Litho Scanner Service in Cased Hole Directly Determines Total Organic Carbon in Unconventional Reservoir

Published: 03/07/2018

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Openhole logging prevented by casing drilling

When a well being drilled in an unconventional resource play in the Yukon encountered problems in the section to TD, casing drilling had to be employed to finish the well. The casing prevented obtaining openhole logs over the well's bottom section or collecting samples of the formation with sidewall coring for laboratory analysis. To evaluate the formation lithology and hydrocarbon potential of the cased section, the operator needed a timely, efficient, and accurate approach that would provide information equivalent to that delivered by openhole logs.

Graph: Litho Scanner Service in Cased Hole Directly Determines Total Organic Carbon in Unconventional Reservoir
The close comparison in the overlapped section of Litho Scanner service’s openhole dry-weight elemental concentrations (OH, magenta) with those independently processed from cased hole measurements (CH, black) validated the offsets that were determined to correct for the effect of the casing and cement.

TOC directly determined in cased hole with spectroscopy logging

Litho Scanner high-definition spectroscopy service employs both inelastic and capture gamma ray spectroscopy to quantify elemental weight fractions. The continuous measurement of formation carbon is coupled with an assessment of inorganic carbon from the mineralogy to compute robust, accurate TOC data that is independent of formation water salinity and does not require core calibration or previous knowledge of the kerogen type or maturity. The elemental concentrations are processed to generate the mineralogy and lithologic fractions. Matrix properties such as grain density and sigma can also be computed to improve the accuracy of the porosity and saturation calculations.

Cased hole accuracy verified by agreement with overlapped openhole section

Logging through casing with Litho Scanner service in the TD section of the well overlapped with a section in the openhole logged interval. To account for the casing and cement in the logging response, offsets were selected using Litho Scanner service's cased hole calibration standards and information from the overlapped openhole section.

Processing then used the offsets to accurately compute a robust lithology, TOC, and sigma for the cased hole environment from the dry-weight elements. Confidence in these values was verified by their excellent agreement with the openhole logs in the overlapped section. With these answers, the operator was able to optimize the completion for the lower cased hole section.

Graph: Litho Scanner Service in Cased Hole Directly Determines Total Organic Carbon in Unconventional Reservoir
Corrected for the effect of casing and cement, Litho Scanner service’s cased hole logs (CH, black) agree well with openhole logs (OH, magenta) from the overlapped section in the well
Canada, North America, Onshore

Challenge: Evaluate formation lithology and hydrocarbon potential of an unconventional reservoir in a section of the well that had to be drilled with casing, which prevented obtaining any openhole logging measurements or sidewall core samples for laboratory analysis.

Solution: Run Litho Scanner high-definition spectroscopy service to measure elemental concentrations as the basis for accurately determining total organic carbon (TOC), lithology, and sigma independently from the formation water salinity or calibration with core analysis.

Results: Conducted a thorough assessment of the cased hole section for optimizing the completion on the basis of accurate, quantified data from Litho Scanner service instead of estimating properties or relying on lower resolution conventional cased hole logs.

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