The cement between the casings and formation is a critical barrier element for ensuring zonal isolation. Shrinkage during curing and mechanical or thermal loads applied during production can compromise the cement and result in fluid migration paths such as micro-annuli. The fluid pressure inside the micro-annulus will cause elastic deformation of the channel walls. This deformation should be accounted for when developing methodologies for interpreting micro-annulus fluid leakage experiments and the application to real well conditions. Full-size test sections have been constructed with known cement defects and leakage properties to investigate barrier verification technologies. A micro-annulus test cell, instrumented with strain and pressure gauges, has been leakage tested. Leakage rates have been correlated to the micro-annulus size using a model coupling micro-annulus pressure to radial deformation of the cement and casing. The semi-analytical model and the predictions are compared to the experimental data. Within the regime of linear elasticity, the radial deformation of the cell wall is proportional to the pressure in the micro-annulus. During leakage testing, the pressure-driven radial deformation of the cell materials is coupled to the variation of the liquid friction pressure gradient along the axial length of the micro-annulus. The pressure gradient is greatest at the outlet of the micro-annulus. The models presented have been used to improve the interpretation of fluid flow during micro-annulus leakage experiments. An improved understanding of fluid leakage mechanisms through micro-annuli can be applied to field cases such as the interpretation and choice of treatment for sustained casing pressure build-up.
A subsea Blowout Preventer system plays an extremely important role in providing safe working conditions for drilling activities in deepwater oil exploration. However, estimating the performance of Shear Ram Blowout Preventeris still a challenge for the industry.
This paper considers different scenarios that may influence the shear capability of a typical subsea Blind Shearing Ram: the pipe size, ram shape, preload of pipe, off-center distance and tool joint of pipe. Element method analysis is conduct on the Abaqus software to calculate the maximum required shearing force for each scenario. Results of those simulations are collected and analyzed according to mechanic theories and oil field experience.
Furthermore, some recommendations are offered both in theoretical and practical aspects to build the criterion for the shear ability of a specific type of Blind Shearing Ram. Factors influencing shearing capabilities have been listed according to the result of the numerical simulation.
As the tendency of the offshore oil industry is going deeper and further, the subsea pipeline is exposed under tougher condition combining lower temperature with higher hydrostatic pressure. The severe condition creates a challenge towards flow assurance, which often results in a high cost solution. Reducing the cost while providing a qualified insulation performance is of great significance to deepwater development. For ultra-deepwater beyond 1500m, single-wall pipe usually fails to meet the flow assurance requirements or requires a huge amount of insulation material. Pipe-in-pipe configuration can provide a good insulation performance but comes with a high cost associated. Sandwich pipe is a new concept composed of two concentric steel pipes separated by a cementitious composite annulus that provides a combination of high structural strength with thermal insulation. It is reported to be a promising alternative for both flexible and rigid conventional pipes in applications for long distance pipelines. In order to further investigate its feasibility in deep waters, a subsea production system with depth at 2200m was used as a case study for a comprehensive evaluation of insulation performance of the sandwich pipe, including both steady-state and shut-in working conditions. For a comparative study, scenarios using single-wall pipe (SW), pipe-in-pipe (PIP) and flexible pipe (FP) were also considered separately. The results showed that (i) sandwich-pipe performs better in steady-state but worse in between shut-in and the restart period (ii) sandwich-pipe with larger diameter performs better than it with smaller diameter. The reasons for the sandwich pipe behavior were discussed and suggestions to improve the performance are presented.
Committee Mandate
Concern for crack initiation and growth under cyclic loading and unstable crack propagation and tearing in the ship and offshore structures. Due attention shall be paid to the suitability and uncertainty of physical models and testing. Consideration is to be given to the practical application, statistical description and fracture control methods in design, fabrication, and service.
Introduction
The advances addressing fatigue and fracture loading, fatigue damage accumulation, and crack growth approaches related to ships and offshore structures are reviewed and discussed by the 21st International Ships and Offshore Structures III.2 Fatigue and Fracture Committee. The rules and standards continued to be updated, accounting for the latest achievements in the field. The current committee report performed an in-depth update of the state of the art in this field with special attention on fatigue material properties, fatigue strength improvement, fatigue strength assessment based on rules (benchmark study A and B) and fatigue crack growth analysis in storm conditions (benchmark study C). The benchmark studies were performed by research groups originating from different Classification Societies, industrial partners, and universities as an essential contribution to the committee report. Fatigue and fracture is a vast developing field, and the committee report should be seen as a continuation of past International Ships and Offshore Structures III.2 Fatigue and Fracture Committee reports.
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