Deepwater Drilling Research Articles

Preparation of zwitterionic polymer and its application for dual-functional inhibition in deepwater drilling

During deep-water drilling operations, due to the conditions with low temperature and high pressure in the wellbore, methane hydrate can be easily formed in the presence of methane and plug the wellbore. In addition, the deep-water sediments are dominated by clay-silty with weak cementation, so well instability may be occurred due to clay hydration. In order to inhibit hydrate formation and clay hydration in deepwater drilling, a zwitterionic polymer AADV was synthesized through quaternary copolymerization of AM/AMPS/DMDAAV/VAC. The hydrate inhibition performance of AADV was evaluated in a high-pressure reactor chamber, and the results showed that AADV can delay the hydrate formation time from 330 min in pure water to 2204 min, indicating an excellent inhibition effect of hydrate formation. Meanwhile, 1 % AADV can significantly reduce the linear swelling rate of the calcium-based bentonite to 3.69 % for 10 h and increase the rolling recovery rate to 94.7 %, suggesting an excellent inhibition effect on clay hydration. The mechanism of dual-functional inhibition of AADV was further analyzed. The zwitterionic group in AADV and the hydrophilic amide group can strongly adsorb the water molecules through a strong hydration effect and the hydrogen bonding effect, respectively, which contributes to destroy the water molecules cage structure, and thus to suppress the hydrate formation. Besides, AADV can effectively obstruct mass transfer of methane molecules by increasing the viscosity of the aqueous phase and absorbing on the hydrate surface, leading to hydrate formation inhibition. For the inhibition of clay hydration, the SEM and XRD results proved that AADC inhibits the clay hydration through the film-forming effect. In addition, the contact angle of Na-Bent/AADC composite reached to 55.68° when the polymer concentration increased to 2 %, suggesting that the hydrophobicity of Na-Bent surface can be enhanced after AADC treatment. AADV can wrap around clay particles and form hydrophobic film through adsorption and intercalation, preventing the intrusion of external fluids and inhibiting clay hydration.

Research Progress onLeak Prevention and Plugging Technology in Deepwater Drilling

Abstract With the continuous development of global oil and gas resources, onshore and shallow water crude oil production is no longer sufficient to meet the demand. Therefore, deepwater oil and gas exploration and development have attracted high attention from various countries. China’s oceans are vast and rich in offshore oil resources, especially in the South China Sea, where oil and natural gas reserves are enormous. In recent years, it has become a key focus of national offshore oil exploration and development. The increasing complexity of deep-sea well leakage in the ocean and the increasing difficulty of management have brought great challenges to drilling construction and also caused significant economic losses. Therefore, the research on leak prevention and plugging technology for deep water in the ocean has become particularly important. This article investigates the current research status of deep water leakage prevention and plugging technology both domestically and internationally, discusses the main problems that exist in the development and drilling process of deep water oil and gas fields, analyzes the reasons for well leakage, and proposes corresponding solutions.

A novel damage index for crack identification of a drilling riser during deployment based on the modal vibration energy flow

Early detection of structural damage especially small cracks in marine deepwater drilling risers is of paramount importance. Small cracks are always hard to detect because of weak vibration signals if using traditional damage indices, such as natural frequencies and mode shapes including modal displacements, cross-section slopes, and curvatures. Especially when the deepwater riser is during deployment, the variable suspension riser length and strong sea environment noise make the small crack identification more difficult. To address this problem, this study formulates a new concept of damage detection by integrating the vibration energy flow theory into the vibration-based damage detection (VDD) technique. A novel damage-sensitive feature (DSF) named modal vibration energy flow (MVEF) is established for detecting and locating the small cracks in deepwater drilling risers. The capability of the approach is verified by using the same riser model and the numerical results in the literature. The sensitivities versus crack positions and depths, variable suspension riser length, and sea noise are studied in detail. Results show that the proposed index MVEF is more sensitive than the classic traditional DSFs, i.e., modal slope, modal strain (or curvature), and modal strain energy. In total, the MVEF approach can accurately identify the small cracks and is robust against noise interference, suitable for detecting and locating small cracks in the deepwater drilling riser during deployment.

