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.
SLB proposed using isotope logging service to continuously measure isotopic ratios of δ13C–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.
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 (δ13 of C1, C2, and C3).
![Graph: At-Surface Real-Time Isotope Logging Assesses Lateral Heterogeneity in Marcellus Shale - 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.](/-/media/files/drilling/case-study/isotope-logging-marcellus-shale-cs-1a.ashx)
