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This paper presents a numerical and analytical study of pipein-pipe installation in deepwater by the J-lay and Steep S-lay methods. In particular it examines the amount and location on plasticity that may be allowed to occur during the installation phase of construction. The influence of the residual strain to operational performance of the line is discussed. The information in the paper provides guidelines for the installation of pipe-in-pipe systems in deepwater as well as indications of the critical areas that require detailed investigation.A general limit of 1% strain during installation has industry acceptance although few projects have put this to the test. The results presented in the paper show this to be acceptable under certain circumstances and perhaps not so conservative in others. It also highlights the importance of understanding the numerical modeling techniques as well as the influence of assumptions in the loading and materials modeling.

Offshore umbilical systems are essential for transmitting power and signals required to operate subsea facilities. In particular, umbilicals are made of a large number of elements with different engineering materials to accommodate constantly increasing requirements from oil and gas industry for production in deep waters and subsea processing. Often offshore umbilicals are installed using a reel lay or a carousel method and hence they are subject to large bending, axial and crush loadings during the installation process.In order to guarantee the structural integrity and installability of umbilicals during the installation process, umbilical manufacturers have to carry out a detailed structural analysis of the umbilicals. Such an analysis requires a deeper understanding in the structural mechanics of complicated cross sections subjected to various loadings. This increases the cost and manufacturing time of the umbilicals. This paper will present a simple method to carry out a detailed three dimensional finite element analysis of the umbilicals which will help to define safe installation limits such as the minimum reel/carousel/sheave(s) radiuses, maximum installation tension and tensioner crush operating loads.A 3 Dimensional Umbilical Simulation Tool, known as 3DUST has originally been developed by DeepSea (Dixon and Zhao, 2008), now a McDermott subsidiary. 3DUST is capable of three dimensional modelling of umbilicals and consists of pre-processing and post-processing features. Using the preprocessing feature, a modelling input deck with different materials, geometries, boundary conditions of any umbilical can be generated. This input deck is compatible with Abaqus finite element analysis software. Once the input deck is analysed, the post-processing feature can generate results with the installation capacity such as bending, axial load, crush load and ovality of the umbilical analysed, which can in turn be used to determine the adequacy of the reel lay or carousel system of the installation vessel.The paper will demonstrate the use of 3DUST for the installability analysis of an example umbilical with original analysis carried out for providing solution to an installation challenge of the umbilical. The paper will also present the results of the example umbilical obtained from 3DUST.A particular significance of the paper is not to demonstrate the computational mechanics involved in the analysis of umbilicals, but to address key challenges in the structural mechanics of the umbilicals and to simplify the umbilicals' analysis method by using 3DUST, a knowledge based system with capabilities including suitable finite element meshing of geometries, material assignments, defining boundary con-ditions and presenting relevant results. It is noted that this method has been applied to many deepwater umbilicals in West Africa, Golf of Mexico and Brazil.

The ultra-deepwater fields in the Gulf of Mexico are among the largest producers discovered to date. However, the reservoirs are interbedded with highly depleted zones, with pressure differentials up to 11,000 psi. The development, testing, and application of wellbore stability modeling software that accurately characterizes fractures, determines the optimal lost circulation material (LCM) blend, and delivers reliable wellbore strengthening results in the problematic production zones are discussed. Wellbore strengthening literature focuses on three fundamental areas: stress caging, fracture–closure stress, and resistance to fracture propagation. Aspects of these approaches were incorporated into a new modeling solution that was calibrated using historical data from nine offset wells. The modeled fracture width predictions were used to design lost circulation material (LCM) treatments with specific particle size distribution values. Each formulation underwent particle-plugging testing in the laboratory, followed by flow loop testing of the best performers for compatibility with downhole tools. The highly interactive process, which currently continues, resulted in successful field applications in similarly complex wells. The new model allowed drilling personnel to identify the parameters most likely to induce fractures. Equivalent circulating density (ECD) had the most impact, followed by minimum horizontal stress, Young’s modulus, fracture length, and Poisson’s ratio. Using modeling outputs, LCM blends were engineered to plug fracture widths ranging from 1,500 to 2,000 microns, significantly wider than previous estimates. Field results indicated that an "extended" ECD margin could be obtained for severely depleted formations. The optimized LCM treatments were applied on two wells with narrow pore pressure/fracture gradient margins and on one well with a severely depleted reservoir (4,600 psi). All three were drilled with zero losses. On a fourth well, the modeled treatment was applied to the leak-off test at the 16-in casing shoe above the production zone. The operator expected a 0.4 to 0.5 lbm/gal increase at best; the actual increase was more than 1.0 lbm/gal. After this interval was drilled, a 14 in liner was set and cemented with zero losses. Such an increase had not been possible on offsets previously. Based on these successes under similar conditions, the operator is currently implementing the model to design wells with extreme depletion to be drilled during 2020. Decades of deepwater experience have yielded numerous best practices for drilling in narrow margins and depleted zones. However, many wells still cannot be drilled without an assurance of effective wellbore strengthening. By removing the limitations of other wellbore strengthening approaches, the field-proven geomechanics modeling software presented in this paper creates a new standard for lost circulation prevention in depleted sands with 8,000 to 11,000 psi differentials.