, even accidents of blowout happen in deep water drilling. Accurate calculation of all the drilling parameters is of great importance for well control safety. In this study, the mathematic models of transient heat transfer and multiphase flow have been established with the consideration of hydrate phase transition. Furthermore, the position where hydrate formation is most likely to occur was predicted with the proposed models, and the factors affecting hydrate formation region were also analyzed. Finally, the analysis of the effect of gas hydrate phase transition on some important parameters in well control, such as the pit gain, gas void fraction, and bottom hole pressure, is presented. The results show that hydrates form near the mud line during the drilling and shut‐in stage, but the hydrate formation region will be narrowed as well killing start. Additionally, the hydrate formation region decreased with the increase of flow rate and increased with the increasing shut‐in time, hydrate inhibitors, and riser insulation are presented to prevent hydrate blockage. More importantly, the gas void fraction and pit gain decrease due to the formation of hydrates, leading to the gas kick early detection not timely and gas kick more "hidden." [ABSTRACT FROM AUTHOR]

Gas kick is a common and high-risk drilling trouble in geo-energy engineering, especially for deep-water drilling and ultra-deep well drilling. The most favorable way of early detection of gas kick is to move the detection from the wellhead or near surface to the downhole. In this paper, a new conception of downhole detection of gas kick using low-frequency elastic wave was put forward. The framework of coupling the multiple physic processes of gas-liquid two-phase annulus flow, bubble migration and low-frequency elastic wave propagation during gas kick was developed. The characteristic responses of low frequency elastic wave to gas kick were quantitatively analyzed based on multiphysics modeling under the ideal case and different levels of background gas (BGG), respectively. The modeling results indicated that: (i) The velocity decreases cliff-like and the attenuation coefficient increases significantly at the gas-kick bubble front. The change magnitudes of the velocity and the attenuation coefficient increase with the gas intrusion rate, and decrease with the pump displacement. The change magnitude of attenuation coefficient decreases with mud density, while the increase of velocity is not sensitive to the mud density. (ii) For the ideal case of the vertical well, the effective detection within the depth section of (2014–2568) meter could identify gas kick about (14.3–29.2) minutes earlier than the conventional pit-gain method. The gas kick could be identified earlier when the deviation angle is smaller and/or the monitoring point goes deeper. (iii) The changing magnitudes and rates of the velocity and the attenuation coefficient decrease with the BGG. The downhole detection of gas kick using low-frequency elastic wave should be reliable when the BGG is lower than 5%. The effects of rock cuttings, phase transition of the gas, and drill-string vibrations should be further investigated in future study. • Downhole low-f elastic wave method can identify gas kick much earlier than pit-gain method. • Characteristic responses of low-f elastic wave to gas kick are analyzed by multiphysics coupling. • The low-f elastic wave method is reliable for gas kick detection when BGG is lower than 5%. [ABSTRACT FROM AUTHOR]

Gas‐liquid displacement occurs often in fractured gas reservoirs, and can cause gas kick and mud leakage, resulting in a very high risk of losing well control. To analyze gas‐liquid displacement between borehole and gassy fracture, we used computational fluid dynamics to simulate its behaviors. We also used response surface methodology (RSM) to design numerical experiments. The effects of fracture width, bottom‐hole differential pressure, mud density, mud viscosity, and mud displacement were taken into account. We used RSM to determine the influence of the multifactor interaction of gas‐liquid displacement and established an empirical formula for the gas displacement rate. The results show that gas‐liquid displacement is proportional to fracture width, bottom‐hole differential pressure, mud density, and mud displacement; however, the displacement is inversely proportional to mud viscosity. The sensitivity sequence of the gas‐liquid displacement rate is fracture width > bottom‐hole differential pressure > mud viscosity > mud density > mud velocity. The impact of fracture width is clearly higher than that of the other factors, while the mud velocity has almost no impact. Our established empirical formula can be used to predict bottom‐hole gas kick and drilling mud leakage and to inversely predict the fracture width and formation gas pressure. [ABSTRACT FROM AUTHOR]

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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. [ABSTRACT FROM AUTHOR]

