Deepwater Oil Fields Research Articles

Study on the mixed deposition rate and phase transition thermodynamic parameters of crude oil wax crystals and hydrates

Throughout the development of deepwater oil and gas fields, the occurrence of mixed deposition involving wax and hydrate is a prevalent phenomenon. To understand this process, researchers have explored the kinetics and thermodynamic behavior governing the co-deposition of wax and hydrates. It was observed that the Gibbs free energy change of hydrate increases with increasing pressure, while the entropy change experiences a decrease under heightened pressure conditions. The Gibbs free energy change and entropy change of wax crystal precipitation exhibit an increase with rising wax concentration. In a 100 mL sample of simulated crude oil containing 10 vol% moisture and 2.5 wt% wax, the rate of solid phase deposition measures 0.1126 cm3/min when the temperature drops from 61 °C to 2 °C. The results exhibit that the dispersion of wax crystals within the oil phase serves to inhibit aggregation phenomenon during hydrate formation and can be effectively used to inhibit hydrate deposition.

Main Challenges and Strategies to Develop Santos Basin Sub-Salt Fields, Deep water Brazil

Abstract Santos basin of Brazil is a hot area of oil and gas exploration and development in the world. Many sub-salt oil fields have been discovered in recent years. The reservoirs are mainly composed of microbial carbonate rocks with strong heterogeneity, which has developed a variety of storage space types. The fluid is complex with high gas oil ratio and CO2 content. The re-injection of produced gas brings uncertainty to the production performance and the stability of facilities. The project investment is huge due to many factors such as deep-water, deep buried and far away from the coastline. The complexity of reservoir and high investment of project make the economic and effective development of reservoir full of great challenges. This paper describes the development strategies of Brazil’s sub-salt deep-water oilfield and the main successful methods to maximize recovery and profits under uncertain conditions. It includes the following three aspects: (1) abundant information acquisition to reduce the main uncertainties; (2) development plan with robustness and flexibility to deal with potential risks; (3) multidisciplinary comprehensive research to evaluate reservoir mode and development mode.

Refined Prediction Method for Production Performance of Deep-Water Turbidite Sandstone Oilfield: A Case Study of AKPO in Niger Delta Basin, West Africa.

Deep-water oilfields frequently employ large or superlarge well spacing, leading to significant production dynamics influenced by reservoir factors. Traditional methodologies often disregard these influences, resulting in poor accuracy. Therefore, an enhanced prediction methodology rooted in reservoir characteristics is proposed. This approach introduces the dynamic relative permeability law as a bridge, capturing macroscopic oil/water movement within the reservoir. For the first time, it integrates production dynamics with key controlling reservoir factors, encompassing reservoir architecture, injection-production connectivity, and reservoir heterogeneity. The results indicate that (1) In deep-water turbidite sandstone fields with ultralarge injector-producer well spacings, the distribution of oil-water movement is primarily influenced by reservoir connectivity and heterogeneity. The injection water sweeping ability coefficient can quantitatively describe the water flooding capacity, with a strong negative correlation between the injection water sweeping ability coefficient and interwell nonconnectivity coefficient and reservoir homogeneity coefficient. This suggests that better reservoir connectivity or weaker heterogeneity results in stronger water flooding capacity, leading to a wider range of water flooding under the same injection volume. (2) For regions with strong water flooding capacity (injection water sweeping ability coefficient 0.30-0.80), the water-free production period is the main production stage, with a focus on improving the planar flooding conditions. For regions with poor water flooding capacity (injection water sweeping ability coefficient 0.00-0.10), the middle and late water-cut periods are the main production stages, with a focus on improving interlayer dynamic differences in the later stages. For regions with moderate water flooding capacity (injection water sweeping ability coefficient 0.10-0.30), the initial focus should be on expanding planar flooding, followed by a focus on improving interlayer dynamic differences in the later stages. (3) The dynamic relative permeability law, capable of comprehensively portraying the reservoir's influence on macroscopic oil/water movement, emerges as a rational choice for production performance prediction in such contexts. Our method can improve the accuracy, compared with traditional method without geographical factors, from 45% to 90% during water-cut rising stage and 31% to 81% during production declining stage. The high prediction accuracy (90%) observed in the AKPO oilfields underscores the method's efficacy in directing on-site optimization and adjustments for the development of deep-water turbidite sandstone oilfields.

