Offshore Natural Gas Research Articles

Mass Transfer Study of Dehydration by Triethylene Glycol in Rotating Packed Bed for Natural Gas Processing

To ensure steady operation of gas transmission lines and meet the utilization specification of downstream processes, gas dehydration is employed in offshore natural gas production, where urgent demands for space and size exist. In this work, a rotating packed bed (RPB) was used to intensify the triethylene glycol (TEG) dehydration process and the effects of operating variables on the overall volumetric mass transfer coefficient (Kya) and height of mass transfer unit (HTU) were investigated. The value of HTU in a RPB was measured to be 4.3–7.9 mm, which was at least an order of magnitude lower than that in conventional columns, indicating the significant reduction in the size of the dehydration apparatus. The predicted Kya matches well with the experimental data, and the mean relative error (MRE) is only 6.68%.

Framework for work‐heat exchange network synthesis (WHENS)

Work and heat are the two predominant forms of energy in the process industry. Considerable savings can be achieved by synergizing the work and heat requirements of process streams. A generalized framework for integrating heat and work simultaneously is proposed based on a mixed‐integer nonlinear programing model for work‐heat exchange network synthesis. Starting with a set of streams with known flows, temperatures, and pressures, a network of single‐shaft‐turbine‐compressors with motors/generators, valves, heat exchangers, and utility heaters/coolers is synthesized for minimized total annualized cost. In contrast to existing works, (1) streams are not preclassified as hot/cold or high/low pressure, (2) pressure changes are allowed for streams with no net pressure change, (3) liquid‐vapor phase changes are allowed, and (4) phase‐based property correlations are used. Successful application of our approach to C3 splitting yields a nonintuitive configuration. Another application of an offshore natural gas liquefaction process is also studied. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2472–2485, 2018

Norway's role in the European energy transition

The EU has high ambitions for its clean energy transition. Reducing yearly CO2 emissions by 80% until 2050 requires large-scale implementation of renewable energy technologies and likely a large-scale electrification of non-energy sectors such as transportation. A major challenge imposed by renewable energy supply is the uncontrollable and intermittent nature of generation. Large flexibility volumes and capacities are needed to manage an energy system with high shares of renewables. Norway, with a large hydropower base and flexibility potential in its offshore natural gas transmission grid, can support the EU clean energy transition by providing much needed flexibility and controllability. This will require expansion of hydropower production and transmission capacity as well as altered management of gas export pipelines. To make these flexibility options available, market participants must be incentivized by new market designs and instruments that place higher value on flexibility and controllability.

Recovery of thermodynamic hydrate inhibitors methanol, ethanol and MEG with supersonic separators in offshore natural gas processing

In offshore natural gas (NG) production, hydrate formation is a big concern that can impact the production and even stop NG flow. In this context, the injection of Thermodynamic Hydrate Inhibitors (THIs) in wellheads is widely employed in order to avoid these undesirable problems on subsea flowlines to gas processing rigs. However, in the main three-phase high-pressure separator in the gas rig, THI losses for gas phase are significant, particularly when the adopted THI is volatile like methanol and ethanol. This work discloses a new supersonic separator (SS) THI recovery process – SS-THI-Recovery – that treats the gas effluent from three-phase high-pressure separator achieving four simultaneous results: (i) gas water dew-point adjustment (WDPA); (ii) gas hydrocarbon dew-point adjustment (HCDPA); (iii) production of C3+ (propane and heavier) liquids as LPG; and (iv) recovery of almost all THI which would be lost in the gas otherwise. The proposition employs a supersonic separator (SS) battery followed by an anti-hydrates separator (LTX), a liquid-liquid THI extraction step and auxiliary THI distillation. SS-THI-Recovery was evaluated with HYSYS 8.8 simulator using methanol, ethanol and monoethylene glycol (MEG) as THIs. Supposing that the THI in the gas phase would be totally lost along with the exported gas otherwise, with SS-THI-Recovery the losses of methanol, ethanol and MEG were reduced by 91.9%, 79.3% and 99.2%, respectively, and such recovery factors could be further improved by increasing water flow rate in liquid-liquid THI extraction. Such high THI recovery entails reduction of THI costs with make-up, storage and transportation. Additionally, SS-THI-Recovery process is simple, with low footprint, and of easy implementation even for non-volatile THIs like MEG. Furthermore, the produced NG is ready for commercialization, dismissing additional treatment steps, not counting the commercial value of LPG. Therefore, new SS-THI-Recovery process configures an innovative and profitable alternative for gas treatment and THI recovery on gas processing offshore platforms.