Research on Nondestructive Testing Technology for Drilling Risers Based on Magnetic Memory and Deep Learning

Drilling risers play a crucial role in deepwater oil and gas development, and any compromise in their integrity can severely hinder the progress of drilling operations. In light of this, efficient and accurate nondestructive testing of drilling risers is paramount. However, existing inspection equipment falls short in both efficiency and accuracy, posing challenges to the sustainability of deepwater oil and gas exploration and development. To effectively assess the damage conditions of deepwater drilling risers, this study developed an inspection robot based on metal magnetic memory and researched intelligent defect recognition methods using computer vision. The robot can perform in situ inspections on drilling risers and has been successfully deployed for field application on a deepwater drilling platform. The application results demonstrate that this detection robot offers significant advantages regarding high reliability and detection efficiency. Utilizing data collected on-site, we constructed a dataset containing 1100 images that cover five typical types of defects in drilling risers, including pitting, groove corrosion, and wear. Based on this dataset, we proposed and trained a novel image classification model, SK-ConvNeXt-KAN. By deeply optimizing the ConvNeXt convolutional network incorporating the introduced SK attention module and replacing traditional linear classification layers with the KAN module, this model significantly enhanced its feature extraction capabilities and efficiency in handling complex nonlinear problems. Experimental results show that this model achieved an accuracy rate of 95.4% in identifying defects in drilling risers, which is significantly better than traditional methods. This achievement has dramatically improved the efficiency and accuracy of deepwater drilling riser inspections, providing robust technical support for deepwater oil and gas exploration and development sustainability.

Probability analysis method for well kick under uncertain formation pressure conditions

Drilling safety and efficiency are greatly impacted by kick, a major problem that is hard to diagnose, assess, and predict due to the complexity and high uncertainty of the deep water drilling formation pressure system. This article forms a pre-drilling well kick probability prediction method by establishing a calculation model for wellbore ECD and using the numerical solution method of Monte Carlo simulation algorithm. The bottomhole pressure uncertainty range gradually increases with well depth, according to simulation calculations, and the probability of a well kick decreases with drilling fluid volume. Theoretically, safe well control in deepwater drilling can be guided by the well-established kick diagnosis and formation pressure assessment techniques.

Parameter optimization based on deepwater drilling system simulation: A pre-salt exploration well in Brazil

The vibration of downhole drilling tools is the primary factor that limits the ROP of deep-water salt drilling. Pre-drilling modeling is an essential method for analyzing the dynamic characteristics of the drilling system. Currently, there is limited research on coupling models between the single riser model and drill string model in deepwater drilling dynamics, which hampers offshore drilling dynamics development. In this study, we integrated the dynamic riser model with the flexible drillstring dynamic model, optimized the system's boundary conditions through experiments, and established an advanced full-scale deepwater drilling system. Through virtual drilling simulation analysis and energy flow calculations of the drilling process, we investigated the movement trajectory of the drillstring system at different positions and its correlation with downhole vibration in deepwater drilling. Finally, we performed parameter optimization on Brazil exploration well salt formation. The results indicate that the rotational speed significantly influences the vibration intensity and motion state of both the drill string and downhole drilling tool. Moreover, the kinetic energy and strain energy of BHA effectively reflect the motion state of the downhole drilling tool. When drilling salt and salt intercalation in the Brazil exploration well, the WOB was controlled within 200 kN and 180 kN, and the rotational speed was controlled within 180 rpm and 140 rpm, respectively. This ensured optimal stability and minimized vibrations within the drill string system. The virtual simulation work based on deepwater drilling systems can provide guidance for designing and planning actual drilling operations, as well as proposing reasonable drilling parameters to enhance stability and ROP in the drilling process.

