Minimum Structure for Well Appraisal in Marginal Fields at 35m Water Depth without Jacket & Mudline Suspension System

ABSTRACT This paper proposes a minimum structure for drilling two appraisal wells. Conductors will be driven into seabed by a crane vessel or drilling-rig crane through a pre-installed lightweight guide-frame placed on seabed. After driving the conductors to required depth, the frame is raised and joined to the conductors at appropriate elevation by bolted and grouted connections. Six tie members connected between the frame and seabed by specially-designed small mat foundations will ensure stability of the structure against environmental loads. A small deck will be installed on the top of conductors to provide space for essential equipment required for prolonged well testing after departure of drilling rig. The platform will be accessed by small boats through a boat landing and ladder. In case of positive drilling outcome, a riser and flexible pipeline will be added to connect with the nearest subsea tie-in point. A detailed structural design of the minimum facility is performed to withstand omnidirectional environmental loads due to 10.0m high wave along with associated wind and current loads. Susceptibility of the structure against dynamic effect of wave loads is also investigated. Demonstration of structural adequacy against wave-induced fatigue loads and reserve strength against extreme environmental loads show the robustness of the minimum structure to perform against design environmental loads.

Evaluation of Residual Life of Existing Offshore Platforms in Western Offshore, India

Western offshore oil field in India has nearly 300 offshore platforms for oil and gas exploration, of which almost 50% of platforms have outlived their life. Life extension of these platforms has become essential for further production activities. In many cases, design level analyses combined with ultimate strength assessment, life extension has been granted. However, risk-based assessment based on the probability of failure based on available reserve strength linked to additional life extension could be a logical method. The Reserve Strength Ratio (RSR) is defined as a ratio of reserve capacity of the jacket structure and the design level environmental loads (1 year or 5year or 10 year or 100-year return period). The encounter probability of these design storms for the life extension period has been established probability for the extension period has been used as a threshold to determining the required RSR using the probability of collapse. For the present study, four typical aged wellhead platforms with different water depths are selected, and RSR is evaluated by carrying out push over analysis. The Monte Carlo Simulation method is used to generate the statistical values of RSR. The probability of failure is then calculated by First Order Reliability Method (FORM) using MATLAB for different RSR values. Reassessment criteria for the existing offshore platforms have been described from the reliability analysis results based on probability failure and encounter probability.

Evaluating Reserve Strength of Girder Bridges Due to Bridge Rail Load Shedding

This research experimentally and numerically evaluated the reserve strength of girder bridges due to bridge rail load shedding. The investigation included: (1) performing non-destructive field testing on two steel girder bridges and one prestressed concrete girder bridge, (2) developing validated finite element numerical models, and (3) performing parametric numerical investigations using the validated numerical modeling approach. Measured data indicated that intact, integral, reinforced concrete rails participate in carrying live load. Research results culminated in recommendations to evaluate the reserve strength of girder bridges due to the participation of the rail, as well as recommendations for bridge inspectors for evaluating steel girder bridges subjected to vehicular collision.

REDUCTION OF RISK DUE TO THE DESTRUCTION OF INDIVIDUAL AND UNIQUE TECHNICAL DEVICES

The article notes that reducing the risk due to destruction is possible by an a priori assessment of the maximum technical condition and the degree of degradation of the material of the technical device. The idea is to use a priori information about the technical condition and degradation processes that cause a decrease in strength and a decrease in resource. The application of numerical indicators of corrosion, corrosion resistance of materials, the degree of wear and reserve strength, defects, the risk of destruction and the effectiveness of technical diagnostics at any stage of the life cycle of a technical device is shown. The justification of the model of transition to the limit state is given. Numerical indicators of corrosion, corrosion resistance of materials, the degree of wear and reserve strength, defects, and the risk of destruction are applied. The possibility of developing recommendations for repair, strengthening or replacement of worn-out elements of individual and unique technical devices of various designs is shown.

