Deepwater Drilling Research Articles

Effects of hydrophilic and hydrophobic nano‐CaCO3 on kinetics of hydrate formation

AbstractThe invasion of drilling fluids during well drilling through gas hydrate‐bearing sediments may seriously damage gas hydrate stability and distort well‐logging identification and evaluation in exploration and production of gas hydrate reservoirs. Adding nanoparticles into drilling fluids can be an efficient method to reduce fluid invasion. However, nanoparticles may induce hydrate formation in wells, which will block annulus and lead to safety accidents. Therefore, suitable nanoparticles used for hydrate drilling should be clarified first. This study addressed this issue by experimentally investigating the influence of hydrophilic and hydrophobic nano‐CaCO3 on CH4 hydrate formation in a dynamic system. We performed a series of experiments by using nano‐CaCO3 (1.0–6.0 wt%) with different particle sizes (20, 70, and 700 nm) at 3.0 °C and 6.0 MPa. The macroscopic kinetic parameters of hydrate formation were obtained. The results show that hydrophobic nano‐CaCO3 particles promote hydrate formation, while hydrophilic ones can inhibit hydrate formation at certain particle sizes and concentrations. This is mainly due to the different surface wettability, resulting in the different distribution of water and gas molecules in fluids. The hydrophilic nano‐CaCO3 with the particle size of 20 nm and addition of 3.0 wt% has the strongest inhibition effect under the given experimental conditions. In comparison with ultrapure water, the induction time is increased by about 38%, while the formation amount and rate are decreased by about 13% and 18%, respectively. This work will provide valuable ideas and references for the design of deepwater drilling fluid using nanoparticles, and also provide insight into revealing the formation and evolution mechanism of hydrate deposits at the micropore or even nanopore scale.

Development and sea trial investigation for deepwater drilling riser specialized soft hang-off system during transit

Offshore drilling activates have been significantly impacted by severe weather conditions as oil and gas development has moved into deep and ultra-deep water. Under the situation of imminent arrival of a typhoon, emergency retrieval of the whole drilling riser is time consuming and tedious. A novel specialized soft hang-off system to improve the adaptability of the drilling riser system under hang-off or transit operations is developed to solve the low-efficiency and time limitation for retrieval all drilling riser joints during extreme storm environment. The specialized soft hang-off system improves its bending capacity and reduce the risk of interference with diverter housing and moonpool and partially compensate the heave motion of drilling platform, to ensure the drilling riser keep lower tension and not compression during hang-off or transit mode. A numerical solution with mechanical model, boundary condition, results validation is conducted and transit operation window is obtained. Sea trial investigation on the novel specialized soft hang-off system during transit operation are conducted to evaluate the performance on global strength and dynamic load compensation effect. The research can be a significant basis and of valuable reference for deepwater engineering and the manufactured novel specialized soft hang-off system is an important emergency equipment.

Dynamic and quantitative risk assessment under uncertainty during deepwater managed pressure drilling

Risk assessment plays an important role in facilitating the safety and sustainability of deepwater drilling. Managed pressure drilling is increasingly used as an alternative to conventional drilling techniques. This technique increases the complexity and uncertainty of drilling systems with enhancement and advancement of functions. This paper presents a dynamic Bayesian network for risk assessment of managed pressure drilling. The method follows four basic steps including risk identification, topology construction, uncertainty characterization, and consequence evaluation. An event tree-fault tree model was established to develop potential accident scenarios and mapped into a Bayesian network to capture interdependencies and conditional relationships among the contributing factors. Both stochastic uncertainties and fuzzy uncertainties of risk factors are considered in the determination of failure probabilities. Degradation effects of equipment components are included in the forward reasoning of Bayesian network. The case study shows that the initial probability of the blowout is 2.28 × 10−5 and increases to 1.28 × 10−4 in ten time-intervals. Decision makers can take measures to prevent, eliminate, or mitigate accidents of deepwater drilling based on the evaluation results.

