Dynamic quantitative risk assessment of accidents induced by leakage on offshore platforms using DEMATEL-BN

On offshore platforms, oil and gas leaks are apt to be the initial events of major accidents that may result in significant loss of life and property damage. To prevent accidents induced by leakage, it is vital to perform a case-specific and accurate risk assessment. This paper presents an integrated method of Ddynamic Qquantitative Rrisk Aassessment (DQRA)—using the Decision Making Trial and Evaluation Laboratory (DEMATEL)-Bayesian Network (BN)—for evaluation of the system vulnerabilities and prediction of the occurrence probabilities of accidents induced by leakage. In the method, three-level indicators are established to identify factors, events, and subsystems that may lead to leakage, fire, and explosion. The critical indicators that directly influence the evolution of risk are identified using DEMATEL. Then, a sequential model is developed to describe the escalation of initial events using an Event Tree (ET), which is converted into a BN to calculate the posterior probabilities of indicators. Using the newly introduced accident precursor data, the failure probabilities of safety barriers and basic factors, and the occurrence probabilities of different consequences can be updated using the BN. The proposed method overcomes the limitations of traditional methods that cannot effectively utilize the operational data of platforms. This work shows trends of accident risks over time and provides useful information for risk control of floating marine platforms. Keywords: Offshore platform, DEMATEL, Bayesian network, Accident, Leakage, Quantitative risk, Dynami

Attribution of the Langshan Tectonic Belt: Evidence from zircon U–Pb ages and Hf isotope compositions

This study describes a previously unidentified Neoproterozoic mafic dyke emplaced in the northern flank of the Langshan Tectonic Belt. This dyke intruded into the micaquartz schist of the Zhaertaishan Group, and yielded an age of 908 ± 8 Ma. The youngest U–Pb ages of micaquartz schist from the Zhaertaishan Group in the Langshan area were 1118 ± 33 Ma, 1187 ± 3 Ma and 1189 ± 39 Ma, suggesting that the depositional age of the protolith of the schist was between 908 ± 8 Ma and 1118 ± 33 Ma. In addition, 436 U–Pb age data and 155 Lu–Hf isotopic data from six samples in the Langshan Tectonic Belt and one Permian greywacke from the Wuhai area show distinct differences between the northern and southern flanks of the Main Langshan area. The U–Pb ages of the northern flank are primarily Meso-Neoproterozoic; similar ages have not been identified in the southern flank to date. Moreover, two-stage Hf model ages of the northern flank feature three age peaks at ∼900 Ma, ∼1700 Ma and ∼2600 Ma; this differs from Hf model ages of the southern flank, which feature one strong age peak at ∼2700 Ma. These results suggest that the northern and southern flanks of the Main Langshan area have different geochronologic characteristics and should be divided further. Based on the U–Pb ages and Hf model ages, the northern and southern flanks of the Main Langshan area are named the North and South Langshan Tectonic Belts. Comparison of the U–Pb age and two-stage Hf model age distributions from the North Langshan Tectonic Belt, South Langshan Tectonic Belt, Alxa Block and the North China Craton (NCC) reveal that the North Langshan Tectonic Belt is similar to the Alxa Block and that the South Langshan Tectonic Belt is similar to the NCC. In addition, the zircon U–Pb age of 860 ± 7 Ma commonly observed in the Alxa Block was detected in the Permian greywacke from the Wuhai area of the NCC, which suggests that the amalgamation of the North and South Langshan Tectonic belts (i.e., the amalgamation of the Alxa Block and the NCC), occurred between Devonian and late Permian. Keywords: Langshan Tectonic Belt, Attribution, Alxa Block, North China Craton, U–Pb, Hf isotopic compositio

Modeling the Evolution of Major Storm-Disaster-Induced Accidents in the Offshore Oil and Gas Industry