Thermodynamically Efficient, Low-Emission Gas-to-Wire for Carbon Dioxide-Rich Natural Gas: Exhaust Gas Recycle and Rankine Cycle Intensifications

Onshore gas-to-wire is considered for 6.5 MMSm3/d of natural gas, with 44% mol carbon dioxide coming from offshore deep-water oil and gas fields. Base-case GTW-CONV is a conventional natural gas combined cycle, with a single-pressure Rankine cycle and 100% carbon dioxide emissions. The second variant, GTW-CCS, results from GTW-CONV with the addition of post-combustion aqueous monoethanolamine carbon capture, coupled to carbon dioxide dispatch to enhance oil recovery. Despite investment and power penalties, GTW-CCS generates both environmental and economic benefits due to carbon dioxide’s monetization for enhanced oil production. The third variant, GTW-CCS-EGR, adds two intensification layers over GTW-CCS, as follows: exhaust gas recycle and a triple-pressure Rankine cycle. Exhaust gas recycle is a beneficial intensification for carbon capture, bringing a 60% flue gas reduction (reduces column’s diameters) and a more than 100% increase in flue gas carbon dioxide content (increases driving force, reducing column’s height). GTW-CONV, GTW-CCS, and GTW-CCS-EGR were analyzed on techno-economic and environment–thermodynamic grounds. GTW-CCS-EGR’s thermodynamic analysis unveils 807 MW lost work (79.8%) in the combined cycle, followed by the post-combustion capture unit with 113 MW lost work (11.2%). GTW-CCS-EGR achieved a 35.34% thermodynamic efficiency, while GTW-CONV attained a 50.5% thermodynamic efficiency and 56% greater electricity exportation. Although carbon capture and storage imposes a 35.9% energy penalty, GTW-CCS-EGR reached a superior net value of 1816 MMUSD thanks to intensification and carbon dioxide monetization, avoiding 505.8 t/h of carbon emissions (emission factor 0.084 tCO2/MWh), while GTW-CONV entails 0.642 tCO2/MWh.

Development of a subsea distributed acoustic sensing acquisition system

Over the past few decades, distributed acoustic sensing (DAS) data acquisition has seen great improvements from better interrogators, engineered fiber, and lessons learned from subsea installation and acquisition. This has given us confidence that DAS cables can be installed in wells with subsea trees to be used as receivers for vertical seismic profile (VSP) seismic imaging. VSP imaging for deepwater fields has been demonstrated to provide better illumination and higher-frequency seismic data. Permanent DAS cable installation can be used to acquire highly repeatable time-lapse (4D) data. DAS cables have been installed in a number of subsea wells on two deepwater oil fields with the intention of covering the crest of these fields with high-frequency seismic data. A system has been developed to allow for DAS acquisition on these offshore subsea wells with long-distance tie backs using permanently installed interrogators on the floating platforms and engineered fiber in the wells. On each of these fields, a DAS cable has now been installed, and subsequently, a zero offset (ZO) DAS VSP has been acquired for verification and commissioning. These ZO DAS VSP acquisitions indicate high-fidelity installations resulting in DAS VSP data with excellent data quality. These first subsea DAS acquisitions indicate great promise, and further installations and acquisitions are planned with the ultimate goal of providing high-frequency seismic images over the crest of these fields to reduce the uncertainty in decisions around reservoir management and future infill drilling.