Performance of water-based drilling fluids for deepwater and hydrate reservoirs: Designing and modelling studies

In deepwater drilling, the properties of water-based drilling fluids change remarkably due to low temperature and high pressure, which have a significant effect on lost circulation, wellbore instability and the window between pore pressure and fracturing pressure. The present work investigates the influence of low temperature and high pressure on polymer and nanoparticle (boron nitride (BN)) based drilling fluids with an aim to improve their rheological properties and fluid loss control. The amplitude and frequency sweep tests were conducted to understand the viscoelastic nature of the samples. The amplitude sweep tests confirmed the structural stability of the designed fluid within the studied sweep frequency. The study reveals that storage modulus (Gʹ) and loss modulus (Gʺ) of the samples are enhanced with increasing concentration of BN nanoparticles. Their viscoelastic range also increases due to the intermolecular interaction within the structure of the fluid in the presence of the nanoparticles. Within the linear viscoelastic range (LVER), all the samples show the dominance of elastic modulus than viscous modulus which delineates the solid-like behaviour. The results of rheological tests of drilling fluid containing BN nanoparticles indicate a significant reduction in plastic viscosity (PV), yield point (YP) and apparent viscosity (AV). The rheological studies conducted at different temperatures (from 10 °C to −5 °C) and pressures (from 7.8 MPa to11 MPa) reveal the minimum effect of pressure and temperature on the rheology of samples, which are desirable for their applications in hydrate and deepwater drilling. The filtration loss experiments conducted at 30 °C and 0.69 MPa show a large reduction in fluid loss volume (60.6%) and filter cake thickness (90%) for the sample with 0.4 wt% BN nanoparticles compared to that of the sample without nanoparticles. The filter cake permeability is also in the favourable range with 0.008 mD which shows a 94% reduction compared to the sample without nanoparticles. A regression model was developed to mathematically describe the experimental results, which demonstrates a good fitting with the statistical data of fluid loss volume, thickness and permeability of the filter cake.

Propagation characteristics of Doppler ultrasonic wave in gas–liquid two-phase flow in an offshore deepwater riser

During offshore deepwater drilling, the strata with abnormal pressure are often encountered and gas invasion and overflow occur easily. If they cannot be detected and controlled in time, blowout may happen and even get out of control, which will cause considerable economic loss and irreparable casualties and may even damage the marine ecologic environment seriously. How to monitor overflow early during deepwater drilling is a global research hot, focus and difficulty at present. In order to provide theoretical guidance for the early monitoring of overflow in the riser during offshore deepwater drilling, this paper designed an experimental device for the early monitoring of gas invasion based on the propagation principle of Doppler ultrasonic wave. Then, the installation mode and angle of Doppler probe were optimized. Finally, the propagation of Doppler ultrasonic wave in the gas–liquid two-phase flow with a void fraction of 0–46% and a liquid flow velocity of 0–0.7 m/s was experimentally studied, and the change laws of Doppler ultrasonic wave with void fraction were revealed. And the following research results are obtained. First, when the void fraction changes, the signal voltage will jump up and down at different amplitudes and frequencies on the basis of initial curve. The signal voltage amplitude increases firstly and then decreases with the increase of void fraction. Second, when the increase amplitude of mean signal voltage caused by multiple reflection is greater than the attenuation degree of ultrasonic wave, the mean signal voltage increases. Otherwise, the signal voltage decreases. Third, the fitting curve of mean signal voltage scatters and void fraction under different flow velocities and void fractions during pump stopping and starting present a change law of quadratic function. In conclusion, void fraction can be quantitatively predicted based on the measured signal voltage, so as to provide guidance for the early monitoring of riser overflow and well kill operation during offshore deepwater drilling.

Dynamics of an offshore drilling tube system with pipe-in-pipe structure based on drift element model

Controllable dynamic behavior of an offshore drilling tube system is significant to secure the operation safety for deep water drilling. In the present work, a dynamic model of a drilling riser system is developed based on Hamilton's principle; and the corresponding finite element model is obtained via introducing the Hermite cubic interpolation function of a curved beam element. In order to consider the effect of the vibration of drill string on the dynamics of drilling riser, a new drift element model is proposed to describe the interaction between the riser and the drill string, and thus a coupled finite element model for the drilling tube system with pipe-in-pipe structure is developed according to the virtual work principle. The Newmark integral method is used to solve the mathematical model numerically; moreover, the obtained dynamic response of the pipe-in-pipe system is further verified and modified according to different collision states. The system dynamics are analyzed in both the frequency domain and the time domain, the vibration of the drill string is demonstrated to restrict the lateral deflection of the riser system; hence, for an actual offshore drilling tube system with pipe-in-pipe structure, it has stronger capacity of maintaining stability and reliability to overcome heavy ocean environmental loads. In addition, in order to effectively control the lateral deflection of the drilling riser, the strategy with high top tension and low buoyancy coefficient is suggested.