Hydraulic modeling study and control algorithm design of double-layer pipe dual-gradient drilling

Deepwater drilling has the problem of narrow safe density window, and double-layer pipe dual-gradient drilling is one of the effective ways to solve the narrow safe density window. Due to the different structure and process principle with MPD, there is an urgent need to establish the hydraulic model and control algorithm of double-layer pipe dual-gradient drilling in order to realize the normal regulation of bottom hole pressure during drilling. Based on the hydraulic theory of managed pressure drilling and considering the influence of the three-channel structure of double-layer pipe and the downhole hydraulic lift pump in double-layer pipe dual-gradient drilling, a hydraulic model of double-layer pipe dual-gradient drilling has been established and verified in land well tests. Based on the double-layer pipe dual-gradient drilling hydraulic model, a control algorithm based on pressure regulation and flow rate regulation is established considering the principle of double-layer pipe dual-gradient drilling process. The simulation results show that the control algorithm based on flow rate regulation can greatly reduce the bottom hole pressure regulation time by controlling the size of the flow rate of the return fluid. When the bottom hole pressure is increased from 25 MPa to 26 MPa, the regulation time is 11min, which basically meets the requirements of field operation. The hydraulic model and control algorithm of double-layer pipe dual-gradient drilling are favorable to the bottom hole pressure regulation during drilling and reduce the response time.

Exploring Machine Learning Techniques for Accurate Prediction of Methane Hydrate Formation Temperature in Brine: A Comparative Study

AbstractAccurate estimation of formation conditions plays a pivotal role in effectively managing various processes related to hydrates, including flow assurance, deep-water drilling, and hydrate-based technology development. The formation temperature of methane hydrates in the presence of brine greatly affects the efficacy and accuracy of these processes. This work presents a comprehensive and novel comparative analysis of nine distinct machine learning models for accurate prediction of formation temperatures of methane hydrate. This study investigated the application of major machine learning (ML) algorithms including multiple linear regression (MLR), long short-term memory (LSTM), radial basis function (RBF), support vector machine (SVM), artificial neural network (ANN), gradient boosting regression (GBR), gradient process regression (GPR), random forest (RF), and K-nearest neighbor (KNN). The model accuracy was validated against a large dataset comprising of over 1000 data points with diverse range of salt concentrations. In this regard, model accuracies were compared using several metrics including R2, ARD, and AARD. The experimental results exhibited KNN algorithm to be fast-converging, accurate, and consistent over the entire range of data points with an R2 score of 0.975 and AARD of 0.385%. The results enable efficient and accurate temperature estimation with ML algorithms for multiple hydrate-related processes.

Integrated methodology for safety analysis based on a system-theoretic approach and numerical simulation

The System-Theoretic Process Analysis (STPA) method is a recognized approach to system safety analysis. However, it still has inadequate capabilities for quantitative safety analysis. To overcome this limitation, an integrated methodology was investigated for quantitative safety analysis of the complex socio-technical system that combines a system-theoretic approach and numerical simulation. In the proposed methodology, STPA method is utilized to reveal potential unsafe control actions (UCAs) and corresponding causes based on the operational principle of the target system from systemic perspective. Moreover, the consequences of identified UCAs can be quantified and safety constraints also can be improved to prevent UCAs using numerical simulations. As a complex system, the blind shear ram preventers (BSRPs) in deepwater drilling activities, with tightly interacting diverse subsystems or components, is employed to illustrate the applicability of the methodology. The results verified that the proposed methodology could evaluate potential hazards and quantify the analysis results. These results will be helpful for the design and safe operations of the BSRP system. The developed methodology has the potential to be used for safety analyses in other process industries.

Study on reliability of control system in deepwater CBHP MPD system

Deepwater managed pressure drilling technology, with unique advantages in dealing with narrow density window, has been widely used in deepwater drilling operations. As the key equipment to realize managed pressure drilling, the control system in constant bottomhole pressure managed pressure drilling system plays an important role in drilling operations. In this study, a new reliability evaluation method based on fault tree analysis and dynamic Bayesian network model has been proposed to analyze the reliability of the control system. First, the structure of the control system in the deepwater managed pressure drilling system was analyzed to set up a fault tree model of the control system. Second, considering the influence of time on the reliability, a dynamic Bayesian network model of the control system was established. Third, the proposed model was partly verified using the verification method based on three axioms. Fourth, in consideration of the repair factor, the reliability and availability of the control system were calculated by using the exponential distribution model of failure time. Finally, the sensitivity of the control system was analyzed, and the mutual information, variance and entropy were calculated to find out weak links in key components of the control system.

