PSI - Issue 14

Praveen Bhat et al. / Procedia Structural Integrity 14 (2019) 656–663 Praveen Bhat, S. Karunanithi/ Structural Integrity Procedia 00 (2018) 000 – 000

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• Required pile segments for the new location shall be fabricated separately. • Fabricated plinth framing shall be taken to the new location and secured with skirt piles. • Transport the decommissioned jacket structures by cargo barge to the identified locations for installation. Modifications required if any, shall be carried out on the barge. • Jacket shall be installed at the new location. • Refurbished deck structures shall be brought to the new location along with the refurbished transition pieces for installation and minimum deck elevation to be ensured for relocations sites where water depth is slightly higher (up to 3-4m) than the original condition and where plinth platform is not feasible to be installed. • Elevation of associated appurtenances shall be adjusted to the new location as per the requirement. 3. Relocation Methodology For relocation of existing jacket platforms to new locations at different or similar water depths in western offshore of India, a general philosophy for foundation design has been developed in the form of: 1. Installation of plinth platform for relocation to field where water depth is higher than existing one. 2. Installation of insert piles and extra clamp-on skirt piles, if required, where water depth at relocation is similar to existing water depth for the platform.

Fig. 1. Proposed Plinth Platform for relocation to new field.

It is proposed to fabricate and install plinth platforms at the new locations, for significant difference of water depths between existing and new locations (Figure 1). The plinth platform will be then secured to the sea bed by driving new piles. The existing jacket structure shall be refurbished and strengthened, if required, at the barge and then shall be mated with the plinth platform. The topside will then be mated on the jacket structure. 4. Analysis & Results Table 2 presents the salient structural and production details of the three platforms considered in the analytical study for relocation. All the three structures have been analysed with intact number of conductors currently present on the structure. No clamp-on wells have been considered at the re-location sites. All the platforms have been re analyzed with environmental data for new locations. The representative geotechnical conditions of the new fields have been considered in the study. However, the analysis results may be required to be updated depending upon the actual soil parameters at the final released location in the new field. The analysis results discussed in this paper are restricted to evaluation of jacket structural members and piles only. The global structural integrity assessment results for the jacket and pile structure of the three structures along with the proposed plinth (subsea) structure and strengthening measures, as and if required, have been discussed. Depending on the water depth, relocation of the three platforms has been considered as presented at Table 1. The final relocation combinations considered are Platform ‘A’ to location ‘Y’, Platform ‘B’ to location ‘ X ’ and Platform ‘C’ to location ‘ Z ’ ; for which the results are presented in the following section.