Deepwater Oil Research Articles

Study on a Circular Cylindrical Floating Device and Its Motion Response Characteristics

In this paper, a circular cylindrical floating device design is proposed by combining the structural features of the cylindrical Floating Production Storage and Offloading (FPSO) and the deep-sea Spar platform. It is suitable for deep-water oil and gas field development environment in the South China Sea. This floating device adds six floats with a Spar platform hard tank role based on the cylindrical FPSO to improve the buoyant center. This paper analyzes the motion response characteristics of the circular cylindrical floating device in waves by the Eulerian multi-phase flow model of STAR-CCM+. The results show that the pitch motion characteristics of the circular cylindrical floating device are better than those of the cylindrical FPSO and ship-type FPSO in the reference [8]. In addition, the paper also investigates the motion response of the circular cylindrical floating device with different directions of the incoming flow. The analysis shows that this floating device has the lowest motion response at 30° direction incoming flow. And the Response Amplitude Operator (RAO) of pitch motion shows a negative correlation with the incoming flow direction. The research results of this paper can provide a reference for the future development of marine resources, and have a certain practical significance.

Research on dynamic behavior vibration control of semi-submersible Marine platform based on ARID control system

As the development and infrastructure of deepwater oil and gas resources, the performance of the deepwater offshore platform is directly related to personnel safety, equipment safety, normal production and drilling process. Therefore, hydrodynamic calculation[1] and flow response-based control and optimization are current hot research topics. Semi-submersible marine platforms are widely used in the industry due to their large deck area, strong wind and wave resistance, and excellent mining ability. However, their complex and diverse lines in the marine environment result in a series of dynamic responses due to wave loads, particularly in the rotating dynamic behavior, which cannot be efficiently controlled using traditional vibration control methods.Many research studies have focused on developing efficient control systems to suppress the dynamic behavior of semi-submersible marine platforms. For instance, active mass dampers (AMD) and tuning rotational inertia dampers (TRID) devices have been used to control the translation dynamic behavior of the platform. However, their performance in controlling the rotating dynamic behavior of the platform is unsatisfactory.To address this challenge, this paper proposes a new type of active control system called the Active Rotary Inertia Driver (ARID), which utilizes an active torque control system to suppress the rotating dynamic behavior of the semi-submersible marine platform. The ARID system is developed based on AMD and TRID devices and aims to enhance personnel and equipment safety, as well as the normal production and drilling process of the platform.Therefore, this study presents a comprehensive review of the research status on hydrodynamic calculation and flow response-based control and optimization of deepwater offshore platforms, particularly the semi-submersible marine platform. The proposed ARID system is expected to contribute to this research area by offering an efficient solution to the rotating dynamic behavior of the platform.

Promotion and inhibition effects of wax on methane hydrate formation and dissociation in water-in-oil emulsions

Clarifying the effect of wax on hydrate formation and dissociation are important for the safe and high-efficient development of deep-water oil and gas fields. In this study, a series of experiments on the effect of wax on hydrate formation and dissociation in water-in-oil emulsions were systematically studied based on the variation analysis of temperature, pressure, torque, oil–water interface area morphology and water droplet size in emulsions. Microscopic images reveal that wax crystals form shell barriers on the oil–water interface, which increases transfer resistance, and the particle focused beam reflectance illustrates that the wax crystals decrease the water droplet size, which increases the oil–water interface area in emulsions. With increasing wax concentration, the hydrate induction time and growth rate show a bimodal shape because of the dual regulation of wax in emulsions, involving the inhibition effect of the transfer barrier layer and the promotion effect of the increasing water–oil interface area. The inhibition effect on hydrate formation was dominant when the wax concentration exceeds 6 wt%, resulting in a rapid decrease in both the growth rate and conversion ratio with increasing wax concentration. Compared with the bimodal shape of hydrate formation, the inhibition effect of wax on hydrate dissociation is the dominant regulation factor. The duration of complete hydrate dissociation by depressurization increased linearly with the increasing wax concentration, which increased the operation difficulty of hydrate plug removal. These experimental results provide valuable references for hydrate risk assessment and optimization of the project design of flow assurance for deep-water oil and gas fields.