Design and Optimization of Pressurized Liquefaction Processes for Offshore Natural Gas Using Two-Stage Cascade Refrigeration Cycles

Because of increasing interests in offshore natural gas and due to limited deck space, simpler liquefied natural gas processes are necessary. The aim of this paper is to develop three pressurized liquefaction processes using two-stage cascade refrigeration cycles instead of the conventional three-stage refrigeration cycles. The proposed processes are CH4–C2H6, CH4–C2H4, and C2H4–C3H8 processes. Taking the specific energy consumption as the objective function, simulation based optimization is conducted for the three novel processes as well as two conventional cascade processes by a sequential search method. Optimization results show that the C2H4–C3H8 process is the most efficient one with a specific energy consumption of 0.2089 kWh/Nm3, 22% less than that of the conventional CH4–C2H4–C3H8 process. Moreover, a detailed thermodynamic analysis is carried out for the five processes. The thermodynamic analysis results confirm that the C2H4–C3H8 process presents the best composite curve match and the highest co...

The initial production test on offshore natural gas hydrate in the South China Sea: An overview

The initial production test on offshore natural gas hydrate in the South China Sea: An overview

The first offshore natural gas hydrate production test in South China Sea

ABSTRACT Natural gas hydrates (NGH) is one of key future clean energy resources. Its industrialized development will help remit the huge demand of global natural gas, relieve the increasing pressure of the environment, and play a vital role in the green sustainable growth of human societies. Based on nearly two decades’ studying on the reservoir characteristics in the South China Sea (SCS) and the knowledge of reservoir system, the China Geological Survey (CGS) conducted the first production test on an optimal target selected in Shenhu area SCS in 2017. Guided by the “three-phase control” exploitation theory which focused on formation stabilization, technologies such as formation fluid extraction, well drilling and completing, reservoir stimulating, sand controlling, environmental monitoring, monitoring and preventing of secondary formation of hydrates were applied. The test lasted for 60 days from May 10th when starting to pump, drop pressure and ignite to well killing on July 9th, with gas production of 3.09×105 m3 in total, which is a world record with the longest continuous duration of gas production and maximal gas yield. This successful test brings a significant breakthrough on safety control of NGH production.

Sensibility Analysis of Pre-cooling Cold Box Pipeline Blockage in DMR Liquefaction Process

As the key equipment of onshore and offshore natural gas liquefaction (LNG) plants, the performance of cold box influences operation reliability of the whole system. Due to the fact that the temperature of pre-cooling cold box is much lower, its pipelines can be blocked by the hydrates. In this paper, a dynamic model of dual mixed refrigerant (DMR) liquefaction process is established. The variations of gas-phase and liquid-phase plugging ratios are selected as disturbances to test the dynamic responses of the DMR liquefaction process. In addition, an experimental device of DMR liquefaction process is constructed to verify the accuracy of dynamic model. The results show that the process parameters from dynamic model agree well with the experimental data. When the plugging ratio of liquid-phase pipeline is more than 21.75% or plugging ratio of gas-phase pipeline is more than 29%, control structures of DMR liquefaction process fail.