Storm disasters are the most common cause of accidents in offshore oil and gas industries. To prevent accidents resulting from storms, it is vital to analyze accident propagation and to learn about accident mechanism from previous accidents. In this paper, a novel risk analysis framework is proposed for systematically identifying and analyzing the evolution of accident causes. First, accident causal factors are identified and coded based on grounded theory (GT). Then, decision making trial and evaluation laboratory (DEMATEL) is integrated with interpretative structural modeling (ISM) to establish accident evolution hierarchy. Finally, complex networks (CN) are developed to analyze the evolution process of accidents. Compared to reported works, the contribution is threefold: (1) the demand for expert knowledge and personnel subjective influence are reduced through the data induction of accident cases; (2) the method of establishing influence matrix and interaction matrix is improved according to the accident frequency analysis; (3) a hybrid algorithm that can calculate multiple shortest paths of accident evolution under the same node pair is proposed. This method provides a new idea for step-by-step assessment of the accident evolution process, which weakens the subjectivity of traditional methods and achieves quantitative assessment of the importance of accident evolution nodes. The proposed method is demonstrated and validated by a case study of major offshore oil and gas industry accidents caused by storm disasters. Results show that there are five key nodes and five critical paths in the process of accident evolution. Through targeted prevention and control of these nodes and paths, the average shortest path length of the accident evolution network is increased by 35.19%, and the maximum global efficiency decreases by 20.12%. This indicates that the proposed method has broad applicability and can effectively reduce operational risk, so that it can guide actual offshore oil and gas operations during storm disasters

Iron isotope fractionation during supergene weathering process and its application to constrain ore genesis in Gaosong deposit, Gejiu district, SW China

Fe isotope compositions of bulk samples from Gaosong ore deposit in Gejiu district, SW China were investigated and an overall variation in δ^56Fe values from − 0.33‰ to + 0.20‰ has been observed. In this study, the δ^56Fe values of primary sulfide ores are lower than the oxidized ores, while the iron isotope compositions of gossan samples, which represent highest oxidation degree, are heavier than the oxidized ore samples. These data indicate that iron isotopes experienced fractionation during supergene weathering process, furthermore, heavier iron isotopes enriched in more oxidized products. Another highlight is the Fe isotope compositions that are affected by mineralogy, which is considered as the primary mechanism of the large Fe isotopic variations in the primary ores. Enrichment of light iron isotopes in primary sulfide ores suggests that iron isotopes fractionated during fluid exsolution from its parental magma and the Fe source of skarn ores is mainly the magmatic source. This observation that significant Fe isotope fractionation occurs in supergene weathering process and fluid exsolution process provides an example in using Fe isotopes to trace supergene geochemical cycling and ore deposit formation/evolution processes

Ore microscopy & Fe isotope of the Xinqiao deposit and their constraints on the ore genesis

Systematical field work and ore microscopy studies have been carried out in the Xinqiao deposit. The fact that the skarn-associated magnetite is cut by the colloidal pyrite in the stratiform ore body provides a new constraint on the ore genesis of the stratiform sulfide ore body in Xinqiao deposit. The Fe isotope compositions of siderite minerals from the siderite ore bodies in Xinqiao and Fenghuagnshan skarn Fe-Cu ore bodies were analyzed and compared. Fe isotope compositions of the siderite from Xinqiao deposit are different from those from sedimentary and hydrothermal vein-type deposits, but similar to those from the Fenghuanghsan skarn Fe-Cu deposit. Moreover, the fact that the heavy Fe isotope enrichment in magnetite related to siderite and colloidal pyrite indicates that the siderite and colloidal pyrite cannot be altered to be magnetite. Fe isotope compositions in sulfide ores, quartz-monzodiorite stock and limestone wall-rock in Xinqiao strata bound sulfide and skarn ore were examined. The δ57Fe values of endoskarn and the earliest formed magnetite are lower than those of the quartz-monzodiorite, while δ57Fe values of limestone wall-rock are higher than those of the igneous stock. Moreover, such features as spatial and temporal zoning, evolution of Fe isotope are consistent with fluid exsolutionary and evolutionary theory, also accordant with basic theory of Fe isotopic fractionation, which suggests that two types of ores be resulted from the same hydrothermal fluid system and Fe element came from the same magmatic source. The Fe isotope characteristics, together with ore minerals paragenesis relationship, demonstrate that the Xinqiao Cu-S-Fe-Au deposit is a typical hydrothermal skarn deposit, rather than the multi-stage syngenetic-hydrothermal compound deposit

Discriminate between magmatic- and magmatic-hydrothermal ore deposits using Fe isotopes

