At-Surface Real-Time Isotope Logging Assesses Lateral Heterogeneity in Marcellus Shale | SLB
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United States, North America, Onshore
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Challenge: Evaluate rock and fluid heterogeneity along the lateral of a well in the Marcellus Shale.

Solution: Assess fluid and formation heterogeneity and obtain thermal maturity proxy at surface with isotope logging service providing continuous measurement of the isotopic ratio.

Results:

  • Provided a thermal maturity log that showed strong agreement with the official Marcellus vitrinite reflectance equivalent (VRE) map and that was confirmed by a separate study
  • Confirmed homogeneity of the fluid maturity and the formation
  • Enabled optimal development of unconventional reservoir
Products Used
Isotope Logging

At-Surface Real-Time Isotope Logging Assesses Lateral Heterogeneity in Marcellus Shale

Thermal maturity calculation from isotope logging service provides insight into hydrocarbon fluid type in place

Evaluate rock and fluid heterogeneity to identify the optimal landing point

In a horizontal development well targeting the Marcellus Shale, the operator needed to acquire accurate formation data. Specifically, the operator wanted to assess lateral heterogeneity of the fluid and rock to gain initial information for determining hydrocarbon fluid type in place.

Determine hydrocarbon fluid in place with thermal maturity log

Schlumberger proposed using isotope logging service to continuously measure isotopic ratios of d13C–CH4 from surface while drilling to produce a continuous thermal maturity log. A continuous thermal maturity log is the first step toward determining hydrocarbon fluid type in place, and providing this data would enable improved while-drilling reservoir management decisions. The isotope logging service, which poses no additional operational risk, would also help in identifying vertical and lateral discontinuities, including gradients and small-scale features. Acquiring this information is particularly challenging in unconventional reservoirs but would provide the initial information needed to determine hydrocarbon fluid type in place, improve geosteering, and increase the accuracy of target allocation.

Confirmed official VRE maturity map with real-time formation property information

The isotope logging service produced a thermal maturity log that showed very high stability along the lateral, confirming homogeneity of the fluid maturity and the formation.

The continuous maturity log, which measures VRE, closely matched the official Marcellus VRE maturity map for the well’s location. The fluid typing results from the isotope logging service were also confirmed by a detailed maturity study on gas spot samples (d13 of C1, C2, and C3).

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Comparing the isotope log thermal maturity proxy (vitrinite reflectance equivalent [VREq]) with the VRE map shows a perfect match within 10%–90% confidence (red arrow) ±0.09% VRE.
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Real-time measurement of δ13 of C1 from isotope logging clearly marks the entry into the Marcellus Shale from the overburden. The exit from the base limestone marked from other data sources reveals no maturity variation from δ13 of C1.
Products Used
Isotope Logging
Continuous δ13C–CH4 measurements in real time

Characterize the geological and geochemical hydrocarbon system in terms of source, generation, and subsurface behavior.

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