Transient Modelling and Sensitivity Analysis of Influxes in Backpressure MPD Systems

Abstract

A transient flow model capable of modeling gas solubility will be used to perform a sensitivity analysis of kick behavior in a subsea backpressure MPD system when using oil based mud. The parameters of interest are choke pressures, pit volume, and return rates. At HPHT conditions, gas kicks can be entirely dissolved in oil based mud. However, when being circulated upwards, free gas will emerge at a certain depth. The required choke pressure to maintain a constant bottomhole pressure depends on the amount of gas released from the mud and where this occurs. Another parameter that impacts both choke pressure and return flow is the geometry, whether we have a wide riser for subsea MPD or are considering an MPD operation from a fixed installation with a narrower geometry. In this paper, the riser geometry will be varied. The paper will contribute in showing how transient models can assist in the planning of MPD operations. It will also provide insight into influx behavior and its impact on surface parameters with focus on oil based mud.