Browsing by Author "Cesar, Jaime"
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- ItemOpen AccessMolecular and stable carbon isotope geochemistry of mud-gas-derived hydrocarbons and its application for the assessment of low-permeability reservoirs from the Montney Formation, Western Canada(Elsevier, 2022-01-03) Cesar, Jaime; Mayer, Bernhard; Becker, Veith; Nightingale, Michael; Ardakani, Omid H.Mud-gas isotope logging (MGIL) of hydrocarbons (methane, ethane, propane) has become a widely used approach to fingerprint gas-bearing formations during the drilling of vertical and horizontal oil and gas wells often with the goal to assess potential cross-formational gas migration. In this study, we have used mud-gas molecular and isotope data to assess the usefulness of MGIL for the geochemical assessment of a single low-permeability reservoir formation, the Montney Formation in Western Canada. An example from a well completed in British Columbia shows that hydrocarbon samples collected in IsoJars® tend towards more positive carbon isotope ratios compared to data for samples obtained using IsoTubes®, potentially attributed to 13C enriched residual gas retained in the cuttings. Additionally, in publically available mud-gas data from 45 other wells, it was found that the carbon isotope ratios of mud-gas from the Montney Formation are overall consistent with the thermal maturity of this stratigraphic unit, but the data display a relatively scattered trend on a thermal maturity plot based on Δ13CC1-C2 and Δ13CC1-C3. Molecular parameters such as [C1/(C2 + C3)] can be modified via processes such as desorption and diffusion after sampling gases in IsoJars®, while the i-C4/n-C4 ratio was found to be the most consistent molecular parameter between sampling techniques. We conclude that mud-gas molecular and isotope data derived from samples collected in IsoTubes® are suitable for geochemical assessment (e.g. thermal maturity, fluid–fluid correlations) of low permeability hydrocarbon reservoirs such as the Montney Formation.
- ItemOpen AccessOrganic and isotope geochemistry analysis of petroleum condensates from the unconventional portion of the Montney Formation, Western Canada(Elsevier, 2020-08) Cesar, Jaime; Becker, Veith; Mayer, BernhardThe Montney Formation is a rather complex petroleum reservoir because it contains in-situ and migrated hydrocarbons. Previous organic geochemistry studies reported for this play were based on biomarker ratios of petroleum fluids from the conventional part of this reservoir. Furthermore, there is no isotope study on liquid hydrocarbons from this formation reported to this date. Therefore, we determined the organic and isotope geochemistry of condensate petroleum from the unconventional portion of the Montney Formation to fill this knowledge gap. The condensates were found to be normal fluids of increasing thermal maturity with increasing depth and from the northeast to the southwest. Light hydrocarbon parameters such as paraffinicity (n-C7/methylcyclohexane) and aromaticity (toluene/n-C7) showed to be governed by thermal maturity according to the known maturity trends (increasing depth, and northeast to southwest). The molecular fingerprint of the condensates is to some extent bimodal (noticeable at n-C13) suggesting the possibility of two hydrocarbon charges in the reservoir. This is further evidenced by the stable carbon isotope profile of n-alkanes where light hydrocarbons (C8-C13) show a normal distribution (decreasing δ13C with carbon number) whereas heavier compounds (C19+) show a reverse trend (increasing δ13C with carbon number). We suggest that condensate petroleum produced in the study area corresponds to a mixture of hydrocarbons sourced by the Montney Formation plus alteration products from a pre-existing oil charge that migrated into Montney reservoirs before further burial and thermal maturation of this rock. Producing intervals were distinguished using the δ13C values of n-C11, n-C12, n-C22, and n-C23.
- ItemOpen AccessStable carbon isotope systematics of methane, ethane and propane from low-permeability hydrocarbon reservoirs(Elsevier, 2020-10-10) Cesar, Jaime; Nightingale, Michael; Becker, Veith; Mayer, BernhardWe have reassessed the stable carbon isotope systematics of methane (C1), ethane (C2), and propane (C3) in more than 500 natural gas samples from low-permeability hydrocarbon reservoirs around the world, with the purpose of providing new tools for thermal maturity assessment of natural gas that is increasingly produced from such reservoir types world-wide. A low-permeability reservoir resembles a semi-closed system and we found that the stable carbon isotope distribution in C1-C3 alkanes differs partially from what has been previously observed in natural gas from conventional hydrocarbon accumulations (e.g. C isotope distributions dominated by Rayleigh distillation and kinetic isotope effects). In a low-permeability reservoir, isotope exchange may play a more prominant role in the carbon isotope distribution, driving the system towards an even isotopic distribution (EID) of 6‰ between methane and ethane, and ethane and propane, at Ro of 1.5%. At higher maturity, ethane and propane depleted in 13C are formed as a consequence of thermal cracking of wet-gas components and possibly free radical decomposition/polymerization reactions, which leads to the occurrence of isotope reversals (δ13CC2 < δ13CC1 < δ13CC3, δ13CC2 < δ13CC3 < δ13CC1 and δ13CC3 < δ13CC2 < δ13CC1) at thermal maturity higher than 2.0%Ro. The diagram of the isotopic differences ∆13CC1-C2 (δ13CC1-δ13CC2) versus ∆13CC1-C3 (δ13CC1-δ13CC3) provides a new tool for classification of natural gas from low-permeability hydrocarbon reservoirs according to thermal history in three main regions: normal trend (subdivided into immature, oil/wet-gas window, and dry gas window), ethane reversal, and propane reversal with respect to methane. This new tool can be used to assess the maturity of the petroleum fluids and can assist in identifying hydrocarbon mixing.