24-Pet-A1 Principles of Stratigraphy and Sedimentation · May 2013
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 98-Pet-A1 Principles of Stratigraphy & Sedimentation, 2013-May. 3 hours duration; closed book, no calculator permitted. Candidates answer any 10 of the 15 questions (10 marks each, 100 marks total) and are asked to illustrate answers with drawings wherever possible.
Reference texts: Boggs, S. Jr., Principles of Sedimentology and Stratigraphy, 5th ed., Pearson (texture classification, evaporites, clay minerals, sediment gravity flows, storm/shelf processes, bedforms, stable isotopes, geological time scale); Tucker, M.E., Sedimentary Petrology, 3rd ed., Blackwell (carbonate fabric, dolomitization, reef facies); Nichols, G., Sedimentology and Stratigraphy, 2nd ed., Wiley-Blackwell (depositional systems, transgression/regression, sequence stratigraphy); Reading, H.G. (ed.), Sedimentary Environments: Processes, Facies and Stratigraphy, 3rd ed., Blackwell (facies models); Selley, R.C. & Sonnenberg, S., Elements of Petroleum Geology, 3rd ed., Academic Press (source rock maturation, petroleum systems); International Commission on Stratigraphy, International Chronostratigraphic Chart (geological time scale).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
A petroleum source rock is a fine-grained sedimentary rock (shale, mudstone, or organic-rich marl/limestone) containing enough preserved organic matter to have generated, or be capable of generating, commercial quantities of oil and/or gas on burial and heating.
Organic matter – marine phytoplankton/zooplankton or terrestrial plant debris – is deposited along with fine clastic sediment in a setting combining high biological productivity (to supply enough organic matter) with restricted oxygen circulation and/or rapid burial (to prevent that organic matter being oxidized before it can be preserved) – classic settings include anoxic silled basins, upwelling-driven high-productivity continental margins, and stratified (anoxic bottom-water) lakes.
As the source rock is progressively buried and heated, its kerogen passes through three stages: diagenesis (shallow, <≈50 °C, biological/low-temperature reactions convert biopolymers into kerogen, generating only minor biogenic methane); catagenesis (roughly 60–150 °C, thermal cracking of kerogen generates first oil, through the oil window ≈60–120 °C, vitrinite reflectance Ro≈0.6–1.3%, then progressively drier gas through the gas window ≈120–150 °C as continued cracking breaks liquid hydrocarbons down further); and metagenesis (>150 °C, only dry methane and ultimately graphitic residue remain – the rock is overmature and can generate no more liquid hydrocarbon).
