Heterogeneity of Organoclay Complexes in Shale Regulates the Generation of Shale Oil

TL;DR

The study shows how organoclay complexes in shale affect the formation and mobility of shale oil, with mineral evolution playing a key role.

Contribution

The paper introduces a new perspective on shale oil generation by linking mineral evolution and organoclay heterogeneity to hydrocarbon yield.

Findings

Shale oil yield is influenced by mineral evolution and OM desorption, not just OM content.

Higher illitization in deeper intervals increases hydrocarbon mobility and saturate proportions.

Shallower intervals with abundant OM produce limited shale oil due to stabilized adsorbed OM.

Abstract

Organic matter (OM)
and clay minerals are important components
in shale, which are intimately associated with each other in the form
of organoclay complexes. The diverse mineral-OM associations result
in varying OM occurrences, which possess distinct hydrocarbon generation
potential and ultimately affect the accumulation of shale oil. Therefore,
the investigation of the heterogeneity of organoclay complexes is
crucial to gaining a comprehensive understanding of the varying exploration
potential of shale oil resources. In the present study, shale samples
from three intervals in Dongying Depression were collected to investigate
the mineralogical and organic characteristics of the organoclay complexes,
aiming to explore their impact on the yield and composition of shale
oil. Results showed that the smectite gradually converted into illite,
which was accompanied by the release of OM from clay mineral interlayers
and the desorption of chemically adsorbed OM. The yield and composition
of shale oil cannot solely be explained by the OM content and types
in the shale. Instead, they are intricately linked to the evolution
of minerals and OM occurrence. From the perspective of the heterogeneity
of organoclay complexes, despite the abundant OM content in shallower
intervals (Es3x), the shale oil formation remains limited due to the
low degree of mineral evolution and the stabilization of the adsorbed
OM by clay minerals. Consequently, this leads to a higher proportion
of resin, which is not conducive to the mobility of shale oil. In
contrast, despite the OM content varying slightly in the deeper interval
(Es4s), the elevated smectite illitization degree promotes the desorption
of OM and its conversion into hydrocarbons. This results in a substantial
increase in shale oil formation and a higher proportion of saturates,
greatly enhancing the mobility of shale oil. These findings are profoundly
significant for understanding shale oil generation and accumulation.

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