Energy efficiency, sustainability, and operating cost optimization of an FPSO with CCUS: An innovation in CO2 compression and injection systems

Production in FPSO (Floating Production Storage and Offloading) is challenging due to its energy demand, operating cost, and environmental impact. In particular, the composition of the reservoir fluid, which varies along with the life of a well, greatly affects the operation and production of the FPSO. Any optimization study aiming at reducing energy consumption, sustainability, and operating costs during the life span of a well should take this fluid variability into account. Additionally, a typical FPSO operating in the Brazilian deep-water oil regions requires process fluid with high CO2 content. Therefore, a new FPSO process plant configuration comprises a membrane-based CCU (Carbon Capture and Utilization) system integrated with an MEA-based CCS (Carbon Capture and Storage) system and a CO2 compression unit with fewer compressors and one injection unit is proposed. Subsequently, automated optimization procedures consisting of a hybrid algorithm (NSGA-II + AfilterSQP) are implemented to optimize the energy efficiency, sustainability, and operation costs of the FPSO under consideration. More than 25 thermodynamic and structural design variables are considered as input variables in the optimization procedures. The results presented a significant reduction of up to 10.1% (2.9 MW) in overall power consumption, mitigation of CO2 emissions of up to 47 kg/h, a decrease of up to 3.9% (2.4 million USD/year) in operating cost, and an improvement of up to 53.5% in total heating and cooling demand of the FPSO, which means a reduction of 3.8 × 109 (kJ/h). In a proposed system with one CO2 injection unit, optimization results in the mitigation of total power consumption of up to 1.4 MW, a decrease in capital cost of 10 million USD, a reduction in operating cost of 50 million USD/year, and an increase of 4.4% in CO2 removal efficiency.

중국 지방정부 간 해상경계 설정에 관한 법적 고찰

Since the 1980s, China has witnessed rapid progress in its ocean-based industries, including fisheries and aquaculture, shipping, tourism, and deep-water oil and natural gas. Conversely this progress has continuously caused disputes between local authorities over marine planning and development. This is mainly because there are no boundaries on adjacent sea between local governments, which should be delimited based on law. In anticipation of the large-scaled exploitation of marine resources such as wind energy, oil and natural gas, will be more likely to cause maritime boundary disputes. The Chinese government recognizes the importance of maritime delimitation and introduced “Guidelines for Managing Maritime Boundaries” and a “Policy for Maritime Boundary Delimitation” in April 2002. They clearly stipulate the basic principles, procedures, considerations and dispute settlement system for maritime delimitation. Since June of the same year the Provincial governments began to delimit the maritime boundary. This study introduces background and current status of the delimitation of maritime boundaries between Chinese local administrations. Furthermore, this research evaluates the legal grounds of maritime boundary delimitation in China. At the end, this paper will put forth some implications for the Korean government to establish maritime boundaries for its local governments along with introducing laws on maritime delimitation.

Risk assessment of surface conductor jetting installation during deep-water drilling in sloping seabed

With the increasing exploration and development area of deep-water oil and gas fields in the South China Sea, well construction operations in the deep-water sloping seabed area become more and more frequent, so it is of great significance to accurately assess the safety of jetting well construction in the sloping seabed. Based on the characteristics of jetting well construction technology, the soil disturbance model was established and the wellhead instability mechanism in sloping seabed was studied. It was found that the jetting flow rate and fluid range were the main factors to determine the disturbance intensity and disturbance range to sloping seabed. The risk of jetting well construction in the sloping seabed was also studied based on the geologic models of various forms of sloping seabed. The finite element strength reduction method was used to analyze the influence of seabed dip angle, soil strength and soil stratification on sloping seabed stability, and the sloping seabed instability evolution law under different jetting disturbance parameters was obtained. Through the assessment of the risk of jetting well construction in the sloping seabed, the selection range of well locations was expanded, which could aid in ensuring the security of deep-water oil and gas field construction.