Abstract A gas kick may occur when drilling with narrow pressure margin, which can lead to significant non-productive time. This paper proposes an early gas kick detection method applicable to water-based mud (WBM), which integrates a transient pressure and temperature coupling model into an unscented Kalman filter (UKF) algorithm. Three pressure factors and a flow rate factor are estimated with the UKF algorithm using updated measurement data in a detection estimator, and a generalized likelihood ratio test (GLRT) is employed to automatically detect changes in the pressure factors and flow rate factor for prediction of the gas kick. Simulated results show that the estimated pressures and outlet flow rate trace synthetic measurements very well with continuous inversion of the pressure factors and flow rate factor. All of the estimated pressure factors and flow rate factor fluctuate to a little extent around a base value under normal drilling condition, while the pressure factor in annulus and flow rate factor both deviate from the base value when the gas kick occurs. Performances of the proposed method, pit gain monitoring method and delta flow monitoring method are contrasted. The kick detection times are gradually reduced for all the methods with the increase of gas kick rate. Moreover, the proposed method herein shows a much better performance than the pit gain and delta flow monitoring methods, especially at small gas kick rate. Highlights • A new early gas kick detection method is proposed. • Pressure factors and flow rate factor are estimated by unscented Kalman filter. • Temperature effect is considered in the detection method. • Superior performance of the gas kick detection method has been proved. [ABSTRACT FROM AUTHOR]

Effective well control depends on the drilling teams’ knowledge of wellbore flow dynamics and their ability to predict and control influx. Unfortunately, detection of a gas influx in an offshore environment is particularly challenging, and there are no existing datasets that have been verified and validated for gas kick migration at full-scale annular conditions. This study bridges this gap and presents pioneering research in the application of fiber optic sensing for monitoring gas in riser. The proposed sensing paradigm was validated through well-scale experiments conducted at Petroleum Engineering Research & Technology Transfer lab (PERTT) facility at Louisiana State University (LSU), simulating an offshore marine riser environment with its larger than average annular space and mud circulation capability. The experimental setup instrumented with distributed fiber optic sensors and pressure/temperature gauges provides a physical model to study the dynamic gas migration in full-scale annular conditions. Current kick detection methods primarily utilize surface measurements and do not always reliably detect a gas influx. The proposed application of distributed fiber optic sensing overcomes this key limitation of conventional kick detection methods, by providing real-time distributed downhole data for accurate and reliable monitoring. The two-phase flow experiments conducted in this research provide critical insights for understanding the flow dynamics in offshore drilling riser conditions, and the results provide an indication of how quickly gas can migrate in a marine riser scenario, warranting further investigation for the sake of effective well control.

Timely forecasting of the kick risk after a well kick can reduce the waiting time after well shut-in and provide more time for well killing operations. At present, the multiphase flow model is used to simulate and forecast the pit gain and casing pressure. Due to the complexity of downhole conditions, calculation of the multiphase flow model is difficult. In this paper, the time series analysis method is used to excavate the information contained in the time-varying data of pit gain and casing pressure. A forecasting model based on a time series analysis method of pit gain and casing pressure is established to forecast the pit gain and casing pressure after a kick. To divide the kick risk level and achieve the forecasting of the kick risk before and after well shut-in, kick risk analysis plates based on pit gain and casing pressure are established. Three pit gain cases and one casing pressure case are studied, and a comparison between measured data and predicted data shows that the proposed method has high prediction accuracy and repeatability.

A new design of nonlinear model predictive controller (NMPC) is proposed for managed pressure drilling (MPD) system. The NMPC is based on output feedback control architecture and employs offset-free formulation proposed in [1] . NMPC uses active set method for computing control inputs. The controller implements an automatic switching from constant bottom hole pressure (CBHP) regulation to flow control mode in the event of a reservoir kick. In the flow control mode the controller automatically raises the bottom hole pressure setpoint, and thereby keeps the reservoir fluid flow to the surface within a tunable threshold. This is achieved by exploiting constraint handling capability of NMPC. In addition to kick mitigation the controller demonstrated good performance in containing the bottom hole pressure (BHP) during the pipe connection sequence. The controller also delivered satisfactory performance in the presence of measurement noise and uncertainty in the system. [ABSTRACT FROM AUTHOR]

