Karachaganak, one of the world's largest oil and gas condensate fields, is located north of the Caspian Sea, near Aksai in north-western Kazakhstan. It covers more than 280 square kilometres and holds more than 1.2 billion tons of oil and condensate and 1.35 trillion cubic meters of gas. As the largest internationally funded project in Kazakhstan, development is being overseen by the Karachaganak Petroleum Operation B.V. (KPO), which includes four international partners: BG Group of the UK, Eni of Italy, Chevron Texaco of the United States and LUKOIL of Russia. KPO has a production sharing agreement with the Kazakhstan government to enhance production.

Unfortunately, the field also presents some of the harshest operating challenges for gas compression and re-injection equipment. Key
among them are a high concentration of hydrogen sulphide (H2S)
in the petroleum and natural gas reservoirs and extreme seasonal temperature ranges between -40°C and +40°C that commonly wreak havoc on mechanical components.

Performance-based agreement
In 2003, GE supplied KPO with three sour gas re-injection units, each consisting of an MS5002D gas turbine and three compressors. Our service division was awarded a comprehensive five-year Contractual Service Agreement (CSA). This global maintenance agreement covers all rotating equipment located at the Karachaganak site:

• 3 turbocompressors for high-pressure re-injection. All these units were completely supplied by GE's Nuovo Pignone of Florence Italy.
• 3 reciprocating compressors for Flash Gas (also supplied by Nuovo Pignone)
• 12 compressors (reciprocating and centrifugal) for various purposes and provided by different suppliers

It is important to note that the CSA includes the possibility of incentives driven by high availability of the units, injury rate during site activities,
NOx and CO emission rates from gas turbines and the number of trips
due to alarms.

Outstanding performance record
The whole reinjection system has been in operation since 2003 and in the first two years has proven to be very reliable. In fact, despite frigid temperatures in the winter of 2004-05, one of the Unit 2 compressors achieved 100% availability in every month but January. Availability of 99% was consistent across all three Unit 2 compressors for the entire winter.

"The successful sour gas re-injection performed by these machines under such extreme conditions produced results that may be unprecedented in the oil and gas industry," said Claudi Santiago, president of GE's Oil & Gas business.

KPO was fully satisfied with the first maintenance operations carried out on Unit 2 in July 2005.

The MS5002D gas turbine hot gas path inspection was performed after 16,000 equivalent operating hours. Upon inspection, no damage was found in any dismantled part (i.e., combustion chambers, liners, cross-fire connections, transition pieces, nozzles) – only normal wear after 10,000 running hours.

1. Fuel gas nozzle 2. Liner

The third stage (high pressure) compressor BCL304d was dismantled to check the rotor which had shown signs of small vibration – subsequently determined to be caused by a 130 g piece of strainer found in the suction of the first-stage impeller. After removing the obstacle, an internal inspection of the channels was carried out with a boroscope to confirm
the impeller integrity. Inspection of the whole rotor showed no traces of corrosion or mechanical stress.

This is even more significant if one takes into account that the compressor was subjected to all of the stresses of commissioning activities – during which the plant was operated in a semi-manual mode. The inspection also proved that the gas processing meets all quality specifications.

A key to the success of these compressors was effective collaboration between the KPO and GE maintenance teams. This collaboration was greatly enhanced by a preventive maintenance CSA, featuring continuous plant and machine data monitoring. Remote monitoring and diagnostic activities guarantee daily monitoring of all parameters. By gathering and analyzing these huge volumes of data, GE reliability and availability experts can help prevent dangerous situations and help our customers to operate their plant more safely.

Designed for safety and reliability
Unit 2 processes hydrocarbons from field wells and produces condensate and gas streams. The gas is used as fuel for the Karachaganak power plant that generates electricity for field facilities. Fuel gas for the three gas turbines is used to drive the re-injection compressor at Unit 2 and transport it via pipeline to Orenburg. The remaining gas is re-injected to maintain reservoir pressures. Condensate then passes from Unit 2 for further treatment before being transported via pipeline to market.

Frame 5 gas turbine		The associated gas is contaminated by 7.7% hydrogen sulphide (H2S) which has to be separated from the products including the fuel gas used on site. It is not separated from gas which is re-injected into the reservoir to maintain the pressure and enhance recovery of heavier hydrocarbons.

This very toxic component requires exceptional safety measures to be adopted not only on the compressor train but across the plant with special emphasis on the high-pressure section.

A major risk during winter is the formation of liquid condensation in pipes filled with sour gas under pressure, but not normally in use (e.g., as
by-passes, anti-surge lines, etc.). This condensation could cause premature corrosion in the pipes – so the layout of the whole piping system has been designed with heating systems at critical points.

In addition to toxic gas leaks, exhaust emissions are also of great concern. To reduce emissions, the turbines are equipped with a DLN system that ensures low NOx and CO values. Exhaust is continuously monitored and remotely tuned to operating specifications via a real-time internet interface with our Florence headquarters.

Because of safety concerns about the high toxicity of the gas being handled, a detailed risk assessment was performed to identify any possible incidents and their potential outcomes, such as fire, toxic release or over-pressure situations.

Centrifugal compressors

As a consequence of this study, both the compressor design and the
turbo compression train layouts differ from similar systems used for
re-injecting sweet gases with no H2S. The very high-density centrifugal compressors used for the Karachaganak project are designed with special emphasis on rotor dynamics and gas sealing. Extremely rigid shafts are used to minimize shaft vibration at all operating conditions, including close-to-surge operations. Gas sealing for both casings and shafts are designed to maximize redundancy and achieve the greatest possible safety conditions for all potential situations.

From a layout point of view, the main results of the risk assessment study included:

• Special heat and ventilation of the compressor building
• Toxic gas dispersion analysis
• Detailed location of gas sensors both inside and outside of the building
• Positioning of the local control room for each compressor train
• Safety escape route design

Safety concerns were also the driving force behind KPO's decision to select GE as its sole service provider for maintenance services on all 18 compression trains on the injection island.

Based on its success to date, GE is planning further improvements in the Karachaganak field operations. "We are working to maximize gas injection, decrease unscheduled shutdowns and fully exploit the availability of the machines to increase production and keep flaring as low as possible," said Santiago.

Additional remote services (similar to the current monitoring, diagnostics and tuning capabilities) are being introduced to further prevent equipment failures and reduce maintenance downtime. These will help customers reach further frontiers in oil and gas field development.

For more information, please contact:
Alberto Tesei
alberto.tesei@ge.com