document

Abstract

South-Pars Phases 2&3 development in Iran is a "wet scheme" base design: no process is performed offshore, all the produced fluids (sour gas + condensate + water) are directly sent to shore through two 32" 109 km long sea lines. Corrosion and hydrate protection is based on buffered glycol (MEG+MDEA) which is regenerated onshore and sent back to the platforms through two 4 1/2" piggyback lines.

The concomitant injection of a Kinetic Hydrate Inhibitor (KHI) and a Corrosion Inhibitor (CI) was initially considered as a back-up solution. This paper presents the field experience with KHI and CI injection which had to be applied for the field start-up during respectively 125 days and 80 days for each sea line.

This case represents the first large field application of KHI in the Middle-East and the potential of such Low Dose Hydrate Inhibitor (LDHI) is underlined.

Introduction

The conventional chemical treatments for the prevention of hydrate formation in wet gas applications include methanol and glycol (mono ethylene glycol - MEG) for thermodynamic inhibition and tri ethylene glycol for gas dehydration. It is however recognised, when only hydrate prevention is considered, that the cost of such technique can be prohibitively expensive for new developments. Replacement of the traditional thermodynamic inhibitors is highly desirable from both commercial and Health & Safety considerations. This seems achievable by using alternative Low Dose Hydrate Inhibitors (LDHI) whose interest is undoubtedly growing within the oil and gas production industry. These inhibitors can be divided into two groups, kinetic hydrate inhibitors (KHI) and anti-agglomerate (AA) agents.

Kinetic Hydrate Inhibitors have been field trialled with limited success, due to operational conditions, in the USA, Canada, the Middle East and Europe. More successfully KHIs have been applied in the UK sector of the North Sea, Refs- 1-4.

Although anti agglomerate chemistry is not yet as commercially developed as kinetic inhibition, there are a growing number of AA applications in the Gulf of Mexico (USA) and the North Sea (UK and Dutch sectors) and the chemistry is showing great potential in deep water developments, Ref- 5. However there remain some concerns about the ecotox rating, as determined using the ecotox test regime used to assess the impact of chemicals in all sectors of the North Sea.

Regarding TOTAL Group experience with LDHI, some field tests with both KHI and AA had been performed in France in 1997, Ref-6, and in Argentina in 1999.

When sour gas is considered, corrosion concerns are strengthened. One solution to prevent both corrosion and hydrate problems in wet gas applications is the pH stabilisation: buffered MEG is continuously injected offshore and remains at pH>7 throughout the sea line, Ref- 7-8. This solution presents the advantage to avoid any gas/liquid separation offshore, i.e. minimise the installations on the platforms. This is the basis design solution retained against hydrate and corrosion for the South Pars Phases 2 & 3 project.

The South Pars Phases 2 & 3 development scheme is based on the multiphase production and transport of all fluids from the wells (liquid hydrocarbons, gas and water). At time of writing, this field represents one of the longest multiphase developments in the world.

Field overview

TOTAL SOUTH PARS is developing the SOUTH PARS Phase 2 & 3 Project for National Iranian Oil Company (NIOC) in Iran. This project includes offshore facilities (wells, platform and undersea pipelines) and onshore facilities for the processing of the reservoir fluid.

The Phase 2 & 3 complex is located on the Iranian coast of the Persian Gulf near ASSALUYEH village (approximately 270 km South East of Bandar Busher).

The total capacity of the Phase 2 & 3 onshore facilities is 2,000 MMSCFD of reservoir fluid. They include all processing units, utilities, off sites and infrastructure necessary to produce sales gas and stabilised condensate from the reservoir fluid delivered to the onshore plant via two multiphase sea lines.