Climate change, future Arctic Sea ice, and the competitiveness of European Arctic offshore oil and gas production on world markets

A significant share of the world’s undiscovered oil and natural gas resources are assumed to lie under the seabed of the Arctic Ocean. Up until now, the exploitation of the resources especially under the European Arctic has largely been prevented by the challenges posed by sea ice coverage, harsh weather conditions, darkness, remoteness of the fields, and lack of infrastructure. Gradual warming has, however, improved the accessibility of the Arctic Ocean. We show for the most resource-abundant European Arctic Seas whether and how a climate induced reduction in sea ice might impact future accessibility of offshore natural gas and crude oil resources. Based on this analysis we show for a number of illustrative but representative locations which technology options exist based on a cost-minimization assessment. We find that under current hydrocarbon prices, oil and gas from the European offshore Arctic is not competitive on world markets.

CO2 separation from offshore natural gas in quiescent and flowing states using 13X zeolite

To improve the efficiency of offshore natural gas exploitation, CO2 separation from offshore natural gas in quiescent and flowing states using 13X zeolite was studied systematically by examining the voidage, adsorption time, inlet velocity, adsorber diameter, temperature, and pressure. An adsorption purification model was established and validated based on the experimental data. In quiescent adsorption, the contact area between 13X zeolite and the gas mixture is the most important factor for evaluating the adsorption purification efficiency, and higher voidages in the range of 0.25–0.50 were favorable for gas adsorption. However, in addition to the contact area, the contact time is an important factor for flowing adsorption. The purification efficiency of flowing adsorption is highest at a voidage of 0.35. At this voidage, the pressure drop in the adsorber was 70Pa. The stabilization time for adsorption equilibrium decreased with increasing inlet velocity. As the adsorption time increased, the adsorption heat at different axial lengths of the adsorber tended to reach a constant value, while a symmetric adsorption heat curve was observed at different radial lengths. Toward the reduction of the energy consumption in the adsorption process, the optimum adsorber lengths for different diameters, temperatures, and pressures were determined. Adsorption purification was enhanced with increasing temperature. Further, it could also be improved by an appropriate pressure. Optimization of the adsorber structure parameters and regulation of the state parameters during the adsorption process are important for reducing energy consumption and improving the purification efficiency. The findings of this study serve asa guide for setting the purification parameters for CO2 separation from offshore natural gas in engineering applications.

Membrane Separation of CO2 from Natural Gas

Background: Raw natural gas, one of the most important fuel sources worldwide, contains high level of CO2, which must be removed to avoid problems like pipeline corrosion, compression cost and reduction of heating value. The three main technologies used to separate CO2 from natural gas include cryogenic distillation, amine absorption and membranes. Membrane technologies have various advantages especially for offshore platforms. In recent years, more and more membrane systems have been applied to large offshore natural gas upgrading projects. Two entirely different membrane processes can be applied to the separation of CO2 from natural gas: gas permeation membranes and membrane contactors. Keywords: CO2 separation, gas permeation membrane, membrane contactors, membrane plasticization, membrane technology, natural gas, pre-treatment systems.

An Offshore Natural Gas Transmission Pipeline Model and Analysis for the Prediction and Detection of Condensate/Hydrate Formation Conditions

An Offshore Natural Gas Transmission Pipeline Model and Analysis for the Prediction and Detection of Condensate/Hydrate Formation Conditions

European Union energy supply security: The benefits of natural gas imports from the Eastern Mediterranean

This paper analyzes the potential of Eastern Mediterranean offshore natural gas discoveries to increase EU natural gas supply security. It presents an overview of, the status quo of EU-28 natural gas import dependency, the efforts to increase energy security through various measures, and the challenges to supply diversification. It further provides an analysis of the energy and offshore resource sectors of Egypt, Israel, Cyprus and Lebanon. The paper presents projections of domestic natural gas consumption needs for the years 2012–2042 and results show that potentially large quantities will be available for exports. An empirical model is used to analyze the capital and transmission costs for exporting gas to Europe via the East Med pipeline. The East Med pipeline project is discussed in the broader context of other regional supply options as well as potential U.S. LNG exports to Europe. The paper concludes that the East Med pipeline, which has been classified as a project of Common Interest by the EU, should receive policy priority as its benefits in terms of security of supply go beyond those that can be captured in a competitive market, and the positive externalities that it provides justify a ‘security premium’.