Optimization of subsea production facilities layout based on cluster manifold system considering seabed topography

High investment in deep-water development highlights the importance of optimizing the subsea layout, a properly optimized subsea production system reduces costs and contributes to production performance. Aiming at the minimum total construction cost of a subsea cluster manifold system, an integrated mathematical model considering the combination of subsea well grouping, cluster manifold layout, connection relationships, pipe routes and seabed topography is developed in this study. A modified adaptive particle swarm optimization (MAPSO) algorithm coupled with A-star algorithm, clustering algorithm and minimum spanning tree algorithm is used to solve the model by using a newly proposed process. The feasibility and practicality of the model is verified by designing the layout of a deep-water oil field, and the influence of manifold number and seabed topography is demonstrated by the difference in suggested cost. The model provides a new method which can be used to estimate costs more reliably.

Effect of asphaltenes on growth behavior of methane hydrate film at the oil-water interface

Investigation of the effect of asphaltenes, the natural surfactant in crude oil, on the methane hydrate formation is crucial for flow assurance in deep-water oil and gas field. However, most of recent studies on hydrate growth mainly focused on the impact of artificial and commercial surfactants. Limited attention has been given to the effect of the important natural surfactants presented in crude oil on hydrate film growth, such as asphaltenes. In this study, the influences of dissolved asphaltenes on the properties of oil-water interface and the growth of methane hydrate film were investigated. The morphology of methane hydrate film on the water droplet in the oil phase with different asphaltene concentrations was in-situ visualized in a visual autoclave equipped with microscopic imaging, and the lateral growth rate of the methane hydrate film was measured. The results showed that the addition of asphaltenes could increase the hydrophobicity of the methane hydrate film, inhibit the growth of hydrate, and change the morphology of the hydrate film. The growth rate of the hydrate film was negatively correlated with the asphaltene concentration (0–200 ppm), but stabilized above 200 ppm. In addition, this inhibition effect on the lateral growth rate was negatively correlated with temperature.

Study and Validation of a Novel Grouting Clamp Type Deepwater Oilfield Pipeline Repair Method Based on Computational Fluid Dynamics

In order to handle the corrosion of underwater production pipe sinks in deepwater oil fields, a non-solid phase silicone plugging agent, an external clamp, and an underwater injection tool are combined in this paper’s innovative pipeline repair technique proposal. The optimal main agent to curing the agent ratio for non-solid phase silicone plugging agents was found to be 100:25, which was achieved through an experimental examination of the curing process. The compressive and cementing strength changes in the curd plugging agent were disclosed by testing and evaluating the mechanical behavior of the plugging agent. In addition, the limits of the compressive and cementing strength were found to be 143 MPa and 11.6 MPa, respectively. Based on this, a computational-fluid-dynamics(CFD)-based analytical approach of the complicated flow field in a deep sea environment on the eroding impact of a plugging agent was developed. Through numerical simulation testing, the mathematical relationship between the plugging agent’s maximum pressure and the flow field’s velocity was established. The limits of saltwater and petroleum oil on the erosion of the plugging agent were found to be 4.19 MPa and 3.29 MPa, respectively, which are values that are far below their strength limits. In this way, the viability and efficacy of this novel pipeline repair technique were confirmed. The study presented in this paper sets the groundwork for an in-depth analysis and optimization of novel corrosion control solutions for deepwater oil field subsea process pipes.

A MINLP model for the layout design of subsea oil gathering - transportation system in deep water oil field considering avoidance of subsea obstacles and pipe intersections

This paper focuses on the layout design of subsea oil gathering-transportation system in deep water oil field. In such a system, subsea manifolds are applied to gather and transport the produced fluids from subsea wells to floating processing terminals. A mixed integer nonlinear programming (MINLP) model is proposed, constrained by a series of operation and production requirements, aiming to minimize the total layout cost. Through the model, the pipe line network topology structure which reflects the allocations among the subsea wells, manifolds and processing terminals, the routes of pipes, as well as the size of the facilities could all be figured out. Two key contributions are made through this work. First, avoiding pipe intersections and subsea obstacles are integrated simultaneously, making the proposed model closer to practical situations. Second, a decomposition strategy based on Delaunay triangulation and gradient descent is constructed, achieving high quality initial solution and stable iteration process. The results of case studies indicate the validity, feasibility and stability of the proposed model and the solution method. Besides, the effect of manifold numbers on the layout optimization result is analyzed through the model, indicating its flexibility in the layout design analysis.