Implementation of Advanced Offshore Structure Integrity Management based on API RP2SIM in Medco E&P Offshore

The structural integrity management (SIM) is important for the safe operation and maintenance of offshore fixed platform installation in accordance with the objectives set out in the Asset & Operating Integrity Philosophy. A Structural Integrity Program as part of the SIM is required as an ongoing process to ensure fitness-for-purpose of an offshore structure. Medco E&P developed the SIM system based on API RP2SIM in year of 2014 and has been successfully implementing it for the last 6 years. Based on this system, the interval of underwater inspection has been lengthened from every 2 years (time based inspection) into 4-10 years interval depend on the platform criticality. The potential cost saving of 70% is obtained as a result of implementation the underwater inspection for 10 years period based on inspection practices recommended in API RP 2SIM. The implementation of SIM process based on API RP 2SIM includes managing data, evaluation, strategy and program, the continuous improvement efforts and lesson learned. Medco E&P has implemented an advanced SIM program by determining the underwater inspection program based on risk based underwater inspection and consistently revisit and review the methodology; conduct the advanced analysis for reserve strength ratio; manage platform requalification; follow-up underwater inspection and repair; develop the integrated database system and the platform healthiness dashboard. The integrated database SIM System established a good practice for managing data record, data trending and data update since the system itself contains the platform of general information such as; the inspection data, inspection plan, structural analysis record, change record, reference document as well as the reporting tools. This dashboard is a combined status of initiatives, programs, implementation and evaluations that enables the integrity status can be accessed by management or other groups in the Company to promote effective communication and basis for decision making.

Comparative Study of Seismic Design and Performance of OMRF Building Using Indian, British, and European Codes

In India, damage cause by some major earthquakes, such as India/Nepal 2015, Sikkim 2011, Kashmir 2005, Bhuj 2001, Latur 1993, and Uttarkashi 1991, have raised alarms to professionals. The probability of seismic risk is higher in more densely populated Indian cities, such as Bhuj, Kashmir, Sikkim, Uttarkashi, as they come under the highest seismicity zone in India. Therefore, our primary interest is to investigate the seismic performance evaluation of the buildings in these seismic prone areas. Significant research has been conducted on the seismic performance of existing buildings. However, investigations on the seismic performance of a building with different country codes for the same earthquake event has not been explored, which is crucial in providing a deeper knowledge of the seismic performance of buildings. This paper presents a comparative study of an Ordinary Moment Resistant Frame (OMRF) building designed using three major codes, Indian (IS: 456-2000, IS: 1893-2002), British (BS: 8110-1997) and European (EC-2, EC-8). Six typical building models considered with earthquake (WiEQ), and without earthquake (WoEQ), and their assessments were interpreted using non-linear static analysis for determining their seismic performance. Seismic performance is compared in terms of base shear coefficient (BSC) and drift ratio that shows WiEQ models, at the drift ratio of 1.5%, the BSC was as follows; 0.78, 0.88, and 0.96 for the models designed for British, Euro, and Indian codes, respectively. The results show that the building models, that have been designed for the Indian codal provisions for both cases, performed well as compared to the other country codes. Base shear and drift ratio are the vital parameters that vary considerably among the building models. This aspect of the Indian code makes it a safer design methodology with higher reserve strength and a reasonably good displacement capacity before reaching the Collapse Prevention (CP) performance level.

Behaviour of partly stiffened cold-formed steel built-up beams: Experimental investigation and numerical validation