An Offshore Natural Gas Transmission Pipeline Model and Analysis for the Prediction and Detection of Condensate/Hydrate Formation Conditions

An Offshore Natural Gas Transmission Pipeline Model and Analysis for the Prediction and Detection of Condensate/Hydrate Formation Conditions

Local content requirements in the petroleum sector in Tanzania: A thorny road from inception to implementation?

Tanzania has recently discovered huge offshore natural gas fields. This has led the Government to develop local content policies (LCPs) to increase job and business opportunities for nationals in the sector. We study the process behind the development of these policies and the positions of stakeholders. We find that although there is a positive view among domestic stakeholders of imposing such policies, there is much suspicion—to such a degree that it shapes their recommendations of which policies to include in the LCP. One reason is that the Government monopolized the policy development process and abstained from conducting a consultative process. Our findings suggest that future Tanzanian policy development should include in-depth consultations to maximize the decision maker’s knowledge base, add to the transparency of the process and manage expectations. This would also contribute to effective implementation and lessen tensions, conflicts and suspicion among stakeholders.

Succession of States Mathematical Algorithm for Incorporation of Unit Operation in iCON® Process Simulator Applied in Natural Gas Purification

Over recent years, incorporation of unit operation in industrial process simulators remains an intriguing area of research. This is especially applicable to natural gas plant aimed for CO 2 gas removal in offshore platform that is often accompanied with a number of unit operations, complicated configurations, non-standard operating conditions and high impurities content. In addition, it is highly desirable to link the natural gas purification unit with other pretreatment, dehydration and auxiliary equipments already implemented in the process simulators to constitute the entire process plant. Although research work has arisen in this area, the incorporation is particularly challenging for iCON® process simulator since it does not inherit the intrinsic capability to incorporate standalone models of additional unit operations. Nonetheless, the incorporation is of exceptional importance since the intrinsic physical property and thermodynamic databases of iCON® process simulator can be employed conveniently to determine heating value of the product streams. Therefore, in current research work, a mathematical model has been developed to describe the countercurrent hollow fiber membrane module, which has been integrated as an extension in iCON® through utilization of the export/import functions embedded within the Excel unit operation of the process simulator. Validity of the simulation model has been demonstrated through good accordance with published literature. It is found that by determining the separation mechanism via adaptation of the mathematical model, heating value of the purified product stream can be reflected directly in iCON® to evaluate feasibility of the entire process design in offshore natural gas purification platform.

Exergy Analysis of Monoethylene glycol recovery processes for hydrate inhibition in offshore natural gas fields

Gas hydrate formation is an issue in natural gas production. In offshore deepwater scenarios the situation is aggravated by the inaccessibility, salinity, low temperatures and high pressures. Monoethylene glycol (MEG) injection in well-heads is one of the used technologies for flow assurance in gas flowlines. Rich MEG is processed in MEG Recovery Units (MRU) to be recovered as Lean MEG returned to well-heads. In offshore rigs, besides determining energy requirements, the assessment of energy degradation is also important, which can be done by Exergy Analysis. In this work, an exergy formulation is developed and three technologies of offshore MRUs are assessed. Since exergy is a property that depends on the definition of a reference environment reservoir (RER), Exergy Analysis is performed via two RER approaches, both presenting consistent results. Approach #1 prescribes the usual standard atmosphere, with the addend that it is saturated by equilibrium with an infinite body of liquid water and MEG is in chemical equilibrium with air species. Since MEG is spontaneously oxidable, this entails very high exergy flows for MRU streams with MEG. As MEG is practically conserved, high exergy efficiencies result for all MRUs hindering their discrimination. Approach #2 prescribes also the standard atmosphere in equilibrium with liquid water containing MEG at infinite dilution, but not in chemical equilibrium with air. The MEG condition in MRU streams is now more akin with the MEG state in this RER, resulting that MEG streams have lower magnitude of exergy flow, leading to realistic exergy efficiencies that allow MRU discrimination. The underlying reason is that the input exergy flows now have magnitude comparable with exergy losses.

