Silica diagenesis promotes early primary hydrocarbon migration

Abstract

We present evidence that hydrocarbon source rocks can be preconditioned for primary hydrocarbon migration at an early stage of catagenesis by pore-scale processes linked to silica diagenesis. The evidence comes from a detailed petrographic and geochemical study of the Jordan Oil Shale (JOS), an immature to early mature, Upper Cretaceous to Paleogene source rock developed on the platform regions of central and southern Jordan. Diagenesis of biogenic silica led to silicification of the source rock interval and the growth of chert nodules. Localization of bitumen veins in reaction rims around these nodules is interpreted to indicate that silica diagenesis promotes the early mobilization of hydrocarbons from the geochemically identical, disseminated bitumen within the host mudstones. We propose a model in which early-formed bitumen migrated into neoforming mode I fractures that formed as a result of the crystallization pressure imposed from the growing chert nodule. Hydraulic fracturing occurred under elevated bitumen fluid pressures that approached lithostatic stress values under burial depths of the order of 1000 m. The recognition that silica diagenesis can promote the early migration of neoforming bitumen raises the possibility that primary hydrocarbon migration may occur earlier and at shallower depths than predicted by kinetic modeling approaches wherever silica diagenetic reactions are coeval with catagenesis.

Modelling the initiation of bitumen-filled microfractures in immature, organic-rich carbonate mudrocks: The Maastrichtian source rocks of Jordan

“…1b). TOC content ranges from 3 to 30 wt% (Hakimi et al, 2016;Abu-Mahfouz et al, 2019, 2020. The Hydrogen Index (HI) and Rock-Eval T max data suggest that organic matter is predominantly Type I/II S Kerogen, indicating a marine origin (Fig.…”

“…Hydrocarbons, in the form of bitumen, have been documented within multiscale fracture sets in a few studies, including microfractures developed during early catagenesis (e.g., Ryder et al, 2013;, 2020. Understanding the very first generation of these bitumen microfractures is critical, as they provide the first network of pathways during the primary migration of hydrocarbons and pore-matrix connection in unconventional reservoirs.…”

“…Previous studies on these source rocks have focused on their organic matter enrichment, maturation, hydrocarbon potential, sedimentological, and paleoenvironmental implications (e.g., Abed and Al-Arouri., 1994;Abed et al, 2009;Ali Hussein et al, 2014a;März et al, 2016;Hakimi et al, 2016Hakimi et al, , 2018. Only very few studies have focused on the bitumen disseminated in the matrix and filling hosted fractures (Abu-Mahfouz et al, 2019, 2020. Abu-Mahfouz et al (2019) conducted a comprehensive geochemical investigation of bitumen fractures in these Upper Cretaceous Source Rocks and presented a conceptual model favouring the development of bitumen fractures by hydraulic fracturing.…”

Hyrous Pyrolysis of Source Rock Plugs: Geochemical and Visual Investigations and Implications for Primary Mirgation

“…If the fracture criteria are reached, micro-fracturing of the rock occurs, thereby providing new migration pathways. Such microfractures have been frequently observed in petroleum source rocks of different maturity levels (Littke et al, 1988;Abu-Mahfouz et al, 2019, 2020. The conversion of solid kerogen towards liquid hydrocarbons itself creates new void space, which can facilitate pressure-driven migration.…”

Role of Organic Matter, Mineral, and Rock Fabric in the Full-Scale Pore and Fracture Network Development in the Mixed Lacustrine Source Rock System

“…The total organic carbon (TOC), mineral components, and maturity stage of shale affect the pore structure parameters and hydrocarbon primary migration. − A productive shale system should contain sufficient organic matter to support a percolating network, and this organic matter should be mature to build a pore system that percolates over a sufficiently large length scale . Apart from the above parameters, lamina development is a widespread phenomenon in natural sedimentary rock. − The effect of laminae development is significant on the pore structure and intrasource migration of lacustrine shale. − Li et al presented that microfracture occurrence was at the boundary of laminae, and laminated shale had a better connectivity than massive Shahejie mudstone in Zhanhua Sag, Eastern China. Lei et al analyzed the difference between silty laminae and clay laminae of Zhangjiatan Shale in the Ordos Basin.…”