To address the various instability problems in cold-formed steel members, many researchers have mainly focused on developing innovative sectional profiles wherein geometry of the section plays a vital role in enhancing the inherent resistance of such sections against premature buckling. However, the process of forming such innovative shapes is not only complex and time-consuming but sometimes such sections fail to mobilize their complete reserve strength. Hence, a stiffening arrangement of weaker zones for mobilizing the untapped reserve strength is suggested. The contribution of this simple, effective and partly stiffening arrangements, aimed at eliminating/delaying the premature local buckling, is studied both experimentally and numerically and also compared with existing codes. Experimental study was carried out on different simply supported cold-formed steel beams with judiciously proposed stiffening arrangements under four-point loading. An equivalent hot-rolled steel beam was also tested to compare the efficiency of the cold-formed steel beams. The cold-formed steel beams investigated had different width-to-thickness ratio, different geometries and different stiffening arrangements. The test strengths, failure modes, deformed shapes, load versus mid-span displacements and geometric imperfections were measured and reported. The test strengths of the beam models are also compared with the design strength predicted by North American Standards and Eurocode for cold-formed steel structures. To validate the test results further, a numerical study was carried out on such stiffened cold-formed steel beams using finite element software ABAQUS. All these results show that the proposed strengthening system is efficient and economical and allow cold-formed steel beams to reach greater load carrying capacity.

On the Robustness of Earthquake-Resistant Moment-Resistant Frames: Influence of Innovative Beam-to-Column Joints

Background: The deformation capacity of beam-to-column connections strongly influences the robustness of earthquake-resistant Moment Resistant Frames (MRFs) when subjected to a loss-of column scenario. As a consequence, with the aim of foresee the structural response up to the failure, an accurate modelling of the ultimate behaviour of the joints is needed. Objective: In this paper, the influence of the connections on the behaviour of MRFs under a loss-of-column scenario has been analysed considering an accurate modelling of the joints. Method: In addition, in order to achieve this goal, different beam-to-column joints designed for seismic actions and tested at the Salerno University, have been modelled and introduced in a case-study structure, whose response has been evaluated by means of push-down analyses. In particular, the connections analysed and modelled are of three different types: a dog-bone connection, a partial strength Double Split Tee (DST) joint and a partial strength connection with friction dampers. Results / Conclusion: The results of pushdown analyses performed by means of SAP2000 computer software have been examined with the aim to determine the Residual Reserve Strength Ratio (RRSR) index that, combined with the energy balance method proposed by Izzudin et al. (2008), allow to assess the structural ro-bustness.

Nonlinear RPD Analysis of Jack-Up Rigs Including Material Plasticity

Rack Phase Difference or RPD may occur during the installation phase of a jack-up rig when it is jacking up at a location. Instances of failure of leg members of a jack-up have been reported in the past. Therefore, this is an important design issue. Among the many causes of high RPD, important ones are when one of the jack-up spudcans becomes eccentrically supported on the bottom or has lateral offset due to preexisting soft spots in the soil during installation. The resulting moment and shear on the leg is carried essentially by the horizontal guide reactions that may induce high stresses leading to failure of a diagonal brace in extreme cases. In a previous OMAE paper written by the authors [1] the importance of a 3D model of the jack-up that uses non-linear analysis methods by including large deformations and rotations was highlighted. In this paper it was also emphasized that the meaning of RPD has to be understood properly in relationship with moment or shear carrying capacity at the spudcan for a given jack-up. The present paper includes material plasticity effects in addition to the other nonlinearities in the 3D analysis to investigate the failure mechanism of a critical brace. Both applied moments due to the vertical load eccentricity at the spudcan and lateral displacement effects of it are considered. The behavior of a trussed leg jack-up depends heavily on the bracing pattern, chord and bay spacing as well as the size of the braces. For a well-designed jack-up the reserve strength beyond the initial exceedance of the allowable limits of member stress following the codes to the actual physical failure is considered to be important. This reserve strength could prevent actual damages to the rig. This paper discusses these aspects using one particular jack-up as example. The particular jack-up has shown very high RPD and reserve strength when a brace fails due to a large spudcan moment being applied or base deflection. The failure of the brace, however, does not indicate that the ultimate strength of the rig has been reached which is expected to be much higher. Although the analysis is for one particular jack-up, it discusses the parameters that in general could make the reserve strength large indicative of good design. These observations and the overall methodology of analysis used here could be beneficial to other rigs.