Application of Diamondoids for Correlation of Very Mature Oil and Oil-Mixtures

Abstract

While biomarkers have proven to be the standard for oil-oil and oil-source rock correlation there are limitations. Very mature oil or condensate generated in the late oil window/wet gas window often contains insufficient biomarker concentrations to carry out reliable correlations. It is also difficult to accurately assess oil maturity when biomarkers are absent. Oil produced from unconventional wells is particularly prone to high maturity and diminishing returns from biomarker analysis. In contrast, diamondoids are concentrated more and more with increasing maturity becoming an important resource for both maturity assessment and correlation for highly mature fluids and source rocks. Furthermore, in mixed oil, while biomarkers might reveal the less mature component, diamondoids will be necessary to determine the more mature one.

We have applied diamondoid maturity assessment by quantitative diamondoid analysis (QDA) and oil correlation using distributions of large diamondoid molecules (QEDA) and compound specific isotope analysis of diamondoids (CSIA-D) on source rocks and oil produced conventionally and unconventionally.

Differentiation of fluids produced from the onshore Gulf of Mexico, including the Eagle Ford, Glen Rose, Bossier, Haynesville and Pearsall Formations, as well as some mixtures, have been determined. All these oil samples were without biomarkers and extremely mature, but source differentiation was clearly determined by diamondoids. Very mature source rocks from the Eagle Ford Formation were also analyzed by QEDA and CSIA-D showing facies differentiation in the well core. Various levels in the core were shown to contribute to oil being produced from local unconventional wells drilled laterally through the Eagle Ford. In the Permian Basin, mixtures of very mature oil from the Ellenburger (Ordovician), Woodford (Devonian) and Pennsylvanian sources were de-convolved and allocated by using QEDA.

Oil-to-oil and/or oil-to-source rock correlations have been established by using QEDA and CSIA-D with samples from unconvertional plays throughout Texas, Niobrara source rocks and oils, Permian Basin produced oils and oil mixtures, Alaska’s north slope, the Williston Basin, the Mexican Gulf of Mexico, Nova Scotia - Canada, Kuwait, and offshore Brazil. Extracts from over-mature source rocks with estimated vitrinite reflectance as high as 3.0 % Ro have been fingerprinted for correlation with fluids by the QEDA methods.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018