Experimental investigation of CO2 separation by adsorption methods in natural gas purification

CO2 separation for natural gas purification by the adsorption method was studied in detail using volumetric adsorption apparatus. The crystalline phase and microstructure of the experimental sample were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Micromeritics ASAP 2020 instrument. The XRD pattern proves that the experimental sample consists of 13X zeolites. The SEM images show that the 13X zeolites expose a large number of micro-channels on the surface of the particles. The microporous volume is 0.22cm3(STP)/g. The ideal swing frequency for the adsorption tank can improve the adsorption performance of an adsorbent compared with a static adsorption tank. The pure CO2 adsorption experimental data agrees well with the extended Langmuir model. The Langmuir-Freundlich model correlates the CO2/CH4 mixture adsorption experimental data fairly well. The relative errors between the simulated results and the experimental data are very little, which indicates that these fitted models are correct. The average selectivity of CO2/CH4 in a static and swing adsorption tank are, respectively, 3.57 and 3.93, considerably higher than 1, indicating preferential CO2 adsorption over CH4 in CO2/CH4 mixtures. This also shows that the swing can improve CO2 separation for natural gas purification. For the three types of motion status, the temperature of the adsorption tank increased in the order swing 2>swing1>static state for pure CO2 adsorption in 13X zeolites. The temperature variation decreased as the pressure increased. The amplitude and time of temperature variations in the adsorption tank can explain the adsorption capacity and adsorption speed. This research will improve the efficiency of offshore natural gas exploitation, and will affect the optimization of energy structures.

Canadian Arctic Offshore Oil and Natural Gas and European Union Energy Diversification: Towards a New Perspective?

Events shape and in turn are shaped by developments in Arctic ocean policy. Nowhere is this truer than of the ever-changing Arctic environment, which is in turn shaping and being shaped by a global demand for secure sources of future oil and natural gas supplies. As the polar ice cap progressively shrinks, and industry interest in the Arctic quickens, Canadians are confronting the challenges of developing their Arctic hydrocarbon resources. In Canada these conflicting objectives have led to innovative regulatory policies accommodating stakeholder desires on the one hand and environmental and economic considerations on the other. The European Union (EU) similarly has multiple objectives intersecting with its Arctic interests.

Design and optimization of offshore natural gas liquefaction processes adopting PLNG (pressurized liquefied natural gas) technology

Space limitation and energy consumption are two significant considerations for offshore natural gas liquefaction. This study designs three pressurized liquefied natural gas (PLNG) processes without CO2 pretreatment facility for natural gas containing less than 0.5% CO2, in which natural gas is converted into LNG at an elevated pressure (2 MPa), associated with a raised temperature (165.7 K). The three proposed processes, the cascade, the single mixed refrigerant (SMR) and the single expander PLNG processes, are simulated with Aspen HYSYS and optimized by the genetic algorithm (GA) to achieve the minimum specific power consumption. The cascade, the SMR and the single expander PLNG processes show an energy saving of 46%, 50% and 63%, respectively, compared to representative conventional liquefied natural gas (LNG) process. Moreover, the cascade, the SMR and the single expander PLNG processes present a smaller heat transfer area than representative conventional LNG process by 42%, 25% and 4%, respectively. In conclusion, the proposed PLNG processes can achieve both low energy cost and small footprint, providing a promising option for offshore natural gas liquefaction.