Theoretical and experimental research to remove hot water out of drill hose of deep hot-water drilling system

To date, hot-water drilling with its fast penetration rate is the most advanced technology to access rapidly subglacial environments through the thick ice in the Antarctica and Greenland. During deep hot-water drilling, it is important to remove the residual hot water from the drill hose when drilling stops; otherwise, the residual hot water in the hose will quickly cool down and be frozen in less than 1 h at −20 °C if no mitigation measures taken. The frost heaving force generated during the freezing will expand the hose and easily cause the hose to rupture. Based on prior experience and practice of water removal systems for deep hot water drilling, this study makes method choice and system design of removing hot-water from the drill hose, and theoretically calculates the minimum pressure of air pumping system needed to overcome pressure loss in the drill hose. Moreover, the indoor and outdoor tests are made to verify the calculations and provide a robust drill hose dewatering procedure.

Study on the Characteristics of Well Completion Technology in Deepwater Oil and Gas Field Development

In recent years, China has made certain achievements in shallow sea petroleum geological exploration and development, but the exploration of deep water areas is still in the initial stage, and the water depth in the South China Sea is generally 500 to 2000 meters, which is a deep water operation area. Although China has made some progress in the field of deep-water development of petroleum technology research, but compared with the international advanced countries in marine science and technology, there is a large gap, in the international competition is at a disadvantage, marine research technology and equipment is relatively backward, deep-sea resources exploration and development capacity is insufficient, high-end technology to foreign dependence. In order to better develop China's deep-sea oil and gas resources, it is necessary to strengthen the development of drilling and completion technology in the oil industry drilling engineering. This paper briefly describes the research overview, technical difficulties, design principles and main contents of the completion technology in deepwater drilling and completion engineering. It is expected to have some significance for the development of deepwater oil and gas fields in China.

The effect of oil-based drilling mud (OBM) on the assessment of hydrocarbon charge potential

Foundational to source rock assessment in exploration is an understanding of organic enrichment and hydrocarbon generation potential. With an increased use of oil-based drilling mud, particularly in deep water drilling, problems associated with contamination have complicated source rock assessment. Drilling fluid contamination is assumed to increase the apparent values of the basic screening source rock parameters such as total organic carbon (TOC) and total hydrocarbon generation (S1 + S2).It has been commonly assumed that the effect of contamination can be reduced or eliminated by pre-treating samples with organic solvents (i.e., extraction of the sample) prior to analysis. In this study, an attempt is made to characterize this extraction process on a suite of simulated cuttings samples that were contaminated and extracted prior to analysis to validate the assumptions presented in the literature.Results from these experiments show significant differences between values measured on the original and oil-based drilling fluid contaminated samples before and after extraction. After contamination and before extraction, measured TOC and Rock-Eval parameters indicate that the oil-based drilling fluids appear to be acting as an aggressive solvent, altering the apparent source rock potential. Contamination by oil-based drilling fluid appears to reduce the total organic carbon content and the residual generation (S2) potential, while increasing the free hydrocarbon content. This may be a result of the presence of solid bitumen or bituminite in the original sample, which are acted on by the oil-based drilling fluid. Following extraction of the contaminated samples, the TOC and residual generation potential undergo further reduction and the free hydrocarbons were nearly eliminated. It was also observed that uncontaminated samples, when extracted, experienced an increase in TOC and the S3 (CO2) peak. These increases may have resulted from the retention of small amounts of solvent.Unlike the common assumption in the existing literature, these data indicate that once oil-based drilling fluids contaminate a sample, pre-treatment extraction does not provide an accurate measure of either the original organic carbon or residual generation potential. The data indicate that the use of Rock-Eval pyrolysis results from extracted samples that have been contaminated by oil-based drilling fluid can result in a significant underestimation of the system's hydrocarbon source rock potential.

Modified Model for Shallow Soil Strength Recovery Calculation during Set-Up Periods of Jetted Conductor—A Case Study of Equatorial Guinea Bay Deep-Water Drilling

Jetted conductor setting depth is crucial for deep-water drilling. This paper presents an innovative method for determining the shallow soil resistance strength recovery factor based on the field data of Equatorial Guinea bay. It shows that the soil strength recovery factor of Equatorial Guinea bay is lower than that of the Gulf of Mexico. The conductor setting depth calculation referring to other place will have a high risk of wellhead sinking. According to the newly established designing charts, the conductor setting depth was recommended for the S1 well. Each preferred set-up period requires a specific setting depth. If the chosen set-up period is 2 days, the expected setting depth of a 36″ conductor should be 250 ft (76.2 m) and, similarly, 295 ft (89.9 m) for a 30″ conductor. The relationship between set-up period and surface conductor setting depth is established as well. Wellhead landed load appears to be the crucial factor for determining the conductor setting depth. The rationality of the newly developed shallow soil strength recovery model for the Equatorial Guinea deep-water block was also confirmed by the field data.

