[en] The article deals with the method of evaluating oil equipment remaining lifetime by vibration diagnostics. The advantages of machine maintenance according to its technical condition, compared with planned-preventive repairs, are given. The technical conditions of the wellhead stuffing box of a beam pumping unit and a centrifugal pump machine were studied by Corsair vibration analyzer and Aurora software product, providing the evaluation of the current machine condition for planning a repair period. While analyzing the results of the equipment vibration diagnostics, the conclusions on faults were made and the dates of predictive maintenance were determined: the date for the next measurement (condition control) and the date for repair. The vibration diagnostics significance was confirmed in experiments as the most universal parameter which provides accurate information on equipment condition, making it possible to evaluate equipment technical condition in operation and predict its reliability. (paper)

[en] Revisions in the API 6A, 17th Edition, have resolved a number of long-term problems and expanded its scope and coverage of wellhead and christmas tree equipment. The 17th Edition, Feb. 1, 1996, represents the state-of-the-art in international requirements for wellhead and christmas tree equipment. The design, materials, and quality control aspects of API 6A have all been improved with an emphasis on making the document more acceptable around the world. However, there are unresolved issues that raise many questions about the future direction of efforts aimed at international standardization of wellhead and christmas tree equipment. Unfortunately, these unresolved issues confuse both manufacturers and companies purchasing this equipment. This ultimately increases wellhead and christmas tree costs, so it is to everyone's advantage to resolve these issues. This article describes the significant revisions that are included in API 6A, 17th Edition. Also discussed are the regulatory, standardization, and customer acceptance issues that cloud the future of API 6A, 17th Edition

[en] A new optical fibre feed-through for use in subsea in-well optical fibre sensing systems is reported. The new feed-through is compatible for use with standard subsea Christmas Tree penetrators and allows multiple re-mating of the feed-through over the lifetime of the device. The system has been extensively tested under in-well conditions and found to conform to the performance requirements. The new feed-through is planned to be used in one of the first subsea optical fibre in-well sensing systems

[en] This paper describes steps followed by PETROBRAS to carry out technological cooperation agreements with new suppliers of Wet Christmas Trees (WCT) in order to motivate the technological development of the WCT market and to reduce the costs related to the equipment. It deals with the technical aspects of the WCT designed by PETROBRAS and with the general characteristics of the agreements that are being negotiated with prospective suppliers aiming at the transference of the developed technology

[en] This paper describes the result of piping stress analysis for wellhead piping. The purpose of this piping stress analysis is to anticipate any over stress on the preliminary piping is a part of the flow line system and study the requirements of expansion loop on the piping. Pipe model starts at the wellhead as a fixed point and ends on the first guide at the corridor. Distance from wellhead to corridor is taken 100 m. Support type applied along corridor are rest support, guide support and guide support with U-bolt. Result of analysis indicate that stress that happened at wellhead is safe. (author)

[en] Previous studies using foam as a mobility control agent in partially depleted oil wells have shown that foam has a potential for enhancing oil recovery after primary water flooding. The characteristics of foam as indicated by the results of several studies point to three potential applications of foam in oil recovery processes. These are: Improving the displacement efficiency of gas-drive processes (mobility control). Improving the sweep efficiency of other fluid injection processes (mobility control and flow impediment). Restricting the flow of undesired fluids and plugging of high permeable oil 'thief' zones (partial or total pore blockage). (author)

[en] Short- and long-term aspects of measuring structural response parameters are addressed. Two specific examples of such measurements are considered for the purpose of illustration and in order to focus the discussion. These examples are taken from the petroleum industry (monitoring of riser response) and from the shipping industry (monitoring of ice-induced strains in a ship hull). Similarities and differences between the two cases are elaborated with respect to which are the most relevant mechanical limit states. Furthermore, main concerns related to reliability levels within a short-term versus long-term time horizon are highlighted. Quantifying the economic benefits of applying monitoring systems is also addressed. - Highlights: • Two examples of structural response monitoring are described. • Application of measurements is discussed in relation to updating of load and structural parameters. • Quantification of the value of response monitoring is made for both of the examples.

[en] Highlights: • Darcy-Stefan model is coupled with the porous elastic equation. • The spatial-temporal evolution of frozen/thawed interface in porous permafrost is investigated. • The predicted thawing subsidence around wellbore is very close to the measured. -- Abstract: A key challenge in Exploring oil and gas resources in permafrost regions is to predict the thawing subsidence of frozen soil around the wellbore. At present, the traditional thermo-hydro-mechanic (THM) model calculates thawing subsidence without actually considering the spatial-temporal evolution of the thawed-frozen boundary. The Darcy-Stefan model is used to describe the internal mobile interface problems in the heat transfer of saturated porous media due to ice/water phase transitions. In this paper, we established the coupling model of the Darcy-Stefan model and the elastic theory of porous media, including boundary conditions of heat transfer and Darcy flow on the moving boundary. The new model was validated through a series of small-scale examples and a test well in the Arctic region, which demonstrated the predicted subsidence amount of ground surface around the wellhead was in good agreement with the field test data. Further research indicated that with the increase of the thawing zone, the accuracy of calculation for the thawing subsidence could be significantly improved by using the THM model and considering the internal moving boundary. The models and conclusions in this paper can help design more reliable wellbore in permafrost regions throughout the expected life.

[en] In holography, quasinormal spectra of black branes coincide with the poles of retarded finite-temperature correlation functions of a dual quantum field theory in the limit of infinite number of relevant degrees of freedom such as colours. For asymptotically antide Sitter backgrounds, the spectra form a characteristic pattern in the complex frequency plane, colloquially known as the “Christmas tree”. At infinite coupling, the tree has only one pair of branches. At large but finite coupling, the branches become more dense and lift up towards the real axis, consistent with the expectation of forming a branch cut in the limit of zero coupling. However, it is known that at zero coupling, the corresponding correlators generically have not one but multiple branch cuts separated by intervals proportional to the Matsubara frequency. This suggests the existence of multiple branches of the “Christmas tree” spectrum in dual gravity. In this note, we show numerically how these additional branches of the spectrum can emerge from the dual gravitational action with higher-derivative terms. This phenomenon appears to be robust, yet, reproducing the expected weak coupling behaviour of the correlators quantitatively implies the existence of certain constraints on the coefficients of the higher-derivative terms of the dual gravity theory.

[en] Highlights: • A DBN-based methodology for dynamic risk analysis of SW fatigue failure during entire life is proposed. • Uncertainty in fatigue damage of SW is analyzed. • The most probable factors contributing to fatigue failure of SW are identified. • Active measures to mitigate the fatigue failure risk during SW's service life are developed. -- Abstract: Subsea wellhead is a critical component of the drilling and production system in offshore oil and gas industry. Excited by cyclical fatigue loadings due to environmental forces, the wellhead is prone to fatigue failure, which could lead to the loss of well integrity and even catastrophic accidents. Although fatigue failure probability of the wellhead carries an elevated uncertainties, it will definitely increase with the accumulation of fatigue in wellhead. This paper presents a fatigue failure risk analysis approach based on dynamic Bayesian Networks, aiming to predict the fatigue failure probability of the wellhead during service life. The proposed model can use the previously accumulated fatigue of the wellhead to probabilistically predict the present failure risk under present dynamic conditions. The practical application of the developed model is demonstrated through a case study. Adopting the predictive, diagnostic analysis techniques in the Bayesian inference, the dynamic fatigue failure probability of the wellhead at any time slices was achieved, and the most influential factors were figured out. Finally, the corresponding safety control measures are proposed to effectively mitigate the fatigue failure risk of subsea wellhead during service life.