Prevention of Hydrates in Pipelines using Hybrid thermodynamic Inhibitors.
Abstract
Chemical method is the most efficient and flexible method of hydrate control in offshore operations. In recent times, polymers and surfactants have been used to influence the kinetics of hydrate growth and coagulation.
However, the traditional polar solvents are still relevant because of their ability to melt hydrates.
Due to the large volume of polar thermodynamic inhibitors usually required in the field, this work examines the effect of hybrid hydrate inhibitors (HHI) comprising both polar and ionic thermodynamic hydrate inhibitors.
In this study, a Microsoft Excel-based program was developed for evaluating the effectiveness of various polar thermodynamic hydrate inhibitors and hybrid thermodynamic hydrate inhibitors in preventing hydrate deposition.
Katz plot was used in obtaining the hydrate formation temperature, when the fluid composition and operating pressure were supplied.
Østergaard, Hammerschdmidt and Nielsen Bucklin equation gave the temperature depression and quantity of inhibitor required to prevent hydrate depression in the pipes.
Two pipes, Branch 4 & Branch 9, in a fictitious offshore field were used as case study.
It was discovered that the quantity of Methanol (MeOH) required in Branch 4 and Branch 9 decreased by 44.5% when Methanol-hybrid Thermodynamic Hydrate Inhibitor (consisting of methanol and salt) was used.
The required Mono Ethylene Glycol (MEG) and Di Ethylene Glycol (DEG) also decreased by 33.6% and 35.9% respectively when combined with salt.
It was concluded that the most effective hybrid inhibitor is Methanol-Sodium Chloride hybrid because it saved 44.5% of Methanol when used in Branch 4 and 45% Methanol when used in Branch 9.
Table Of Contents
SIGNATURE PAGE……..i
TITLE PAGE…………..ii
ABSTRACT……………..iii
DEDICATION………….iv
ACKNOWLEDGEMENT….. v
TABLE OF CONTENTS…..vi
LIST OF FIGURES……….vii
LIST OF TABLES………… x
CHAPTER ONE INTRODUCTION
- General……………… 1
- Flow Assurance……………. 1
- Gas Hydrates………………. 2
- Methods of Managing Gas Hydrate Formation in pipes……… 10
- Statement of Problem…….. 18
- Objectives……………………19
- Scope of work…………… 19
CHAPTER TWO LITERATURE REVIEW
- Hydrate Inhibition; Past, Present and Future…..20
- Point of Departure………….. 22
CHAPTER THREE METHODOLOGY
- Hydrate Prediction……………..24
- Temperature depression………..25
- Estimation of Hydrate inhibitor needed in the flow line……. 26
- Spread sheet development……..27
- Case Study…………… 27
CHAPTER FOUR RESULTS AND DISCUSSION
- Results………31
- Discussion……..52
CHAPTER FIVE CONCLUSION AND RECOMMENDATION
- Conclusion……….
- 59
- Recommendation…. 59
REFERENCES…… 60
Introduction
Background Of Study
As the potential for onshore oil and gas discoveries diminishes, oil operators and governments are moving offshore. Many countries with shorelines have already granted exploratory permits, and a large number of these have drilling and production concessions.
The first offshore oil in the world was produced in the late 1940’s. By 1973, production data show that 18.9% of the world’s oil supply was produced from offshore.
It has been said that while onshore reserves will ultimately double, offshore reserves will increase by a factor of four (ETA Offshore Seminars, 1976).
The Nigerian economy is highly dependent on petroleum. Currently, Nigeria has produced oil for over 50 years but the impact of our rapidly expanding demand for crude oil will require exploration of more petroleum prospects.
Therefore, there has been an increasing interest in offshore production in Nigeria in the past few years. Some offshore fields in Nigeria include:
Bonga, Akpo, Erha Field, Agbami, Abana, Amenam-kpono oil and gas field, Ekpe phase II, Exxon East area NGL II, Usan field and Yoho oil field.
Due to extreme water depths and harsh marine environment (extremely high pressures in the cold and dark recesses of the ocean bottom), production in deep water presents challenges far beyond those experienced in shallow waters or onshore.
References
Azarinezhad R., Chapoy A., Anderson R., and Tohidi B. (2010): “A Wet Cold-Flow Technology for Tackling Offshore Flow-Assurance Problems”, SPE 132349.
Becke P., Kessel D. & Rahimian I. (1992): “The influence of liquid hydrocarbon on gas hydrate equilibrium”, SPE 25032.
Campbell Tip of the Month: http://www.jmcampbell.com/june-2010.php
Dana Budd, Danica Hurd, Marek Pakulski, Thane D. Schaffer (2004): “Enhanced Hydrate Inhibition in Alberta Gas Field”, SPE 90422.
Dorrian Helen, , Flow Assurance (2010): “Implement Flow Assurance Strategies to reduce deposit Build up, Maintain Pipeline Integrity and Optimise Flow Efficiency” Flow assurance conference, Aberdeen.
Edmonds B., Moorwood R.A.S. & Szczepanski R. (2001): “Controlling remediation of hydrates in Deepwater Drilling Operations”, Ultra deep engineering supplement to Offshore Magazine, pp 7- 10.