Well Shut-In Pressure Determination Method for Deepwater Drilling Considering Fluid-Solid-Heat Coupling

Blowout is one of the most serious safety threats in deepwater drilling. Considering the characteristics of gas invasion in complex formations, gas migration and distribution, and dynamic changes in temperature inside a wellbore, a deepwater well-closing pressure determination method considering thermal-fluid-solid coupling was proposed. The model was verified using actual data, and the average error in the increase in casing pressure during the closing process was found to be 5.42%. The shut-in pressure of oil and gas wells under a transient shut-in process was analyzed. The results showed that the fluid thermal expansion caused by temperature recovery had a significant impact on the change in wellhead backpressure after well closure. Furthermore, the time required for the wellbore pressure to recover to the formation pressure varies nonlinearly with factors such as geothermal gradients, pit gains, bottom-hole pressure, and gas production indices. A pressure calculation chart was developed for deepwater drilling. The shut-in time for deepwater drilling should not be less than 15 min, and in cases where the gas production index is small and the bottomhole pressure difference is large, the shut-in time should exceed 90 min. The results can provide theoretical guidance and technical support for well shut-in processes during deepwater drilling.

Downhole detection of gas kick using low-frequency elastic wave: Multiphysics modeling and its implications

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.

Pemex’s Deepwater Ambitions Return

Pemex, Mexico’s state oil company, is laying the groundwork for a new round of deepwater exploration in the Gulf of Mexico in hopes to land a new elephant or two that could play a meaningful role in reversing the country’s downward production trajectory in the coming years. The company has seen its crude oil production cut in half since 2004 when production peaked at around 3.8 million B/D. By 2019, that number had fallen to nearly 1.8 million B/D. Levels have stabilized in recent years with the current estimate being just over 1.9 million B/D. Since taking office in 2018, Mexico President Andrés Manuel López Obrador has directed the operator to concentrate its drilling activity on less costly areas such as shallow water and onshore. Pemex is the world’s most indebted oil company with a debt load in excess of $100 billion. “We haven’t heard of any really large discovery recently,” said Diego Becerril, research manager, global analyst upstream team with Wood Mackenzie. “It’s been a couple of years since they last announced a giant discovery. They used to do it every year. “They were able to kind of control the production decline for a few years—2022 and 2023—I think by continuing to explore near areas that they already know, which in the end, doesn’t have that much prospectivity, but they can bring it online in a relatively short term and add volumes into the production portfolio. But moving forward they still need more resources. That is probably part of the reason we’re seeing a change of strategy going into deep water,” he said. The operator’s early deepwater exploration campaign in the mid-2000s was greeted with mixed results. The program yielded one known commercial gas discovery at Lakach. Other wells—Nab-1 (oil), Lalail-1 (gas), and Noxal-1 (gas)—all yielded hydrocarbons, but none of those finds were thought to be standalone development candidates. The debt burden has not prevented Pemex from planning more than $1 billion in investment in deepwater drilling to be conducted over the next several years. In February, hydrocarbons regulator CNH approved an updated plan for drilling in the Holok-Han area. The $400 million-plus investment plan follows 20 years of drilling in the area, during which 14 wells were drilled over that time—13 exploration wells and one delineation well—but no development plans emerged as a result of the program. The revised plan has Pemex drilling up to seven additional exploration wells in Holok-Han targeting Lower Eocene, Lower Pliocene, and Lower Miocene-aged reservoirs. CNH also approved plans for fresh drilling in the Perdido area. The $680 million program would see Pemex drill exploration wells in seven blocks near the US/Mexico maritime border and on trend with large finds on the US side. The bulk of the drilling would take place in 2026, likely utilizing Transocean drillship Deepwater Invictus, which will be under contract with Pemex for a 1,080-day period starting in late 2025. Pemex has identified more than 2 billion BOE in Perdido, according to CNH. The operator drilled 28 exploration wells from 2012 to 2019 in the area.