The ability to perform accurate pore pressure and reservoir inflow estimation during a kick incident is necessary, particularly when drilling in formations with narrow pressure margins. Currently available techniques for pore pressure estimation and reservoir characterization either rely on empirical correlations requiring access to well logging data and other petrophysical information, or require downhole pressure sensing and advanced flow metering capabilities. This paper introduces a model-based estimation technique which uses surface measurements commonly available in a Managed Pressure Drilling (MPD) system, coupled with a simplified transient two-phase model. This model is capable of representing essential dynamics during a gas kick with reduced computational overhead, but without sacrificing significant modeling accuracy. First, the model is validated in a gas kick scenario against experimental data, showing good agreement between key measured parameters and the model predictions, and thereby justifying the model applicability to field operations. Next, data generated from a commercial simulator test case is used to evaluate the proposed estimation methodology. The estimated pore pressure and reservoir productivity are close to their respective values from the commercial simulator, and the flow out rate and surface back-pressure predicted by the simplified two-phase model yield very good match against the simulator results. [ABSTRACT FROM AUTHOR]

The hydrate phase transition presents new problems and challenges for the deepwater well control in the drilling processes. A simulation model is built for deepwater gas kicks with consideration of the hydrate phase transition. The model is based on the multiphase flow governing equations and the hydrate phase transition calculation equations. The influence of the hydrate phase transition on the gas kick hydraulics is investigated through numerical simulations. It is shown that the diameter of the gas bubbles can significantly influence the hydrate phase transition effect. The influence of the hydrate phase transition on the gas kick hydraulics increases with the decrease of the average gas bubble diameter. The hydrate phase transition adds a “hidden” nature for the well kick in deepwater and hinders the early detection of the gas kick. The influence of the hydrate phase transition on the gas kick hydraulics is also studied in the case when the hydrate inhibitor is added to the drilling fluid. [ABSTRACT FROM AUTHOR]

In this work we deal with the no-slip drift-flux model for gas-liquid flow dynamics. We focus on a situation where there is a free interface separating the gas-liquid mixture from a pure gas region which takes a positive pressure p*. This situation is highly relevant for gas-liquid flow in the context of wellbore operations. Previous works have assumed that there is vacuum, i.e., the pressure p* is zero. The positive pressure p* > 0 creates a boundary term that must be treated in a consistent manner throughout the analysis. We derive time-independent estimates and make some observations related to the role played by p*. The estimates allow us to discuss the long-time behavior of the two-phase flow system. In particular, it is shown that the stationary solution connecting the gas-liquid mixture to the pure gas region with the specified pressure p* in a continuous manner is asymptotically stable for sufficiently small initial perturbations. The analysis clearly shows how this perturbation directly depends on the size of the outer pressure p*. A higher pressure p* allows for larger initial perturbations from steady state. One ingredient in the analysis is the rate at which the liquid mass decays to zero at the free interface. Insight into mechanisms that control the decay rate of the liquid mass at the free interface is also of interest since such transition zones often are associated with instabilities in numerical discretizations of two-phase models. [ABSTRACT FROM AUTHOR]

Uncontrollable blowout is a great drilling accident. For gas kick during drilling, in order to prevent uncontrollble blowout, the gas-liquild two-phase flow model is established, considering the kick characteristics in well kick and well killing process, and it is solved with finite difference method, given initial values in different periods. The results indicated that a one-to-one correspondence was established between standpipe pressure and kick rate and height while drilling, and another one-to-one correspondence was also established between casing pressure and kick rate and height while well killing. Based on the findings above, the standpipe pressure method and casing pressure method were proposed to detect kick, and the related coefficient method was used to judge the kick rate and height during drilling and killing. Meanwhile, a computer system was developed to judge kick velocity and height automatically, which provided a theoretical basis for kick parameter judgement. [ABSTRACT FROM AUTHOR]