Wellbore Temperature and Pressure Field in Deep-water Drilling and the Applications in Prediction of Hydrate Formation Region

In the process of deep-water drilling, gas hydrate is easily formed in wellbores due to the low temperature and high pressure environment. In this study, a new, systematic, and accurate prediction method of temperature, pressure, and hydrate formation region in wellbores is developed. The mathematical models of wellbore pressure and transient heat transfer are established, the numerical solution method based on fully implicit finite difference method is developed, and the accuracy is verified by comparing with the field measured data. Combined with the hydrate phase equilibrium model, the hydrate formation region in wellbore is predicted, and the sensitivity effects of nine factors on wellbore temperature, pressure, and hydrate formation region are analyzed. Finally, the influence regularities and degree of each parameter are obtained. The increases of circulation time, geothermal gradient, displacement of drilling fluid, and injection temperature will inhibit the formation of hydrate in wellbores, and the influence degree increases in turn; the increases of wellhead backpressure and seawater depth will promote the formation of hydrate in wellbores, and the influence degree increases in turn. The changes of drilling fluid density, well depth, and hole deviation angle have little effect on the formation of hydrate in wellbores.

A Novel Method for Fracture Pressure Prediction in Shallow Formation During Deep-Water Drilling

Abstract Large numbers of deep-water drilling practices have shown that more than 60% of deep-water wells have complex leak-off during the drilling process, which poses great difficulties and challenges for the safety and operation time of deep-water drilling. The purpose of this article is to establish a method for predicting the fracture pressure in shallow formations. In this study, the deep-water shallow formation was divided into the upper unconsolidated soil layer, and the lower diagenetic rock layer according to the geotechnical distribution characteristics of the deep-water shallow formation. The location of the transition soil/rock layer zone was determined using the upper soil layer density trend line, and the lower rock layer density log data regression trend line. The deep-water shallow fracture pressure prediction model was established based on the soil/rock transition zone. The shear failure criterion was used above the transition zone, and the tensile failure criterion is used below the transition zone. The shallow fracture pressure of six drilled exploratory wells in the X block from the South China Sea was calculated using this new method and the calculation errors were all less than 3.18%. Moreover, the shallow fracture pressure body in this block was established using the Kriging interpolation method based on six drilled exploratory wells data. This shallow fracture pressure body established here was used to predict nine development wells shallow fracture pressure with a predictive error of less than 1.7% and there were no drilling accidents. The case study demonstrates that the new model can significantly improve the prediction accuracy has good prospects for popularization and application.

Prediction of methane hydrate formation conditions in salt water using machine learning algorithms

Predicting formation conditions of gas hydrates in salt water is important for the management of hydrate in processes such as flow assurance, deep-water drilling, and hydrate-based technology development. This paper applied and compared five machine learning algorithms to develop prediction tools for the estimation of methane hydrate formation temperature in the presence of salt water. These machine learning algorithms are Multiple Linear Regression, k-Nearest Neighbor, Support Vector Regression, Random Forest, and Gradient Boosting Regression. In total, 702 experimental data points in literature from 1951 to 2020 were collected for modeling purposes. The experimental data span salt concentrations up to 29.2 wt% and pressures up to 200 MPa. Among these five machine learning methods, Gradient Boosting Regression gives the best prediction with R2=0.998 and AARD = 0.074%. Thus, the methods of Gradient Boosting Regression function as an accurate tool for predicting the formation conditions of methane hydrates in salt water.

