Analyses of a Large Diameter Steel Lazy Wave Riser for Ultra Deepwater in Campos Basin

Abstract

Petrobras is going deeper and some fields are feasible only if the production platforms are installed in ultra deep waters, close to the wells. In one case in Campos Basin, for example, the platform will be installed at 1255 m water depth and the solution to allow the production is based on the evolution of flexible lines for high pressure and high loads. For the oil export line, however, a steel rigid line was chosen, due to the large diameter. Some analyses were performed in order to make it feasible the installation of an 18-inch SCR export oil line. Due to fatigue loads, the free hanging catenary configuration did not match with API RP 2RD recommendations, so Petrobras decided to change the original shape to Lazy Wave in order to reduce the top loads and increase the fatigue life. But, some configurations are not feasible to install. High angles close to the installation vessel or high stresses close to the flotation segments are some problems that must be solved. This article will present the steps made to reach a configuration that will make feasible the installation of this riser, in parallel to the static and dynamic analysis, to maintain the stresses in an allowable level, in accordance with API RP 2RD.

Vessel relocation solution for steel catenary riser touch down fatigue management

“…The objective functions' values at the feasible design points can be obtained by evaluating them at 𝐗 𝐅𝐃𝐒 as shown in equation ( 20). The corresponding feasible set of index system, 𝐈 𝐅𝐃𝐒 , which is a subset of 𝐈 is expressed as shown in equation (21).…”

“…Several efforts have been committed by research institutions and the offshore industries to increase the application of SCRs for deepwater hydrocarbon extraction [11][12][13]. These solutions include the SCR configuration change such as steel lazy wave and shaped riser solutions [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32], the alternative material application for SCR design such as high strength material including titanium for the riser pipe joint [2,11,[33][34][35], the advancement in riser soil interaction modelling such as the development of non-linear riser soil interaction models [36][37][38], the decoupling of SCR from vessel motion such as the uncoupled steel catenary riser systems [39][40][41][42], the vessel relocation to effect fatigue damage spreading along the SCR TDZ [12,[43][44][45], the use of upset pipe end and titanium welding connection to improve the life of the riser at welded joints [11,35,[43][44]…”

Centrifuge modelling of whole-life pipe–soil interaction in clay with different overconsolidation ratios

“…Offshore production risers, including steel lazy wave risers (SLWRs) and steel catenary risers (SCRs), are pipelines transporting oil and gas from the subsea fields to the production vessels (DNVGL, 2017a(DNVGL, , 2017b. SLWRs have been used recently as an alternative to SCRs, with the benefits of reduced daily motion amplitude (where fatigue damage mostly occurs) and improved performance under extreme storm motion at the pipe-soil contact area (Franciss & Ribeiro, 2004;Eyssautier et al, 2018). The contact area, also known as the touchdown zone (TDZ), is the location of complex soil-structure-fluid interaction, which influences the evolution of pipe-soil stiffness (Willis & West, 2001;Bridge et al, 2003;Sharma & Aubeny 2011;Clukey et al, 2011).…”

Vessel relocation strategy for multiple steel catenary riser fatigue damage mitigation

“…These solutions include the SCR configuration change, alternative riser pipe material application, increased understanding of riser soil interactions, decoupled SCRs, upset pipe end, hydrodynamic dampers, vessel relocation, etc. SCR configuration can be changed to obtain steel lazy wave risers (SLWR) and shaped risers [10][11][12][13][14][15]. This will require the installation of buoyancy modules on the section of the SCR.…”