Gas kick occurs frequently during deep-water drilling operations caused by the lack of safe margin between pore pressure and leakage pressure. The existing research is limited to gas kick classification and cannot quantitatively evaluate the gas kick risk in the downhole very well. Thus, the objective of this work is to systematically use Long Short-Term Memory (LSTM) Recurrent Neural Network (RNN) models based on pilot-scale rig data for quantitative evaluation of gas kick risk. Furthermore, the quantitative evaluation is not surface but downhole. First, the gas kick simulation experiment is accomplished in the pilot-scale test well and produces the gas kick dataset, which is based on the multi-source data fusion through the surface monitoring technologies, riser monitoring technologies and downhole monitoring technologies. Second, the training features are selected and grouped as Sets1-5 to study the features' sensitivity. Third, the raw data is processed and prepared for the following machine learning framework. Fourth, there are five (5) LSTM models trained on Sets1-5. The results indicate that the models' Loss decrease with the increase of feature number, which has fully demonstrated the effectiveness of PWD, EKD, and Doppler parameters. Finally, there are four representative case studies (artificial gas kick) that are used to test the above five models. The compressed air injected rate (AR) prediction error and detection time-delay decrease with the increase of feature number. The LSTM model trained with the combination of surface-riser-downhole comprehensive detection technologies performs the best in reducing both the prediction error and detection time delay, which could be used to quantitatively evaluate the downhole gas kick risk in the more accurate, faster, more stable, more reliable, and cost-effective manner, and it is effective and worthy of promotion. • The autonomous experiment setup in the pilot-scale test well is carried out to simulate deep-water gas kicks. • There are five novel LSTM models that are developed and proposed for downhole quantitative evaluation of gas kicks. • The proposed LSTM models could quantitatively evaluate the downhole gas kicks in the more accurate and faster manner. • The deployed LSTM models are applied in four representative case studies to further evaluate their performance. [ABSTRACT FROM AUTHOR]

For reliable gas kick detection modeling and simulation, the PVT properties of the gas must be predicted accurately. The property correlations available in open literature are developed mostly for certain regions and conditions, which usually over-predict or under-predict when applied to different regions and conditions. To assess these correlations and to determine their applicability and accuracy, a comprehensive evaluation is performed for 63 empirical correlations of four gas properties; gas-oil ratio GOR, oil formation volume factor OFVF, gas viscosity, and gas density based on published laboratory measurements. The GOR and OFVF correlations were evaluated on a regional basis and three best-fit correlations are recommended for each selected region including the Middle East, Central & South America, North America, Africa, and Asia. A universal new correlation for the GOR is developed in this study that can be used for any region in the world with better accuracy and wider range than all available correlations. Furthermore, based on the evaluation results, the most accurate correlations for gas viscosity and density at high-temperature and high-pressure (HTHP) conditions are recommended. The density-based models of the gas viscosity show close results within a minimum average absolute relative error (AARE) of 3.50% to a maximum of 4.45%. Further assessment for the equations of state based on real compositions of the gas kick is recommended for future work. The present work provides a comprehensive and one-stop source database for property correlations and measured data related to gas kick detection. [Display omitted] • Comprehensive evaluation of most suitable PVT correlations based on measurements. • Regional-based evaluation GOR, OFVF correlations and best-fit recommendations. • Utilizing full global data range to develop more accurate universal GOR correlation. • Assessment of correlations for gas viscosity and density at HTHP conditions. • Comprehensive one-stop source database for property correlations and measured data. [ABSTRACT FROM AUTHOR]

In the process of penetrating the reservoir by underbalanced drilling, with the increase of the penetrated reservoir thickness, the volume of gas kicking into the wellbore increases, which causes the drastic change of wellhead void fraction, leading to the bottom-hole pressure out of control. The changing of void fractions in different well depths are calculated during underbalanced drilling, and the influence of different air intake flow and wellhead back pressure on wellbore void fractions is analyzed. In consideration of wellhead pressure adding value on bottom hole pressure, the computing method of wellhead pressure of constant air intake flow is obtained for penetrating the reservoir by underbalanced drilling. The results show that gas rapidly expands when it reaches the surface, and the wellhead back pressure have a enormous effect on the void fractions at wellhead while have a little influence on the void fraction under 500 meters. Keeping the air intake flow constant, with the increase of the penetrated reservoir thickness, the wellhead pressure increases. The smaller the air intake flow, the bigger the wellhead pressure needs to load. [ABSTRACT FROM AUTHOR]

