Flow Assurance for Deep Ocean Mining - Pressure Requirement Through S-Shape Riser and Jumper
Authors: Parenteau Thomas , Lemaire Antoine 
Published: May 2011

The flow assurance aspects of all subsea projects have a major contribution to the pipe design, field layout, choice of lifting equipment (subsea-pump or air lift), power requirement and system operability. In the context of deepwater mining, the main task is to estimate the pressure drop in the jumper and riser as well as the liquid-solid or gas-liquid-solid flow regime directly impacting the erosion rate and risk of pipe clogging. These are needed to guarantee the production target at steady state and to guarantee the system operability in transient mode at shut-down and system start-up cycles. Current knowledge of solid transport has successfully characterized pneumatic and hydraulic transport of fine particles (powders, sand, or small gravel) in large diameter pipelines. Semi-empirical theories based on concepts such as isolated or hindered slip velocities, mixture properties, and in-situ concentration have emerged to analytically resolve the flow behavior in vertical, horizontal, and inclined pipe. The context of deepwater mining pushes these theories beyond the existing application cases due to the significantly larger particle size combined with small diameter riser and jumper including wave shape to accommodate vessel motions and excursion requirements.

The current papers summarize the the flow tests made in a subsea mining experimental flow loop including horizontal and S-shape sections. These tests allows to identify the main flow characteristics of the slurry in subsea mining condition transporting large particles (5mm to 20 mm) in reduced diameter flexible pipe (4??).

INTRODUCTION

As described in P. Espinasse paper [1], Technip is supporting an internal R&D program that should allow the understanding of critical parameters essential to the design and operability of a subsea mining system. Within this R&D program, a flow assurance study takes place in order to estimate the pressure drop through the riser and jumpers both including an S-shape configuration to respectively accommodate the vessel motion and a large excavation range. An illustration is presented in [T. Parenteau [2] has reviewed the current knowledge for vertical slurry transport to show that the actual available theory based on in-situ concentration is plenty satisfactory to estimate the pressure drop through a straight riser transporting large particle size (2??) in small diameter riser (8?? to 10??). In the same review, T. Parenteau has shown that when introducing an inclined part in the experimental set-up the pressure drop correlations diverge from the prediction due to the formation of significant bed at the bottom of the pipe.

In order to understand the key parameters influencing the pressure drop in the S-Shape riser and jumper Technip has built a small scale flow loop test to visualize the flow and measure pressure drop. The parameters that are studied are the flow regime, variation of concentrations, diameters and densities in both S-Shape and Horizontal sections are studied. Figure 1].

T. Parenteau [2] has reviewed the current knowledge for vertical slurry transport to show that the actual available theory based on in-situ concentration is plenty satisfactory to estimate the pressure drop through a straight riser transporting large particle size (2??) in small diameter riser (8?? to 10??). In the same review, T. Parenteau has shown that when introducing an inclined part in the experimental set-up the pressure drop correlations diverge from the prediction due to the formation of significant bed at the bottom of the pipe.