Abstract
Flow restart after a planned or emergency production shut-down of waxy oil offshore pipelines is a concern to operators. Since reliable methods to predict the required time and input pressure are not available, there is a high risk to lose a transportation or production flow line. So far most of predictive models have been based upon the assumption that gelled crude behaves as an incompressible high viscous fluid. Field cases and laboratory model pipeline tests have shown however that these calculations give systematically overestimated restart pressures, giving the opportunity to lower investment development schemes (such as less insulated pipelines or no extra pumping requirement). Since offshore oil industry is facing more and more challenging production environments, such as deepwater and marginal fields with long tiebacks, this issue is becoming even more stringent, affecting directly the investment cost required for the development of waxy oil resources.
The aim of this work was to investigate the problem of restart of waxy crude oils and preliminarly to present a new mathematical model as a robust pipeline restart predictive tool with a sound physical basis. Although this topic has been investigated for more than forty years, until recently, when Vinay et al (2006, 2007) and Wachs et al (2009) developed a theoretical framework for start-up transients of compressible yield stress fluids, no one had considered the old and simple plastic Bingham Model (BM) (Bingham, 1919). Beyond the model description, a first analysis comparing model forecast with experiments carried out in a model pipeline with multiple pressure taps at constant injection flow rate was carried out.