This study proposes a transient gas-liquid-solid multiphase flow model for gas kick during MPD, considering the effect of dynamic wellhead back-pressure, temperature field, and velocity relation of different phases. Based on this model, the gas kick control strategies and outflow response characteristics during MPD are thoroughly investigated. The simulated results reveal that, with the upward migration and expansion of the invading gas, the hydrostatic pressure and frictional pressure in the annulus changes accordingly, resulting in a non-linear relationship between the wellbore back-pressure and the bottom-hole pressure. Moreover, the effects of an under-balance pressure at the bottom hole, the pressure balance relationship between the formation and the bottom hole, the kick detection level, the well depth on the wellhead back-pressure control and the response behaviors of the outlet flow rate are discussed. The results of this investigation can provide engineering guidance for MPD to address the issue of gas kick. • A transient gas–liquid–solid flow model for gas kick during MPD is developed. • Temperature field and velocity relation of different phases are both considered. • Gas kick control strategies and outflow response characteristics are investigated. • Sensitivity analysis is conducted to study the wellhead back-pressure control rules. [ABSTRACT FROM AUTHOR]

The addition mud density is a key part of drilling fluid design to avoid drilling accidents resulting from the pressure surge. However, the current standard of addition mud density is empirical and whether this empirical value can be applied to all wells, especially deep wells, deserves further study. In this paper, in order to quantitatively calculate the variation of downhole pressure during tripping, the transient wellbore surge pressure calculation model during tripping was established and verified by field data fist. Then, through the analysis of the surge pressure and its influencing factors during tripping, it was found that the current standard of addition pressure difference cannot be used as an empirical value for different sections of a well, while the addition mud density was more reasonable for the open hole safety in casing program design. However, the surge pressure was much smaller than the lower limit of current standard addition mud density under the actual working conditions. On the other hand, through the analysis of the wellbore pressure variation and its influencing factors when gas kick occurs, it was found that the variation of bottom hole pressure caused by gas kick was much smaller than that caused by tripping. Therefore, the surge pressure should be the main factor in the determination of addition mud density. Based on this, the determination method of addition mud density for each tripping section was proposed, which can calculate the addition mud density quantitatively and more reasonably for each tripping section based on the comprehensive consideration of factors such as wellbore pressure variation and formation pressure prediction error. The results showed that the current standards of addition mud density are too conservative in medium and shallow formations and may not meet the safety requirements in deep formations. • The surge pressure and its influencing factors during tripping were studied. • Current standards of addition mud density are too conservative in shallow formation. • The determination method of addition mud density for each tripping was proposed. [ABSTRACT FROM AUTHOR]

Effective well control depends on the drilling teams' knowledge of wellbore flow dynamics and their ability to predict and control influx. Unfortunately, detection of a gas influx in an offshore environment is particularly challenging, and there are no existing datasets that have been verified and validated for gas kick migration at full-scale annular conditions. This study bridges this gap and presents pioneering research in the application of fiber optic sensing for monitoring gas in riser. The proposed sensing paradigm was validated through well-scale experiments conducted at Petroleum Engineering Research & Technology Transfer lab (PERTT) facility at Louisiana State University (LSU), simulating an offshore marine riser environment with its larger than average annular space and mud circulation capability. The experimental setup instrumented with distributed fiber optic sensors and pressure/temperature gauges provides a physical model to study the dynamic gas migration in full-scale annular conditions. Current kick detection methods primarily utilize surface measurements and do not always reliably detect a gas influx. The proposed application of distributed fiber optic sensing overcomes this key limitation of conventional kick detection methods, by providing real-time distributed downhole data for accurate and reliable monitoring. The two-phase flow experiments conducted in this research provide critical insights for understanding the flow dynamics in offshore drilling riser conditions, and the results provide an indication of how quickly gas can migrate in a marine riser scenario, warranting further investigation for the sake of effective well control. [ABSTRACT FROM AUTHOR]