Microstructural characterisation and micromechanical investigation of the heat-affected zone in multi-pass welding of 9Ni steel pipes

9Ni steels have been recently adopted in supercritical CO2 injection systems in deepwater oil fields. The manufacture of these reinjection systems involves multi-pass welding procedures, which produce an Heat-Affected Zone (HAZ) with a high heterogeneity level regarding the microstructural features and the local mechanical properties. An extensive microstructural and micromechanical characterisation was performed over the HAZ of three welded joints with different heat-input conditions to evaluate the effects of the reheating cycles and the welding parameters on the microconstituents. Light Optical Microscopy (LOM), Scanning Electron Microscopy (SEM) and Electron Backscatter Diffraction (EBSD) analyses were performed to identify microstructural features that correlate to the local mechanical responses evaluated through an extensive microhardness mapping. Regarding the Coarse Grained HAZ (CGHAZ), the highest microhardness values for all welding conditions are found at the Supercritically Reheated CGHAZ (SCR-CGHAZ), characterised by its refined microstructure and a quite low area fraction of coarse martensite laths. The Subcritically Reheated CGHAZ (SC-CGHAZ) and the Intercritically Reheated CGHAZ (IC-CGHAZ) – regions where wider martensite blocks and higher coarse martensite lath area fractions were observed – composed the softer zones of the microhardness map. It was also found that reheating at intercritical temperatures induces the formation of supersaturated fresh martensite and may contribute to retained/reversed austenite particles’ C-enrichment, which may degrade the mechanical properties at the IC-CGHAZ.

Numerical investigation and design of suction caisson for on-bottom pipelines under combined V-H-M-T loading in normal consolidated clay

The length-to-diameter ratio of suction caisson used as the foundation of the pipeline system in deep-water oilfields in the South China Sea is usually between 1 and 2. Suction caisson will bear combined V-H-M-T loading, including vertical force, horizontal force, moment and torsion from the upper manifold structure during pipeline installation and operation. The failure envelopes equation is generally used for caisson design, but existing equations are mainly suitable for suction caissons under combined V-H-M loading. This study uses a finite element numerical investigation to study the combined V-H-M-T bearing capacity calculation method. The torsion influences on vertical force, horizontal force, moment bearing capacity and combined VHM bearing capacity are discussed. The results showed that the primary function of torsion is to share the tangential force around the cylinder wall, which causes the VHM composite envelope surface of the suction caisson to decrease. This impact is quantified through regression analysis of the calculation results. The design method of suction caisson for on-bottom pipelines under combined V-H-M-T loading in normal consolidated clay is summarized.

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.

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.

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

Progress and prospect of CNOOC's oil and gas well drilling and completion technologies

Offshore oil and gas production has become an important growth pole to ensure national energy security. However, China's offshore oil and gas production is lack of key core technologies and weak in tool and equipment foundation and can hardly support the optimized fast development of important fields. To solve these technological difficulties, China National Offshore Oil Corporation (CNOOC) insisted on independent technological innovation and overcame a series of key core technologies through theoretical research and key technology research and test during the 13th Five-Year Plan. And the following research results are obtained. First, several key technologies are broken through, including efficient drilling and completion in the middle and deep layers of the Bohai Sea, offshore large-scale heavy oil thermal recovery, deep-water oil and gas field development, and high temperature and high pressure well drilling and completion in the South China Sea, unconventional oil and gas stimulation, and offshore emergency rescue. Domestic first independently operated ultra deep water giant gas field, namely “Deepsea 1” is successfully put into production, so that the leap from 300 m to 1500 m of water depth and from exploration to development is realized. Second, key tools and equipment are developed, such as logging while drilling and rotary steering drilling system, deep-water drilling surface conductor, underwater emergency killing device, and underwater wellhead Christmas tree, which promote the high-quality development of China's offshore oil industry. Finally, some suggestions are proposed as follows. In the future, CNOOC shall strengthen independent technological innovation, quicken the pace to deepsea oil and gas, and continue to research key core technologies for oil and gas reserves and production increase (e.g. continuous localization of drilling and completion technologies, equipment and materials in complex fields), commingled gas production and test and green energy transformation (e.g. geothermal energy), so as to make greater contributions to ensure national energy security and build a maritime power.

