OUR GREAT MINDS

by Shane Crawley

Flair & Isotope Logging: Brings Early Light to the Reservoir Fluid

Mud-Gas-Logging

“Until recently, standard mud-gas-logging technologies did not offer the resolution and sensitivity necessary to provide quantitative hydrocarbon description. However, recent developments in advanced mud gas extractors and improved analytical detectors have increased reliability and accuracy of mud-gas fingerprinting. Thus, during the drilling of a given well, mud- gas fluid fingerprints can be correlated within a given well and mapped to subsurface structural features, such as faults and seals or different hydrocarbon bearing intervals. By providing this during the drilling process, anomalies observed in these fluid facies logs can be investigated in more detail during formation evaluation.” SPE 109861 (SHELL)

Drilling Challenges

Drilling challenges and their associated costs are two factors that have led to the development evaluation techniques, they provide a robust picture of the reservoir and fluids therein. Determining the nature and properties of formation fluids is critical in successful appraisal and development of any oil or gas field. Traditionally, the nature and properties of formation fluids were not available during the drilling process.

Fluid Logging with FLAIR provides information for fluid characterization that is complementary to standard down hole fluid analysis, the advantage being that it is available quickly while drilling the well, prior to any other formation evaluation tools being run down hole.

Analysis of Data

Analysis of such data allows the interpreter to fingerprint the penetrated hydrocarbon accumulations and begin mapping fluid facies1 while drilling. This very early assessment allows for faster decisions in an ever-more costly environment. Hydrocarbons are continuously extracted under high temperature and controlled-extraction conditions from the drilling mud at surface, and transported to a specially designed detector, which is a combination of gas chromatograph and mass spectrometer.

The combination of constant thermodynamic extraction, advanced detector, calibrated extraction efficiency for various mud types, and recycling correction provides necessary conditions to achieve quantitative C1–C5 (methane to pentane) composition, and qualitative information on the C6–C8 (hexane to octane) components. These factors also enable repeatable conditions for multi-well correlation within an oil field. Mapping of fluid facies provides early assessment on reservoir connectivity, presence of barriers, compartments, fluid contacts and gradation. In certain cases, FLAIR has provided early information and identified bypassed pay zones before any formation sampling tools are run down hole.

Geoservices Isotope Logging

Geoservices Isotope Logging is performed simultaneously to FLAIR and on a continuous basis by measuring the variation in a stable isotope of methane (δ13C-CH4). This information allows a fast and integrated interpretation of the geological and geochemical system, utilizing all available data. The integration of this data with FLAIR and the various other formation evaluation techniques provide a significant and more accurate picture of the formation fluid distribution and characterization.

Flair and Isotope Logging services

FLAIR and Isotope Logging services have been successfully used worldwide in exploration, appraisal, and development wells in all geological settings and complex operational conditions. When cross- referenced with multiple fluid analysis techniques validity of their data collected is enhanced and provides an internal quality-check amongst each other. Today FLAIR and Isotope Logging technologies offer the resolution and sensitivity necessary to provide quantitative hydrocarbon description with their main advantage being that data is continuously and quickly derived in a non-evasive manner.

Benefits & Applications

FLAIR and Isotope Logging technologies provide the following benefits and applications:

  • Early fluid facies characterization and formation fluid compositional analysis guide critical operational decisions, which can provide significant economic savings. This includes optimization of down hole fluid sampling program to obtain best representative samples.
  • In exploration wells, it provides an early assessment of the composition of potential pay zones while drilling. Due to a high degree of drilling uncertainties in such wells, FLAIR can sometimes be the only available information regarding down hole fluid.
  • Being a surface measurement, it can also be used for logging fluids in high-pressure, high-temperature (HPHT) environments, where conventional tools cannot be used.
  • In deepwater settings with low mud temperature on surface, FLAIR helps characterize the formation fluid with a reliable quantitative compositional analysis.
  • Continuous isotope logging provides a dramatically improved depth resolution, allowing the identification of small-scale features that would be missed by collecting spot samples for a consequent isotope analysis.
  • Isotope data provide information about encountered fluids, their origins, characteristics and behavior in the subsurface.

For more details of this story, refer to the following SPE publications, SPE-84383, SPE-109861, SPE-109684.
1 Fluid Facies: A geological interval where formation fluid exhibits homogeneous composition

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