Reactivation of cation exchange properties in black shales (original) (raw)
Related papers
Elucidation of the Alum Shale kerogen structure using a multi-disciplinary approach
Organic Geochemistry, 1995
The significance and validity of integrating data obtained from a variety of analytical techniques to understand, elucidate and model kerogen's complex chemical structure is reported here using degradative (open and closed system pyrolysis, chemical oxidation), non-degradative ("C CP/MAS NMR) and optical (incident white light and blue light) methods. Seven Cambrian Alum Shale samples, ranging in maturity from immature to post-mature with respect to petroleum generation, were studied and were chosen for their simple geological history, uniform organic matter type and high organic carbon content. The Alum Shale kerogens, which primarily consist of algal organic matter, liberate low molecular weight gaseous and aromatic compounds on pyrolysis and give mostly branched dicarboxylic acids on chemical oxidation. "C NMR spectroscopy shows that the Alum Shale kerogens arc anomalously rich in oxygen-bearing functional groups (such as C = 0, ArCO, CHO, CH,O), most of which apparently remain intact within the kerogen macro-molecule (KMM) through the diagenetic and catagenetic stages. Fragments released by different degradative techniques are quantified and the aromaticity (E), O/C and relative proportions of various carbon types estimated by "C NMR. A synthesis of these data has allowed us to better understand the chemistry of the Alum Shale kerogen.
—The increasing exploration and exploitation of hydrocarbon resources hosted by oil and gas shales demands the correct measurement of certain properties of sedimentary rocks rich in organic matter (OM). Two essential properties of OM-rich shales, the total specific surface area (TSSA) and cation exchange capacity (CEC), are primarily controlled by the rock's clay mineral content (i.e. the type and quantity). This paper presents the limitations of two commonly used methods of measuring bulk-rock TSSA and CEC, ethylene glycol monoethyl ether (EGME) retention and visible light spectrometry of Co(III)-hexamine, in OM-rich rocks. The limitations were investigated using a suite of OM-rich shales and mudstones that vary in origin, age, clay mineral content, and thermal maturity. Ethylene glycol monoethyl ether reacted strongly with and was retained by natural OM, producing excess TSSA if calculated using commonly applied adsorption coefficients. Although the intensity of the reaction seems to depend on thermal maturity, OM in all the samples analyzed reacted with EGME to an extent that made TSSA values unreliable; therefore, EGME is not recommended for TSSA measurements on samples containing >3% OM. Some evidence indicated that drying at 5200ºC may influence bulk-rock CEC values by altering OM in early mature rocks. In light of this evidence, drying at 110ºC is recommended as a more suitable pre-treatment for CEC measurements in OM-rich shales. When using visible light spectrometry for CEC determination, leachable sample components contributed to the absorbance of the measured wavelength (470 nm), decreasing the calculated bulk rock CEC value. A test of sample-derived excess absorbance with zero-absorbance solutions (i.e. NaCl) and the introduction of corrections to the CEC calculation are recommended.
Organic structural properties of kerogen as predictors of source rock type and hydrocarbon potential
Fuel
This study improves upon previously identified correlations between the chemical structure of kerogen and potential hydrocarbon (oil and gas) yields assayed by Rock-Eval pyrolysis. We propose a quantitative structure-catagenesis relationship that predicts the hydrocarbon generation potential of source rocks and of lacustrine, marine, and terrestrial origin (types I, II, and humic coals). We used one-dimensional solid-state 13 C Nuclear Magnetic Resonance (13 C NMR) spectroscopy with 1 H spectral editing to determine the abundance of carbon functional groups, including non-protonated and mobile groups. An NMR-based van Krevelen analysis readily separated the kerogen types. Single regression matrices of NMR-based structure parameters against Rock-Eval hydrocarbon yield revealed distinct dynamics of the kerogen types upon pyrolysis. Multiple regression showed that alkyl, oxygen-substituted alkyl, and carbonyl groups were strong contributors to hydrocarbon production, while oxygen-substituted aromatic carbons were strongly counterproductive. Catagenetic relationships established for kerogen provide insight into kerogen structure evolution upon pyrolysis, and can more closely constrain the mechanisms of hydrocarbon generation for use in sedimentary basin modelling.