Integrated investigation on the nucleation and growing process of hydrate in W/O emulsion containing asphaltene

During the production and transportation of deep-water oil and gas, the low-temperature and high-pressure operating environment might induce hydrate formation and eventual blockage, which poses a serious threat to the flow assurance. Furthermore, the formation, aggregation and deposition characteristics of hydrate would become more complicated in the presence of asphaltene. Consequently, clarifying the effect of asphaltene on hydrate nucleation and growing process plays an important role in the safety production and flow assurance of deep-water oil and gas field. The kinetic characterizations of hydrate nucleation and growth in W/O systems containing asphaltene were investigated via experimental research, molecular dynamics simulations and mathematical modeling. Results revealed that the hydrate nucleation induction time increased with the increase of asphaltene content. The inhibition of hydrate nucleation by asphaltene in high-pressure (5 MPa) experiments was more pronounced than that in low-pressure (3 MPa). On the other hand, asphaltene restrained hydrate formation and the total gas consumption decreased with the increase of asphaltene content. The dynamic adsorption process of asphaltene at oil–water interface and the evolution of the surface coverage with time were elucidated by jointly solving the Ward-Tordai and Langmuir equation. Combined with the above aspects, the induction time model containing asphaltene was developed, which could provide a new perspective and methodology for deep-water flow assurance

Probability Prediction Approach of Fatigue Failure for the Subsea Wellhead Using Bayesian Regularization Artificial Neural Network

The subsea wellhead (SW) system is a crucial connection between blowout preventors (BOPs) and subsea oil and gas wells. Excited by cyclical fatigue dynamic loadings, the SW is prone to fatigue failure, which would lead to the loss of well integrity and catastrophic accidents. Based on the Bayesian Regularization Artificial Neuron Network (BRANN), this paper proposes an efficient probability approach to predict the fatigue failure probability of SW during its entire life. In the proposed method, the BRANN fatigue damage (BRANN-FD) model reflecting the non-linear relationship between the input and output data was developed by the limited fatigue damage analysis data, which was utilized to generate thousands of non-numerical fatigue damage data of SW rapidly. Combining parametric and non-parametric estimation methods, the probability density function (PDF) of SW fatigue damage was determined to calculate the accumulation fatigue damage during service life. Using the logistic regression, the fatigue failure probability of SW was predicted. The application of the proposed approach was demonstrated by a case study. The results illustrated that the fatigue damage of SW would be viewed as obeying the Lognormal distribution, which could be used to obtain the accumulation fatigue damage in operation conveniently. Furthermore, the fatigue failure probability of SW nonlinearly increased with the increment in the accumulation fatigue damage of SW, which could be helpful to ensure the operation safety of SW in deepwater oil and gas development, especially for aged wellhead.

Prediction method of solubility of carbon dioxide and methane during gas invasion in deep-water drilling

Gases that invade during deep-water oil and gas drilling may be concealed due to the gas dissolution effect, leading to increased well control risks. Accurate and rapid prediction of carbon dioxide and methane dissolution is of great significance for the prediction and control of wellbore pressure during gas invasion. In this study, 316 sets of carbon dioxide solubility data at 288.15 to 423.15 K and 0.1 to 100 MPa, and 266 sets of methane solubility data at 275.15 to 444.3 K and 0.1 to 68 MPa were used to train a machine learning algorithm. The machine learning prediction method for gas solubility was established with a support vector regression machine and a particle swarm optimisation algorithm. The kernel function and disciplinary parameters of the support vector regression machine were optimised using the experimental dataset. The solubility of CO2 and CH4 in water was measured using a gas solubility measurement device. The experimental and model analysis showed that the solubility of CO2 varied in different phase states. At a given pressure, the solubility of CO2 was highest in the liquid state, followed by the supercritical state, and then the gaseous state. The average absolute relative deviation percentages between the calculated values of the CO2 and CH4 solubility models and the experimental values were 2.57 and 8.20, respectively. The machine learning method is consistent with the high-precision Duan thermodynamic model for predicting the solubility of CO2 and CH4 in water and can be used to predict the gas solubility in deep water and deep oil and gas drilling.