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.

Brief Introduction of Sand Control Completion Technology in Deepwater Oil and Gas Fields

Brief Introduction of Sand Control Completion Technology in Deepwater Oil and Gas Fields

A Prediction Method for Flow-Stop Time in Deep-Water Volatile Oilfields: A Case Study of Akpo Oilfield in Niger Delta Basin

Due to the difference in oil and water density, the wellhead pressure continues to decrease with water-cut rising in deep-water volatile oilfields. Once it is close to the lower limit, the production well will stop flowing. This phenomenon seriously affects the production and recoverable reserves. By taking the dynamic relative permeability which can reflect the macroscopic movement of oil and water in the reservoir as an intermediate bridge, production performance has been combined with dominant reservoir factors, including reservoir structure, reservoir connectivity, and heterogeneity. By the statistical analysis of actual data, this paper clarified the quantitative relationships between dominant reservoir factors and production performance and established the refined prediction methods for production dynamics including water-cut and liquid production rate. A prediction method for the wellhead pressure was further established, and the flow-stop time of single well can be accurately predicted. The results can be used in annual production forecast and recoverable reserve evaluation. This method had been successfully applied in Akpo oilfields in the Niger Basin. The results show that the production dynamics are significantly affected by reservoir factors in deep-water turbidite sandstone reservoir and the prediction method considering reservoir factors will be much more applicable. In deep-water volatile oilfields, the flow-stop risk of the production well in middle and high water-cut stages is very great and is mainly affected by the water-cut and liquid production rate. Judging from the application effect of Akpo oilfields, this method has high prediction accuracy and can be used to guide optimization and adjustment in deep-water oilfields.

Technical and Economic Feasibility Study for Implementing a Novel Mooring-Assisting Methodology in Offloading Operations Using Autonomous Unmanned Aerial Vehicles

Summary As oil and gas exploration goes toward deeper fields in the Brazilian industry scenario, offloading operations emerge as the most viable option to drain production. However, these operations demand expensive resources, such as shuttle tankers and support boats; operational risks, which despite being managed, limited, and mitigated to be as low as reasonably possible, are still present in some stages (i.e., ship’s approximation to the oil rig, mooring, hose connection, and so forth); and environment limiting parameters (i.e., wave height, surface-current direction, wind speed and direction, and so forth). Therefore, in this paper, we propose using unmanned aerial vehicles (UAVs) in an autonomous mode to carry out the messenger line from the shuttle tanker to the floating, production, storage, and offloading (FPSO) unit or the floating storage and offloading unit (FSO) instead of line-handling (LH) boats (for conventional operations that use those resources) or the messenger-cable-launching guns (for dynamic positioning operations). This represents a viable alternative solution to reducing costs and risks in these tasks and a possibility to eliminate some meteorologic and oceanographic limiting conditions to operations, because the UAV will be susceptible only to wind conditions, and not to sea and visibility conditions, like LHs are. We present the simulated results of the proposed methodology using a robotic operating system (ROS) and the economic gain [derived from cash-flow-cost reducing of operations, payoff time of the investment, net present value (NPV), and internal rate of return] of applying this technology, evaluating its use in a realistic scenario based on a real deepwater oil field in Brazil. The developed controller behaves very well, and simulations showed robust results. In addition, the economic study presents the proposal’s attractiveness.