Energy efficiency prediction model and energy characteristics of subsea disc pump based on velocity slip and similarity theory

The variable-speed energy efficiency prediction model (EEPM) of subsea disc pump is the key to achieve double gradient in deepwater drilling, and it has also been the difficulty of pressure control matching and energy conservation. In this paper, the radial slip vortices are fully considered, and average slip method of circumferential velocity, relative velocity and absolute velocity at impeller outlet is proposed. Based on hydraulic energy loss and mechanical energy loss, the calculation method of theoretical head and similar parabola in similarity theory is improved, and EEPM is established. In addition, a new multifunctional test system and data processing model are designed to reduce the error. The experimental results show that the accuracy of EEPM is increased by about 4% when deviating from the rated speed by more than 20%, and the accuracy is about 99% within 20%. From the simulation, the flow passage is mainly a mixed-type movement, such as S-type double vortex and O-type single vortex. The turbulence kinetic energy near the volute tongue is the largest. The study improves the energy efficiency of drilling pressure regulation, and also provides a new perspective to the energy efficiency optimization and energy conservation of similar centrifugal pump and vortex pump.

The coupled model of wellbore temperature and pressure for variable gradient drilling in deep water based on dynamic mass flow

Variable gradient drilling in deep water is a new drilling method of using separators to separate hollow glass spheres (Referred to as HGS, it is the glass microbeads with low density less than 1.0 kg/m3, and the worse thermal conductivity) from the drill string directly into the annulus, which can form multiple gradients of drilling fluid density in annulus. This method can better deal with the problem of narrow pressure window in deep water drilling. At present, there are few studies on the wellbore temperature and pressure distribution of this technology, and the separation efficiency of the existing separator is too low to achieve variable gradient. The purpose of this paper is to develop a new separator to improve the separation efficiency, and to study the coupled wellbore temperature and pressure field of variable gradient drilling based on dynamic mass flow. Firstly, indoor simulated experiments were used to study the separation efficiency of the newly developed filter separator, and based on the separation efficiency, wellbore flow theory and the first law of thermodynamics, the dynamic mass flow at the location of the separator were fully considered. Considering the influence of wellbore temperature and pressure on thermophysical parameters, a coupled model of wellbore temperature and pressure was established based on dynamic mass flow. Then the model was discretized and solved by finite difference method and cyclic iterative algorithm. Further, this model was verified based on the existing models and drilling site data. Finally, the effects of key parameters in variable gradient drilling on the annulus temperature, pressure and fluid density were studied. The results show that the filter separator has high feasibility, and the separation efficiency can reach 95%–98.5%. Compared with conventional drilling, distribution curve of the temperature, pressure and the mixture density in annulus of the filter separator section has obvious inflection points in variable gradient drilling, and the number of inflection points is equal to the number of separators. What's more, the number and location of separators, the HGS volume fraction, pump flow rate, and the HGS density have significant effects on the annulus temperature and pressure. This research can significantly improve the feasibility of variable gradient drilling in deep water and provide a theoretical reference for further research in this direction.

New quantitative risk prediction method of deepwater blowout: Case study of Macondo well accident

ABSTRACT Risk assessment is an effective technology to prevent blowout accidents in deepwater drilling. In this paper, a new quantitative risk assessment method named Barrier-Index Risk Prediction (BIRP) method is proposed, which is based on the reliability analysis of safety barriers and risk index evaluation to predict the deepwater blowout risk, and the case of Macondo well accident is used for calculation and analysis. According to BIRP method, the deepwater blowout accident is the common result of the occurrence of the initial event (well kick) and the failure of deepwater well control system (consists of safety barriers), while the states of well kick and well control system is determined by their Risk Influence Factors (RIF). The parameter of risk Increment Range (IR) is introduced to calculate the deepwater blowout risk. Finally, the Early Risk Warning Signal of deepwater blowout is established to describe the blowout risk of target deepwater well. The analysis of control factors confirms the inevitability of Macondo well accident and the accuracy of BIRP method. BIRP method focuses on the impact of RIFs, and establishes the Risk Index Evaluation System to assign indexes for them to quantify their risk status; it pays attention to the cooperation and trust between human and machines, and can predict the blowout risk status of the target deepwater well in each stage of deepwater drilling & completion engineering in real time. The BIRP method is suitable for the risk assessment of deepwater blowout and can provide theoretical guidance for its safety management.

