Design and Selection of Pipeline Systems to Address the Challenges of Deepwater HPHT Developments

摘要

The selection of the optimum configuration for production pipelines for an HPHT deepwater development presents the system designer with a number of challenges. Typically, there is a requirement to keep the wellhead fluids hot within a highly insulated system to prevent hydrate formation and wax dropout. Insulation systems can comprise either an external (wet) insulation pipe coating or a (dry) pipe-in-pipe (PIP) insulation system. The selection of the preferred system for a development needs to holistically consider their diversity in terms of thermal performance, structural behaviour, installation, integrity management and cost. A particular design challenge for deepwater pipeline systems is to control lateral buckling and mitigate pipeline walking which can arise under extreme HPHT conditions. Generally, as internal pressure, temperature and fluid corrosivity increase, the more challenging and costly the buckling/walking mitigation schemes become. Detailed assessment of buckling and walking has shown significant differentiation in the structural response of wet insulation and PIP systems to the extreme loads, and therefore in the mitigation measures which must be employed. This paper presents how the complexity of different system design strategies for managing pressure and temperature loading can be effectively and robustly managed within a field development project. The paper compares the performance and technical limits of pipe-in-pipe with wet insulated pipelines. The benefits of potential mitigation measures such as subsea HIPPS and subsea cooling spools are also discussed. Introduction As the demand for hydrocarbon continues unabated, the industry seeks to develop reservoirs of ever increasing pressure and temperature in ever increasing water depths. Exploitation of these deepwater high pressure, high temperature (HPHT) reservoirs presents a number of technical challenges to the industry, one of which is the design of the pipelines systems. The generally accepted envelope of HPHT classification[1] is reservoir formation pressures in excess of 10,000 psi (690 bar) and reservoir temperatures in excess of 300 °F (149 °C). The pressures and temperatures at the subsea wellhead and subsea facilities will generally be somewhat less than reservoir conditions due to pressure head and thermal losses in the wellbore. Furthermore, subsea pipelines will behave in a high temperature manner at somewhat lower temperatures (e.g. significant material strength derating, severe Euler buckling response etc.) and hence the HT temperature limit is taken as 250°F (121 °C), Figure 1. Figure 1 also includes two further classifications of Extreme HP/HT for pressures and temperatures in excess of 15,000 psi (1,034 bar) and 350 °F (177 °C), and Ultra-HPHT for pressures and temperatures in excess of 20,000 psi (1,379 bar) and 400 °F (204 °C).