Source-to-sink system and sedimentary characteristics of the lower Miocene submarine fans in the eastern deepwater area of the Qiongdongnan Basin, northern South China Sea

As the main target of deepwater oil and gas exploration, submarine fans are also the frontier and focus of sedimentology research. Based on the latest three-dimensional (3D) seismic data covering the study area, as well as heavy mineral, rare earth elements, and other data and guided by the theory of seismic sedimentology, this study analyzes the lower Miocene provenance system and sediment dispersion system in the eastern deepwater area of the Qiongdongnan Basin, northern South China Sea, from the perspective of source-to-sink system research. Our research defines the sediment supply function of provenance, paleogeomorphology and valley transport system, sedimentation results and distribution, and the coupling relationship between the source–channel–sink system and comprehensively constructs a set of application guidelines of source-to-sink system research to guide the exploration and prediction of favorable play in the study area and other similar basins. This study shows that in the early Miocene, as controlled by tectonics and paleogeomorphology, uplift areas developed on both the northern and southern sides of the Songnan, Baodao, and Changchang Sags in the Qiongdongnan Basin and small provenances of near-sag uplifts were found in the southern part of the sag. The provenance area in the northern part of the sag was large but not unified, and it formed different provenance systems consisting of the Hainan Uplift in the northern Songnan Sag, Hainan Uplift in the northern Baodao Sag, and Shenhu Uplift in the northern Changchang Sag. A series of canyon systems that developed in the early Miocene were the main channels for sediment transport from the shelf to the slope in the northern Songnan, Baodao, and Changchang Sags. In the early stage of the early Miocene, due to regional sea level decline, the scale of the canyons was generally large, and the scale of the canyons on the northern edge of the Songnan Sag was significantly larger than that of the Baodao Sag. As the relative sea level rose, the canyons became small, narrow, and shallow in the late stage of the early Miocene. Under the dual control of the “source–channel” system, multiple “delta–canyon–submarine fan” depositional systems developed in the Songnan, Baodao, and Changchang Sags in the early Miocene, and large deltas in the depositional systems were mainly located along the northern part of the sag and prograded to the shelf edge of the northern Songnan, Baodao, and Changchang Sags from north to south, providing a good material basis for the development of deepwater sediments.

Experiment-based coupled dynamic analysis of submerged production platform-mooring system in internal solitary waves

As a competitive alternative to the conventional dry tree and wet tree concepts, the next generation subsea production system, with a focus on the critical issues of well access and riser design, is designed to utilize shallow-water rated subsea production systems for the development of large oil and gas fields in deep and ultra-deep water. This study focuses on the crucial component of the next generation subsea production system, referred to as the submerged production platform-mooring system, and investigates its nonlinear coupled dynamic responses to internal solitary waves. A time-domain coupled dynamic analysis method is developed. Specifically, based on the load experiment in a large gravitationally stratified fluid flume, the applicability conditions of internal solitary wave theories and the determination method of hydrodynamic coefficients are quantitatively characterized, and the internal solitary wave load model for the submerged production platform is developed and validated. The fully coupled dynamic analysis model for the submerged production platform-mooring system is established and solved by the Generalized-α integration algorithm in combination with the Newton iterative method. The coupling effects, dynamic response characteristics, and security weaknesses of the submerged production platform-mooring system are analyzed. The effects of various key factors on the dynamic responses of the submerged production platform-mooring system are systematically analyzed. The results demonstrate that the dynamic responses of the submerged production platform-mooring system to internal solitary waves are characterized by the large amplitude surge and heave motions, and the significant fluctuation in the mooring tension, particularly when the submerged production platform is located at the density pycnocline. The developed method also has its applicability to the dynamic analysis of the deepwater free standing hybrid riser system in internal solitary waves.

