[Gas hydrate continuous inhibition and ways to reduce the cost of field development projects]

By

ACKNOWLEDGEMENT

I would take this opportunity to thank my research supervisor, family and friends for their support and guidance without which this research would not have been possible.

DECLARATION

I, [type your full first names and surname here], declare that the contents of this dissertation/thesis represent my own unaided work, and that the dissertation/thesis has not previously been submitted for academic examination towards any qualification. Furthermore, it represents my own opinions and not necessarily those of the University.

Signed __________________ Date _________________

ABSTRACT

A high-pressure test wheel for flow simulation has been used for the specific purpose of studying gas hydrate formation and inhibition in hydrocarbon gas-water-oil systems. The stainless steel wheel, which could be rotated in a temperature controlled chamber at a constant angular velocity, was equipped with pressure (0-150 bar), temperature (-10-150 °C) and torque sensors. The sensor signals were transferred to a real time PC-based data acquisition system. A video camera mounted on a Perspex window on the wheel allowed recorded data to be correlated with the visual information obtained Viscosity changes, hydrate initiation and agglomeration changes in hydrate macrostructure and deposits on the pipe wall were easily detected. The gas hydrate inhibiting properties of several chemical additives have been examined. The discouraging results obtained with some previously patented additives indicate that the rotating wheel represents a more conservative and realistic test method than those hitherto applied.

TABLE OF CONTENTS

ACKNOWLEDGEMENT2

DECLARATION3

ABSTRACT4

CHAPTER 1: INTRODUCTION6

CHAPTER 2: EXPERIMENTAL SET-UP8

Experimental Work9

Chemical Additives9

CHAPTER 3: RESULTS11

Changes in fluid flow properties during conversion of free water to hydrates12

Ways Reducing the cost of the development field Projects18

CHAPTER 4: DISCUSSION24

Kinetic inhibition of hydrate formation25

Summary of the effect of additives25

CHAPTER 5: CONCLUSIONS27

REFERENCES28

CHAPTER 1: INTRODUCTION

The development of offshore mature basins such as the North Sea is increasingly characterized by marginal reservoirs. Feasible economic development of these reservoirs requires a shift towards total subsea production systems without fixed or floating production platforms (Basniev & Nifantov, 2005). Unprocessed or minimum processed reservoir fluids will be transported to a central processing facility or ultimately to shore. One of the key issues of total subsea production systems is multi- phase flow technology with particular emphasis on gas hydrate control technology. Gas hydrates are crystalline compounds composed of water and gas (Sloan, 1990). The pressure-temperature conditions in subsea pipelines favors the formation of these hydrates. If extensive formation takes place, it may result in clogging of the pipeline due to deposits on the pipe wall or by formation of plugs in bends, valves, etc. (Basniev & Nifantov, 2004: 33).

Subsea transportation of unprocessed or minimum processed well fluids over long distances today re- quires the use of large amounts of methanol or glycols for hydrate inhibition. The effect of these additives is to decrease the water activity to an extent that markedly reduces its ability to participate in hydrate formation, and thereby in a lowering of the hydrate formation temperature. The amount of inhibitor necessary to obtain the desired lowering of the hydrate formation temperature is substantial, usually ...