Dynamic analysis of a drilling string for deepwater riserless drilling with vortex-induced vibration considered

Riserless drilling will become the mainstream technology for deepwater drilling in the future owing to its operational characteristics. At present, researchers only analyze the seawater section or formation section but do not analyze the whole drill string to study the dynamics of riserless drilling. In fact, the ocean load affects not only the vortex-induced vibration characteristics of the drill string in seawater but also the load distribution of the drill string in the formation. Ignoring the formation or ocean load will lead to inaccurate prediction results. On this basis, in addition to the traditional drilling string boundary condition of seawater and formation, a new boundary condition of drilling string at mud line for riserless drilling is proposed. Considering vortex-induced vibration, a full-well drilling string dynamic model without riser drilling is established by the finite element method, and the dynamic characteristics of the full-well drilling string under multiple loads are analyzed. In addition, the effects of WOB, surface flow rate, and drilling fluid density on the dynamics of riserless drilling string in seawater and formation sections are discussed. This study provides theoretical guidance for the safety of riserless drilling in complex marine environments.

Research on Lateral Load Bearing Characteristics of Deepwater Drilling Conductor Suction Pile

The vast reserves of natural gas hydrates in offshore areas present significant challenges to development. Surface well construction technology is crucial for the extraction of deepwater natural gas hydrates. To ensure the safety of the subsea wellhead during the drilling process for deepwater natural gas hydrates, a novel conductor suction pile device has been designed, comprising a combination of suction piles and surface conductors. And research has been conducted to investigate the lateral stability characteristics of the conductor suction pile. Drawing upon the pile foundation load-bearing theory and the equilibrium of the differential element, a theoretical analysis model and corresponding governing equations of the conductor suction pile system are established. A solution for a multi-point boundary value problem by simplifying the conductor suction pile system into a two-end free beam is proposed. The governing equations are then converted into a first-order differential equation system, and the four-stage Lobatto IIIa collocation method program for the multi-point boundary value problem is developed and resolved using MATLAB 2023a. Furthermore, a case study of a well in the South China Sea elucidates the effects of wellhead load and seabed soil properties on the lateral load-bearing capacity of the conductor suction pile system, verifying the collocation method’s validity against the results from the finite difference method. After conducting a comparative analysis of the lateral load-bearing performance between conductor suction piles and traditional surface conductors, it is observed that conductor suction piles exhibit lower horizontal displacement and bending moments compared to surface conductors. Therefore, conductor suction piles demonstrate a substantial safety margin. The research findings provide a theoretical basis for the lateral stability of conductor suction piles during deepwater natural gas hydrate drilling. This offers a safe and efficient method for surface well construction in the extraction of natural gas hydrates.

Study of the Formation of Hydrates with NaCl, Methanol Additive, and Quartz Sand Particles

During deepwater drilling, testing, production, or hydrate mining, the circulating medium in the wellbore may contain solid particles, such as rock chips and sand, in addition to drilling fluids, gas, and water. In the high-pressure, low-temperature conditions of deep water, gas intrusion can easily combine with free water in the drilling fluid to form hydrates, increasing the drilling risk. Therefore, understanding the formation patterns of hydrates in drilling fluids is of significant importance for the prevention and control of hydrates. This study utilized a small-scale high-pressure reactor to investigate the impact of the stirring rate, NaCl, and methanol additives, as well as the sand content on the hydrate formation process and gas consumption. The results indicate that the hydrate formation process can be divided into an induction stage, a rapid formation stage, and a slow formation stage. The induction stage and rapid formation stage durations are significantly reduced under stirring conditions. In NaCl and methanol solutions, hydrate formation is inhibited, with the induction stage duration increasing with higher concentrations of NaCl and methanol. There was no apparent rapid formation stage observed. The final gas consumption decreases substantially with increasing concentrations of NaCl and methanol, reaching no significant hydrate formation at a 20% concentration. The sand content has a significant impact on the slow formation stage, with the final gas consumption increasing within a certain range (in this work, at a sand content of 20%), and being notably higher than in the pure water system under the same conditions.