Although discriminating high temperature mineral systems, for example, magmatic- vs magmatic-hydrothermal origin Fe deposits, is challenging, the emerging Fe isotope systematics have shown good potentials to provide crucial information on resolving the problem. Here, Fe isotopes of multiple types of samples from one iron oxide-apatite (IOA) deposit and two skarn Fe deposits are measured, aiming to study their behaviors in high temperature magmatic and magmatic-hydrothermal environments. The primary observation of this study is that magnetite samples from high grade ores of magmatic origin IOA deposits has a heavier Fe isotopic signature relative to the associated igneous rocks, whereas a lighter Fe isotopic composition in magnetite samples from magmatic-hydrothermal origin skarn deposits relative to the causative intrusions. Another distinctive feature is that δ56Fe values of the causative intrusions in the magmatic origin IOA deposits are lighter than that of non-fertile intrusions, whereas the ore-associated intrusions of the magmatic-hydrothermal deposit are heavier in δ56Fe than that of non-fertile igneous rocks. The above two observed scenarios suggest that Fe isotope fractionation exists in both magmatic immiscibility and hydrothermal fluid exsolution processes. Magma immiscibility leads to heavy Fe isotope enrichment in immiscible Fe-rich melt phase, and resulting light Fe enrichment in Si-rich melt phase. Hydrothermal fluid exsolution results in lighter Fe isotope enrichment in the exsolved liquid phase, with a heavy Fe isotope enrichment in the residual magma. Fe isotopes behave in different ways in magmatic and magmatic-hydrothermal mineralization processes, which makes Fe isotopes an effective tool to discriminate mineral deposits of magmatic origin from those formed by magmatic-hydrothermal processes

Oceanic redox condition during the late Ediacaran (551-541 Ma), South China

The late Ediacaran (551-541 Ma) oceanic environment could represent a significant preparation for the enrichment of redox sensitive elements during the early Cambrian and even for the evolution of life. However, the marine environment dur-ing the late Ediacaran has not been thoroughly characterized to date. To better understand late Ediacaran oceanic redox conditions, we investigated the Fe and S isotopic compositions of cherts from the slope (Yinjiang) and basin (Silikou) sections of the Nanhua basin in South China. The slope (Yinjiang) section is characterized by a wide range of delta Fe-56(T) values (-0.12 parts per thousand to 1.06 parts per thousand) and by continuously decreasing delta S-34(py) values from 40.4 parts per thousand to 4.1 parts per thousand. The variable delta Fe-56(T) values in the Yinjiang section primarily reflect the various oxidation degrees of dissolved Fe2+ in ferruginous seawater. The homogeneous delta Fe-56(T) signatures (0.02-0.40 parts per thousand) along the Silikou section and the decreasing trend of delta Fe-56(HR) values from 0.86 parts per thousand to near zero primarily depend on the mixing of Fe3+ hydroxide/oxide precipitates in a ferruginous water column, possibly followed by partial reduction, the authigenic framboidal pyrite trapped within an intermittent euxinic condition and detrital silicate Fe minerals. A 20-30%e discrepancy in delta S-34(py) values between the Yinjiang and Silikou sections may be ascribed to the formation of diagenetic pyrites and framboidal pyrites, respectively. Therefore, the continuously decreasing delta S-34(py) values in the Yinjiang and Silikou sections may reflect a significant increase of sulfate diffusion into sediments at the slope location and the enlarged marine sulfate reservoir at the basin location. These new results indicate that the deep water in the Nanhua basin is primarily characterized by a ferrug- inous condition with intermittent euxinic conditions in the basin location during the late Ediacaran. (C) 2018 Elsevier Ltd. All rights reserved

Multi-layer Long Short-term Memory based Condenser Vacuum Degree Prediction Model on Power Plant

A multi-layer LSTM (Long short-term memory) model is proposed for condenser vacuum degree prediction of power plants. Firstly, Min-max normalization is used to pre-process the input data. Then, the model proposes the two-layer LSTM architecture to identify the time series pattern effectively. ADAM（Adaptive moment）optimizer is selected to find the optimum parameters for the model during training. Under the proposed forecasting framework, experiments illustrates that the two-layer LSTM model can give a more accurate forecast to the condenser vacuum degree compared with other simple RNN (Recurrent Neural Network) and one-layer LSTM model

Zinc Geochemical Cycling in a Phosphorus‐Rich Ocean During the Early Ediacaran

International audienc