Temporal and Spatial Relationships of Yellowfin Tuna to Deepwater Petroleum Platforms in the Northern Gulf of Mexico

AbstractIn 2006–2007, 110 Yellowfin Tuna Thunnus albacares were tagged with acoustic transmitters near deepwater oil platforms and one drillship in the northern Gulf of Mexico off the Mississippi River delta to determine the extent to which platforms act as fish aggregating devices (FADs). Vemco acoustic receivers were installed on six deepwater platforms to detect the presence of tagged individuals. Five of 12 Yellowfin Tuna captured in 2006 were detected in 2007, demonstrating multi‐year presence in the region. Ninety Yellowfin Tuna were detected in 2007, resulting in 221 platform residencies and 32 single detections. Duration of residence at a platform was positively correlated with the platform's depth, and the number of transitions decreased with platform‐to‐platform distance. In total, 109 movements between platforms by 46 (51%) different individuals were detected, traveling distances of up to 98.2 km. Yellowfin Tuna displayed interactions with deepwater platforms in the northern Gulf of Mexico similar to their interactions with FADs and other studied geological features, by way of aggregating or using them as meeting points, landmarks, and stopovers within a movement corridor. The large number of oil and gas platforms located in the northern Gulf of Mexico may have a significant effect on distribution, retention, and migration of Yellowfin Tuna populations in this area of the gulf.

A dynamic event tree for a blowout accident in an oil deep-water well equipped with a managed pressure drilling condition monitoring and operation system

Blowout is one of the most dreaded accidents for Oil and Gas companies. It is of particular concern during the drilling phase of deep-water oil & gas wells. This is due to the largely uncertain and extremely harsh environmental conditions that affect the design, drilling and operation activities of these wells. Seeking new technological solutions to prevent blowout has led, in the last few decades, to develop Managed Pressure Drilling (MPD) techniques.MPD offers many advantages compared to conventional drilling techniques, such as the capability (1) to detect the gas influx that initiates the kick that might lead to blowout and (2) to optimally control and circulate out this influx, to avoid the blowout. Nevertheless, effects of uncertainties on the MPD functionality are not fully understood and satisfactorily modelled within conventional safety assessment that relies on Event Trees (ETs).In this work, we propose a Dynamic Event Tree (DET) modelling framework of the scenario of kick escalation into blowout to allow accounting for the uncertainties that affect not only the kick variables, but also for the fundamental role played by the time and the delay of the kick detection task. The uncertainties affecting the kick variables are evaluated from kick events records taken from 2000 oil wells drilled in the Niger Delta, whereas the uncertainties affecting the time and delay of kick detection are evaluated by simulating the performance of the tool embedded into the MPD for kick detection (which applies the CUSUM statistical test to differential flow measurements), and assuming a possibilistic distribution for the confirmation time needed by the operator to take counteracting measures with respect to the evolving accidental scenario.A Hybrid Monte Carlo and Possibilistic method is utilized to represent and propagate uncertainties associated to the events occurring throughout the DET. Results are compared with those of a Purely Probabilistic method in support of the blowout probability quantification.

An [formula omitted]-cut interval based IF-importance measure for intuitionistic fuzzy fault tree analysis of subsea oil and gas production system

The subsea production system is very important for having deep water oil and gas production. The leakage of the oil and gas in the subsea production system may result in enormous adverse consequences on marine lives, high production loss, and serious deadly disasters to humans. For the safety analysis of subsea production system, importance measures play an important role to rank the components of the system according to their contribution to the leakage of oil and gas for preventive and corrective purposes. In conventional fault tree analysis and fuzzy fault tree analysis, various importance measures are developed for criticality analysis of the system. The objective of the present study is to develop a novel IF-importance measure by employing the concept of α-cut interval under intuitionistic fuzzy environment. The failure possibilities of basic events in fault tree analysis are quantified by triangular and trapezoidal intuitionistic fuzzy numbers. The presented research study applies α-cut intervals of intuitionistic fuzzy numbers, intuitionistic fuzzy fault tree analysis and interval arithmetic operations. The validation is carried out by comparing the developed importance measure with some pre-existing importance measures.

