RasGas is an operator in Qatar's North Field, the world's largest non-associated natural gas field. Field development is ongoing to produce gas primarily for use as feedstock for a number of LNG and GTL plants. Due to the long lead time required for the design and the construction of these plants, it is necessary to establish the feedstock specifications as early as possible. Plant cost is influenced by the non-hydrocarbon gas content (NHCG), particularly H2S and CO2.
After a thorough study of available options for making timely and reliable measurements of H2S and CO2 content of reservoir fluids, it was decided to evaluate Wireline Formation Testers (WFT), both open-hole (OH-WFT) and cased-hole tools (CH-WFT), to acquire samples which could be analyzed for their non-hydrocarbon gas content.
The objective of this program was to obtain and analyze samples that yielded:
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Non-hydrocarbon gas composition comparable with surface recombined DST samples.
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Representative uncontaminated formation fluid (gas), captured and maintained above dew point, suitable for detailed compositional analysis and PVT fluid characterization.
To conduct open-hole sampling operations safely and effectively several challenges needed to be overcome. Three interrelated issues needed to be addressed in order to have a successful operation:
Well control issues
Differential sticking risk
Formation sampling tool performance
This paper addresses the novel solutions RasGas employed to ensure the sampling operations could be performed safely and effectively. Sampling operations have now been conducted in several wells and have met the program objectives with no safety incidents (Nobody Got Hurt).The most recent open-hole wireline formation sampling program yielded high quality fluid characterization information and non-hydrocarbon gas compositions, realizing millions of dollars in savings and taking less time than a conventional DST program.
