Schlumberger

Case Study: GeoFlex Service Identifies Subtle Mineralogical Differences in Clay-Rich Legacy Cuttings for Maersk

Cuttings characterization closely matches laboratory testing, proving wellsite capability

Challenge: Identify an advanced surface logging technology for resolving uncertainty in geological formation characterization and improving mineralogical mapping.

Solution: Characterize lithology with laboratory-quality precision using the GeoFlex quantitative cuttings analysis and imaging service at the rig site.

Result:

  • Provided measurements that closely correlated with core sample analysis data.
  • Identified a decrease in illite and muscovite and an increase in kaolinite that were missed by LWD gamma ray and resistivity logs.
  • Detected an increase in quartz that successfully identified the top reservoir sand.

Improve wellsite characterization

Maersk Oil Angola wanted to more accurately identify formation tops and mineralogical changes at the wellsite. In an effort to increase certainty and improve mineralogical characterization, Maersk was actively seeking a more advanced surface logging technique.

Analyze cuttings with laboratory-quality precision

Schlumberger recommended the GeoFlex quantitative cuttings analysis and imaging service, a modular service that provides near-real-time analysis using high-resolution digital microscopy (HRDM), X-ray diffraction (XRD), X-ray fluorescence (XRF), and total organic carbon (TOC) assessment. By determining the mineralogical and geochemical structure and TOC content of drilled cuttings in near-real time, the rigsite service helps operators maximize the value of formation evaluation, support operational decisions, and minimize risk.

Provided laboratory-quality measurements in near-real time

Maersk’s subsurface team decided to conduct a trial of the GeoFlex service’s HRDM and XRD devices on legacy cuttings to confirm the possibility of achieving laboratory-quality mineralogical analysis at the wellsite.

For the trial, the subsurface team selected cuttings from a well drilled seven years prior in the Chissonga field offshore Angola. Clay-rich samples from the claystone above and below the top reservoir sand were chosen because LWD gamma ray and resistivity logs from this interval had a static response.

The team specifically wanted to determine if the GeoFlex service could identify any difference in the character of the claystone and identify formation tops. The selected samples were rich in clays and excluded reservoir sand samples. Despite this additional challenge, the GeoFlex service successfully provided lithofacies information that showed good correlation with laboratory analysis of core samples.

From the shallowest sample provided, the clay composition was shown to be unchanging for 310 m [1,017 ft]. At that point and over the next 120 m [394 ft], the GeoFlex service identified a decrease in illite and muscovite and an increase in kaolinite that were not detected by LWD gamma ray or resistivity logs. At 430 m [1,410 ft] from the shallowest sample, measurements from the GeoFlex service showed an increase in quartz, which is associated with the top reservoir.

Based on analysis from the GeoFlex service, Maersk determined that the results were comparable to whole-rock XRD laboratory analysis of core samples. As a result, Maersk identified the GeoFlex service as a wellsite technology superior to traditional mud logging.


Download: GeoFlex Service Identifies Subtle Mineralogical Differences in Clay-Rich Legacy Cuttings for Maersk (0.29 MB PDF)

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GeoFlex Service Identifies Subtle Mineralogical Differences in Clay-Rich Legacy Cuttings for Maersk
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