CORROSION CHALLENGES FOR THE OIL AND GAS INDUSTRY IN THE STATE OF QATAR

Roy Johnsen

Norwegian University of Science and Technology (NTNU), Richard Birkelands vei 2b, N-7491 Trondheim, Norway

Keywords; Qatar, oil and gas, corrosion, hydrocarbon mixture, aquifer water

Abstract

In Qatar oil and gas has been produced from onshore fields in more than 70 years, while the first offshore field delivered its first crude oil in 1965. Due to the atmospheric conditions in Qatar with periodically high humidity, high chloride content, dust/sand combined with the temperature variations, external corrosion is a big treat to the installations and connecting infrastructure. Internal corrosion in tubing, piping and process systems is also a challenge due to high H2S content in the hydrocarbon mixture and exposure to corrosive aquifer water. To avoid corrosion different type of mitigations like application of coating, chemical treatment and material selection are important elements. This presentation will review the experiences with corrosion challenges for oil & gas installations in Qatar including some examples of corrosion failures that have been seen.

Introduction

The first oil well in the State of Qatar was spudded in October 1938. This was an onshore well – named Dukhan 1 – that produced 5.000 barrels per day in January 1940. The first offshore concessions were granted in 1949. However, due to political reasons the first commercial offshore fields - Idd Al-Shargi and Maydan Mahzam fields - were discovered in 1960. In 1970 the large Bul Hanin field were discovered and came on stream in 1972. In these early years major international oil companies were responsible for the exploration activities in Qatar. However, early 1970-ties, the State of Qatar got its independence from UK and in 1974 they nationalized the oil sector and established Qatar Petroleum (QP). During the coming years Qatar took full control over all oil and gas activities onshore and offshore and the international oil companies were “sent back home” for a period.

In 1991 Qatar intensified their focus on oil and gas exploration and production. This resulted in a boost in oil & gas production from existing and new discovered offshore fields. To assist QP in more efficient exploration and production, international oil companies like ExxonMobil, Occidental, Total, Shell and Maersk Oil were invited to participate in the activities. All these international operating companies have been active during the last years bringing both capital, technology and technical skills to develop and improve the oil and gas exploration and development in the Qatar.

The North Field (together with South Pars on the Iranian continental shelf) - the world’s largest single non-associated gas field - located in the Arabian Golf is shared between Qatar and Iran. The field holds an estimated 1,800 trillion cubic feet (51 trillion m3) of in-situ natural gas and some 50 billion barrels (7.9 billion m3) of natural gas condensates. The field was discovered in 1971 but the first gas was produced in 1991. Still the North Field is the main field for producing natural gas in Qatar.

Due to the easy access to huge amount of natural gas in Qatar and the demand for utilizing this gas commercially, the development of downstream industry to utilize the gas reserves have been a prioritized activity by the Qatar authorities. Big onshore petrochemical plants have been developed in two main regions as can be seen in Table I:

Table I. Overview of main onshore process plants in Qatar.

The daily production volumes in Qatar in 2012 were:

• Gas   150*109 Sm3
• Oil   1.5*106 barrels

Operation conditions in Qatar

Atmospheric conditions

The environmental conditions in Qatar are a strong driver for atmospheric corrosion on metallic materials and degradation of coatings. It occurs when the surface is wetted by moisture formed due to rain, fog or condensation. Atmospheric corrosion is a complex process involving large number of interacting and constantly varying factors such as e.g. weather conditions, air pollutants, actual metal and surface condition. Studies have demonstrated that most atmospheric corrosion phenomena are an electrochemical nature. These corrosion phenomena are influenced by several environmental factors like [1,2]:

• Atmospheric pollution
• Airborne salinity
• Sand/dust
• Temperature
• Time of Wetness

A classification of the corrosivity of an atmosphere is given in ISO 9223 [3]. In this standard the corrosivity is divided into six classes – Category C1; Very low corrosivity, CX: Extreme corrosivity.

Hydrocarbon mixture

The composition of the hydrocarbon mixture varies between different fields and with type of field – oil reservoir or gas/condensate reservoir. One main challenge is the H2S content of the reservoirs that can give partial pressure of H2S in the range up to (and even above) 10 bar. This means that the reservoir fluid (hydrocarbon mixture) is characterized as sour according to ISO 15156 and materials have to be selected and qualified according to ISO 15156 – Part 2 and 3 [4]. Typical reservoir values are given in Table II.

Table II. Typical reservoir data for oil and gas/condensate wells in Qutar.

Aquifer water

In Qatar natural aquifer reservoirs exists in the ground. These sources are used for pressure support to wells (Powered Water Injection – PWI). In addition many production wells go through the aquifer. Since these aquifers are used to dump produced water from oil & gas, they contain a significant amount of dissolved salts in addition to presence of H2S, CO2 and sulfate reducing bacteria (SRB). Typical values are; total dissolved solids up to 50.000 mg/l, chloride content up to 40.000 mg/l, pH ≈ 6.5, water temperature < 40°C, CO2 < 80 mg/l, H2S < 20 mg/l. They can also solved contain oxygen. Due to this composition the aquifer is often a corrosive fluid.

Main material challenges from earlier experiences

The biggest treat to the integrity of oil and gas facilities is corrosion and fatigue. This has been documented by different reports. Statoil presented one analysis based on all material related failure analysis done in-house during the period 1997 – 2010. Figure 2 Left shows a summery of the findings; 62% of all failures were caused by corrosion and fatigue with an equal potion of each failure mechanism. Qatar Petroleum (QP) did a similar evaluation of reported material related failures during the period 2002 – 2006. The output from this evaluation – shown in Figure 2 Right – shows that for 29% of the failures corrosion was the root cause of failure.

These analyses confirm the experiences from other oil & gas operators; Corrosion (and fatigue) is the biggest challenge for the integrity of oil and gas facilities. This is one main driver for ISO developing the standard “Petroleum, petrochemical and natural gas industries - Materials selection and corrosion control for oil and gas production systems” [5]. This document describes preferred materials for the different parts of the oil and gas production chain (not the downstream part, e.g. refinery) and is based on “best practice” from the major oil and gas operators in the world.

Corrosion challenges in Qatar

Corrosion under atmospheric conditions

Due to the special atmospheric conditions in Qatar external corrosion has been a major challenge for the operating companies – both onshore and offshore. For structural parts carbon steel is the main material choice. To prevent external corrosion carbon steel needs to be protected by a coating. The preferred solution is to apply an organic coating (often called a paint) to the structure to be protected. To secure a coating system with acceptable lifetime (min. 10 years maintenance interval), important factor are; selection of coating system, pre-preparation/cleaning before coating, application and curing. ISO 12944 “Paints and varnishes – Corrosion Protection of steel...