Molecular insights into methane hydrate growth in the presence of wax molecules

As a key issue emerged in the exploitation of deep-water oil and gas resources, the natural gas hydrates growth kinetics in waxy oil–water systems is still ambiguous. The microscopic mechanism of how wax affects hydrate growth needs to be elucidated. Molecular dynamics simulations were performed to explore the effect of wax molecules on methane hydrate growth in waxy oil–water-hydrate systems. The simulation results indicated that the different growth pathways of methane hydrate with wax molecules should be attributed to the changes in the mass-transfer process of methane molecules and the structural properties of interface water molecules. When n-heptadecane wax molecules (C17H36) were adjacent to oil–water interface, they inhibited hydrate growth by adsorbing methane molecules in the oil phase and preventing methane molecules from migrating to the water phase. The addition of methyl heptadecanoate wax molecules (C18H36O2) extended hydrate growth time to achieve a greater amount of hydrate formation by promoting the conversion of the water film between hydrate phase and oil phase into hydrate. In terms of the influence of wax crystallization, the co-crystallization of C17H36 and C18H36O2 hindered the mass transfer of methane molecules at the oil–water interface, which is due to the free space reduction after wax adsorption and the repulsive force between C18H36O2 and methane molecules, thereby slowing down the growth rate of hydrate. The dispersed C17H36 slowed down hydrate growth rate, while the dispersed C18H36O2 had almost no effect on hydrate growth rate. Thence, the microscopic analysis based on molecular dynamics simulations indicated that the effect of wax molecules on methane hydrate growth was complex, depending on the specific wax molecular structure and content of the wax.

Analytical study on the upheaval thermal buckling of sandwich pipes

Sandwich pipe is one of the most promising subsea pipelines for oil and gas transportation in deep waters due to its high-strength performance and thermal insulation. The gradient of the temperature distribution through the cross-section of sandwich pipes may be significant due to good thermal insulation of the core layer, so it is necessary to consider the temperature distribution in the upheaval thermal buckling analysis. In this study, analytical solutions are derived for the temperature distribution through the cross-section of a sandwich pipe by using the heat conduction equation, and they agree well with the results in the literature. Taking the temperature distribution into account, a mathematical model is proposed to simulate the upheaval buckling of sandwich pipes based on the von-Kármán type of geometrical nonlinearity and the Euler-Bernoulli beam theory. The coupled transverse and axial deflections of sandwich pipes are considered. The buckled section and the slip section are connected by the continuous boundary conditions. The force and moment resultants in the inner pipe, the core layer and the outer pipe are solved separately. Different material properties of different layers can be considered in this mathematical model. Semi-analytical solutions are derived and verified. The typical buckling process is analysed, and the forces, moments and stresses in different layers of sandwich pipes are discussed. Finally, several simplified models for the temperature distributions are proposed. The results show that the temperature distributions in the inner and outer pipes can be assumed to be constant and equal to the temperatures of the internal and external fluids, respectively.

Deepwater soil investigation using a free fall penetrometer

Free fall penetrometers (FFP) can improve the efficiency of deepwater geotechnical site investigations. This study investigates the derivation of geotechnical properties from piezocone FFP measurements in the upper 4 m of the seabed at a clayey site with water depths of ∼1500 m. Data analysis methods as commonly applied in cone penetration test (CPT) analysis were tested with strain rate normalization methods previously suggested for FFP analysis. The logarithmic, inverse hyperbolic sine, and power law approaches were applied for strain rate normalization. Strain rate effects appeared small for FFP cone resistance (with μ = 0.1 for the logarithmic and β = 0.06 for the power law approach), but were apparent. Undrained shear strength derived from FFP data matched overall the CPT results, using an N factor Nkt = 12. Undrained shear strength derived from excess pore pressure measured at the u1 position also yielded favorable results using N∆u _FFP = 6. Two soil behavior type classifications showed acceptable agreement between strain rate normalized FFP and CPT results.

