New Experimental Equipment for Hydrate Dissociation Studies
Authors: Sinquin Anne , Beunat Virginie 
Published: October 2008

A new experimental set up dedicated to the hydrate dissociation studies is presented. In this new equipment, hydrate dissociation can be achieved by depressurization and/or heating and/or thermodynamic inhibitor injection methods. After a description of the equipment, its capabilities are illustrated by tests with a water + condensate + dispersant additive system. The hydrate formation has been performed in static conditions and closed system. The hydrate formation in the cell is well detected; hydrates form first near the condensate/concentrated emulsion interface. The hydrate was formed essentially with gas dissolved in the condensate phase. Examples of dissociations by depressurization of the cell are presented. The temperature and pressure at different locations of the cell are recorded. The hydrate phase dissociation is clearly highlighted at different points and its impact on the liquid condensate + water and gas phase environment is also seen. The gas and liquids released from the cell are recorded versus time.

This experimental set up is a very good tool to form hydrate or hydrate plug in realistic conditions. Here for example tests represent a shut-in in hydrate stability zone. The system offers the possibility of studying both the hydrate formation and all the methods of hydrate dissociation.

Introduction

As offshore production is going on in deeper and deeper water depth, the pressure and temperature in the production facilities are entering deeper and deeper the hydrate stability zone. In these conditions hydrate formation is feared because it will quickly lead to a plug formation and a production shutin. The deferred or loss of production and the possible high cost of a mitigation rig to melt the plug will induce a significant loss of revenue. Regarding these potential problems, hydrate inhibition and control are key issues of new offshore deepwater field development in which hydrate plug formation must be totally avoided (1).

When looking at the literature, there is little information on hydrate plug problems and remediation (2, 3). On the other hand, it must be pointed out that experimental researches performed on the hydrate plug dissociation are also limited. Statoil (4) and the NTH (5) worked on gas hydrate plug formation and dissociation during the nineties. More recent works have been performed either in CSM (with ice plug converted into hydrate) (6) or at the Saint Etienne School of Mine on ethane hydrate plug (7).

Recently, several articles dealing with hydrate plug dissociation modeling have been published (8-11) and a great effort to improve the models has been made. Hydrate plug dissociation data is and will be needed to test these models and move towards a more accurate and realistic prediction of plug dissociation time.

Experimental set up

Description

The experimental set up is a 2" internal diameter line of 80 cm length cell. The cell is placed in a temperature controlled chamber (Figure 1). The controlled chamber works in the range of 0 to 60°C. The maximum working pressure of the cell is 150 bars. This cell can accept all non corrosive fluids: water, condensate, crude and solid particles.