Predicting Petroleum Physical Properties Using the NSO-Compounds Inventory of Pyrolysates

Abstract

During sediment burial macromolecular organic matter in source rocks is broken down into smaller petroleum compounds mainly consisting of polar Nitrogen-Sulphur-and-Oxygen (NSO)-containing compounds and hydrocarbons. This complex mixture can be either expelled into the carrier system to form conventional oil and gas reservoirs or stay behind to form unconventional reservoirs. To formulate appropriate production strategies of petroleum from either of these reservoirs our goal is to be able to predict the physical properties of generated, retained, and migrating fluids, which in turn are defined by the detailed chemical composition of the petroleum fractions. To assess the bulk composition of first-formed petroleum is hereby key because all subsequent processes such as fractionation during expulsion, retention, and production simply act upon the original composition. Using preparative pyrolysis methods and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) as the detection method for NSO compounds we aim, in close analogy to the PhaseKinetics approach [1], to establish the role played by the asphaltenes and resins fraction in controlling the physical properties of fluids expelled into conventional reservoirs and of fluids retained in unconventional reservoirs. Up to now, off-line open-system pyrolysis was run for more than twenty immature and early mature source rocks from various depositional environments and prolific petroleum basins worldwide, whereas pyrolysates were measured using ESI-FT-ICR MS in the negative ion mode. We included Permian source rock pairs from South America and South Africa (Irati and Whitehill Fm.) as well as Cretaceous source rocks from the Orange Basin. Using bulk NSO-compounds compositions as well as target compounds and proxies from individual elemental classes (e.g. carbon number distribution within the N1 elemental class [2] or DBE distribution within the O2 class), petroleum type organofacies fields [1] can be established and linked to physical properties such as GOR and API gravity. We will present how to use the full inventory of pyrolysate NSO-compounds of a given source rock to predict the derived fluids behaviour within their respective reservoir. References [1] di Primio and Horsfield (2006), AAPG Bulletin 90, 1031-1058. [2] Mahlstedt et al. (2016), Energy and Fuels 30, 6290-6305.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018