The effect of eccentricity on the collapse behaviour of sandwich pipes

Sandwich pipes (SPs) with adequate strength performance and thermal insulation capacity have become an attractive choice for oil and gas transportation in deep water. The SP has a more complex structural configuration than the traditional single wall pipe. The fabrication process can induce eccentric behaviours of the pipe layers, influencing the external pressure resistance capacity. In this paper, a two-dimensional numerical model of eccentrical sandwich pipes under external pressure is developed using the finite element software ABAQUS. Experimental results are employed to calibrate the numerical models. The verified numerical model combined with a Python scripting program is employed to develop the parametric analysis models. The effects of geometric parameters, material properties, and interlayer friction coefficients with different eccentricities on the SP collapse behavior are investigated. The results show that eccentricity has a significant effect on the collapse of SPs. With the increase of eccentricity, the collapse pressure of SP decreases significantly. Based on the numerical simulations, the optimized design under different geometric parameters, material properties, and interlayer friction coefficients is proposed, reducing the eccentricity effect while optimizing the collapse strength of the sandwich pipe. The present results will support the design and engineering application of deepwater sandwich pipe structures.

Ram Performance and Hydraulic Modeling of Subsea Blowout Preventer Control System

Summary A subsea blowout preventer (BOP) system is critical in providing safe working conditions for drilling activities in deepwater oil exploration. However, performance evaluation of the shear ram BOP is still a challenge for the industry. In this paper, two aspects of BOP shearing capability are studied: The required shear force to cut the pipe inside BOP successfully and the time it takes to shear the pipe and close the well. A finite element model is used to calculate the maximum shear force of a typical drillpipe, while an analytical hydraulic model is proposed to calculate the BOP closing time. A case study is presented for estimating the emergency disconnect sequence time in a deepwater offshore scenario. It is assumed that the BOP control system is activated from the surface, employing an electrohydraulic multiplexed control device for closing the BOP and rapidly disconnecting the lower marine riser package (LMRP), thus preventing damage to both riser and wellhead.

The Influence of Hydrothermal Activity on the Long-Distance Migration and Accumulation of Hydrocarbons: A Case Study from the Y8 Area in the Songnan-Baodao Sag of Qiongdongnan Basin

The Qiongdongnan (QDN) basin in the northwestern South China Sea has been shown to be rich in petroleum resources and has significant exploration potential for deepwater oil and gas resources. Therefore, it is of great significance to clarify the gas accumulation process in the deepwater area of the QDN basin, specifically the Y8 area. In this study, fluid inclusion analysis, including the identification and localization of fluid inclusions under a microscope, laser Raman spectrum analysis and homogenization temperature (Th) measurement, reconstruction of the thermal evolution burial history, geochemical analysis, and typical seismic section analysis were comprehensively used to interpret the gas accumulation process of the Y8 area. The laser Raman spectrum analysis results of fluid inclusions verified the existence of methane and confirmed the hydrocarbon charging event in this area. However, the Th of fluid inclusions in the reservoir, the mixed compositions of hydrothermal compositions (H2S + SO2) and hydrocarbons (methane) in the fluid inclusions, and the low Tmax values of some wells in the Y8 area comprehensively confirmed that the coincidence of hydrothermal activity with the accumulation process affected the long-distance gas accumulation of the Y8 area. The hydrothermal activity was also confirmed by the presence of fluid diapirs in seismic profiles of the Y8 area. Furthermore, the hydrocarbon accumulation process was reconstructed using the modified thermal evolution history considering the effect of hydrothermal activity. Overall, this study attributed the high Th of fluid inclusions in the reservoirs of the Y8 area to hydrothermal activity and proposed a long-distance migration model of hydrocarbon accumulation coinciding with hydrothermal activity, both of which are beneficial to understanding the accumulation process of the Y8 area.