Journal of the Serbian Chemical Society, 2008
A 29-step alkaline permanganate degradation of type III kerogen from Tyrolean (Hahntennjoch, Austria) oil shale was performed. A high yield of oxidation products was obtained (93.7 % relative to the original kerogen): 0.5 % neutrals and bases, 19.5 % ether-soluble acids and 58.9 % of precipitated (PA). A substantial amount of kerogen carbon (14.8 %) was oxidized into carbon dioxide. The organic residue remaining after the final oxidation step was 6.9 %. The PA components were further oxidized and the total yields relative to original PA were 1.0 % neutrals and bases and 59.0 % ether-soluble acids, the non-degraded residue being 29.3 %. Detailed quantitative and qualitative analysis of all oxidation products suggested the Tyrolean shale kerogen to be a heterogeneous macromolecular substance consisting of three types of structures differing in composition and susceptibility towards alkaline permanganate: the first, resistant, presumably composed of aromatic structures linked by resorcinol ethereal bonds; the second, combined in nature, the aliphatic part comprising methyl-substituents and short cross-links, both easily oxidized into CO 2 , water and low molecular weight acids and aromatic structures yielding aromatic di-and tri-carboxylic acids as oxidation products; finally the third, composed of aliphatic cross-links and substituents, alicyclic (and/or heterocyclic) and some aromatic structures, bound into units moderately resistant towards oxidation. The overall yields of kerogen and PA oxidation products lead towards a balance between aromatic, alkane mono-and dicarboxylic and alkanepolycarboxylic acids, suggesting a shift of the structure of Tyrolean shale kerogen from typical aromatic reference type III towards a heterogeneous aromatic-aliphatic-alicyclic type structure.
Journal of South American Earth Sciences, 2020
Shale samples from outcrops of the Irati Formation (Permian), Paraná Basin, Brazil were analyzed based on organic geochemistry, palynofacies, and stable carbon isotopes with the aim of evaluating thermal effects of igneous intrusions on the kerogen. The potential for hydrocarbon generation, the depositional paleoenvironment, and the input of the organic matter were also studied. Most samples have high total organic carbon content, excellent hydrocarbon source potential, and type I kerogen, except some samples which showed changes in their compositional characteristic due alteration in the depositional paleoenvironment and due to the high maturation caused by the heat of diabase intrusions. The composition and distribution of saturate and aromatic biomarkers and stable carbon isotopes provided evidence that the composition of organic matter in the shales is marine, except at the upper part of the outcrops where the shales have contribution of terrestrial organic matter. Saturate biomarkers results indicated thermal immaturity for hydrocarbon generation, except the samples that were influenced by the heat of intrusive rocks.
Organic Geochemistry, 2001
A kerogen, termed aBS base, from the Gorodische section (Russian Platform) was studied using a combination of microscopic, spectroscopic and pyrolytic methods in order to determine its chemical structure, source organisms and formation pathway(s). This kerogen was mainly formed via degradation-recondensation of phytoplanktonic material. Selective preservation and natural sulphurisation pathways only played a minor role, whereas a substantial contribution of ether linked lipids was noticed, revealing large oxygen cross-linking. Such observations allowed us to put forward, for the first time to the best of our knowledge, a substantial role for the oxidative reticulation pathway in the formation of a kerogen. Comparision with a previously studied sample from the same outcrop revealed contrasting features which reflect differences in preservation pathways triggered by different depositional conditions. #
AAPG Bulletin, 2012
Evaluations of porosity relevant to hydrocarbon storage capacity in kerogen-rich mudrocks (i.e., source rocks) have thus far been plagued with ambiguity, in large part because conventional core and petrophysical techniques were not designed for this rock type. The growing recognition of an intraparticle organic nanopore system that is related to thermal maturity is beginning to clarify this ambiguity. This mode of porosity likely evolved with the thermal transformation of labile kerogen and probably neither depends nor interacts (except perhaps chemically) with previously assumed "matrix" or "mineral" porosity that is dominated by bound water, and that may be largely irrelevant to hydrocarbon storage capacity in these rocks. To address this newly recognized and important nonmatrix kerogen pore system, that is arguably the dominant hydrocarbon storage and mobility network in these rocks, we introduce a relatively simple kinetic model that describes porosity development within kerogen as a function of thermal maturation. Kerogen porosity development is estimated within the upper Albian Mowry Shale in the Powder River Basin of Wyoming to illustrate the approach. Relevant storage capacity is considered to have evolved with thermal decomposition of organic matter during catagenesis, where we estimate that kerogen porosity does not typically exceed 3% of bulk rock volume.