A comprehensive prediction model of drilling wellbore temperature variation mechanism under deepwater high temperature and high pressure

Comprehensively considering the impact of properties of drilling fluid at high temperature and high pressure (HTHP), drill string eccentricity, rotation, and rock breaking of drill bit on the annular temperature profile, transient temperature variations were predicted by using a wellbore heat transfer model. The model was numerically solved using the finite difference method. Compared to DRILLBENCH simulations, the predicted model was more consistent with the field-measured data. The calculations revealed that comprehensively considering various heat source factors made the annular temperature closer to the actual wellbore value, with a temperature difference of up to 10.66 °C. When considering variations of properties of drilling fluid at HTHP, the lower section of the annulus showed a significant decrease in temperature with depth, with a bottom-hole temperature difference of 5.4 °C. The bottom-hole temperature decreased by about 2.6 °C from concentric to eccentric drill string, and the pressure difference was about 1 MPa. Compared to drill string eccentricity, rotation and rock breaking of drill bit had a greater impact on annular temperature, with bottom-hole temperature differences of 13 °C and 22 °C, respectively. Accurate temperature modeling can better understand and predict the variation patterns of wellbore temperature, providing important guidance for the development of deepwater drilling.

Research on the Influence of Deep-Water Drilling Risers on Drillstring Motion Trajectory and Vibration Characteristics

The swing of the riser in deep-water drilling can significantly impact the drill string. In this study, we establish a riser model that considers the combined disturbance of periodic dynamic wind and wave loads. By coupling it with the drill string model, we develop a dynamic model for deep-water drilling systems. Through analyzing multiple sets of different drilling parameters, we examine displacements and impact forces at various positions along the drill string system. Specifically, our focus lies on velocity, acceleration, and rotational speed information of BHA. We investigate how WOB and rotational speed influence motion trajectory and vibration characteristics of the drill string within the dynamic model of deep-water drilling systems. Simulation results reveal slight differences in whirling trajectories between inside the riser and below mud line for the drill string. Rotational speed has a greater impact on the drill string compared to WOB; higher rotational speeds lead to increased collision forces between the drill string system and both riser and wellbore. Our findings identify specific combinations of WOB and rotational speed parameters that can stabilize drilling operations within dynamic models for deep-water drilling systems. These research results provide valuable insights for adjusting WOB and rotational speed parameters in deep-water drilling.

Research on heat transfer law of multiphase flow in wellbore under coexistence of overflow and lost circulation in deepwater drilling

A reliable and accurate wellbore heat transfer model is essential for making critical decisions during deepwater drilling operations. This study develops a transient coupled flow model for the coexistence of overflow and lost circulation simulation in deepwater drilling. Through the established theoretical model, this paper studies the influence of gas influx, lost circulation, and coexistence of gas influx and lost circulation on wellbore temperature distribution and gas migration and analyzes the development of gas influx and lost circulation under different engineering parameters. The results show that the gas expansion after gas influx mainly occurs at the depth of 200 m and above. The gas void fraction is reduced with the increase of wellhead casing pressure, but the change range is gradually reduced. After the lost circulation occurs, the wellhead temperature, bottom hole temperature, and bottom hole pressure decrease obviously. The influence of the coexistence of gas influx and lost circulation on the change of wellbore temperature and pressure is greater than that of the two alone. The wellbore temperature under upper gas influx and lower lost circulation is generally higher than that under upper lost circulation and lower gas influx. However, the bottom hole pressure under upper gas influx and lower lost circulation is slightly smaller than that under upper lost circulation and lower gas influx.

Dynamic Analysis of A Deepwater Drilling Riser with A New Hang-off System

Dynamic Analysis of A Deepwater Drilling Riser with A New Hang-off System