Developing a Thermally Stable Ester-Based Drilling Fluid for Offshore Drilling Operations by Using Aluminum Oxide Nanorods

Esters were found to be promising alternatives to oil, as a constituent of drilling fluids, due to their biodegradability and bioaccumulation attributes. In this study, we used ethyl octanoate ester (EO) as a low molecular weight synthetic oil for formulating an ester-based drilling fluid (EBDF). Aluminum oxide nanorods (nanoparticles) were introduced as a Pickering emulsion stabilizer. Like the commercial emulsifiers, they showed that they stabilized the invert emulsion drilling fluid in our study. The rheological and filtration properties of the EBDF were tested at normal pressure and three temperatures: low temperature deepwater (LT) conditions of 2.6 °C, normal pressure and normal temperature (NPNT) conditions of 26.8 °C, and elevated temperature conditions of 70 °C. To enhance the stability and filtration properties of the drilling fluid, aluminum oxide nanoparticles (NPs) were used. An optimum concentration of 1 wt% was found to provide superior rheological performance and higher stability than samples without NPs at NPNT, LT, and elevated temperature conditions. Steadier gel rheology was exhibited at elevated temperature conditions, and a slow rate of an increasing trend occurred at the lower temperatures, with increasing NP concentrations up to 1.5 wt%. Filtration loss tests presented a reduction of fluid loss with increasing the NP concentration. The results demonstrate that a reduction of up to 45% was achieved with the addition of 1 wt% NP. These results show that nano-enhancement of ethyl octanoate drilling fluids would suffice to provide a wider range of operational temperatures for deepwater drilling operations by providing better thermal stability at elevated temperatures and maintaining stability at lower temperatures.

Risk assessment on deepwater drilling well control based on dynamic Bayesian network

Deepwater drilling involves complex operations and equipment, so it is faced with various operational challenges including well control accidents. This paper proposes a dynamic risk assessment model for evaluating the safety of deepwater drilling operations. The dynamic risk assessment process includes three key steps: constructing fault tree models to analyze risk factors leading to a blowout accident, developing dynamic Bayesian network model based on the constructed fault trees, and performing dynamic risk analysis to evaluate the safety of well control operation. The proposed model includes risk factors about kick cause, kick detection, shut-in operation and kill operation, which covers the full process of a blowout. The proposed model could analyze the risk of blowout more comprehensively and the influencing degree of these four phases could also be clarified. Besides, the modular modelling method could update the structure and parameters of the developed model easily if new factors or data are added. The results show kick cause has the greatest impact on blowout accidents, followed by shut-in operation, kill operation and kick detection. Mutual information analysis and uncertainty analysis is performed to investigate the effects of risk factors on blowout. Finally, some corresponding preventive measures for blowouts are proposed.

Energy-efficient pressure regulation model and experiment of lift pump system in deepwater dual-gradient drilling

In order to improve the high-efficiency conversion between the pressure energy and the kinetic energy in the dual-gradient control of deepwater drilling, the energy-efficient pressure regulation model (EPRM) of the lift pump system (LPS) is established by energy efficiency prediction model of lift pump. Then the indoor and land-well similarity experimental platforms were designed. Indoor experiments show that when the deviation from the rated speed is more than 20%, the accuracy of the energy efficiency prediction model is improved by about 4%. The variable viscosity efficiency is more than 90% of the optimal from 40 m3/h to 75 m3/h, which shows that lift disc pump has good adaptability. Land-well experiments show that the average fluctuation error of inlet pressure is less than 5% with the flow change. During pressure regulation, the pressure fluctuation is less than 2.78%, and the minimum is 1.04%. In the pressure-increase and pressure-drop, the average pressure fluctuation is 1.445% and 2.02% respectively. For the pump with 2930 rpm, the regulation range should be controlled between 60% and 98% of the maximum speed, which can achieve more than 70% of the best efficiency. These make it possible to establish customizing targeted energy-efficient sections according to different actual drilling requirements.

Fragility assessment approach of deepwater drilling risers subject to harsh environments using Bayesian regularization artificial neural network

The drilling risers are the most critical and vulnerable connection of floating drilling platform and subsea wellhead. In order to improve the operation efficiency, the operators have attempted to suspend the drilling operations and keep the drilling risers connected to the wellhead to survive in the storm, thus the fragility of the drilling risers under storm is of paramount importance to drilling operations. This paper is aimed at proposing an efficient and robust BRANN-based non-intrusive approach for the fragility assessment of the deepwater drilling riser subject to storms. The proposed approach, which could effectively reflect the non-linear relationship between the input and output data, can generate thousands of non-numerical data under limited Finite Element Analysis (FEA) of the drilling risers, while the Monte Carlo Simulation (MCS) could be further incorporated to calculate the fragility curve. A case study was conducted to demonstrate the characteristics with respect to significantly computational reduction of the proposed approach compared to the conventional MCS method, and the proposed approach was verified to be robust and efficient in assessing the fragility of the drilling risers under storms. The related conclusions could be used to provide reference for operations of drilling risers under harsh environment.