24-Pet-A1 Principles of Stratigraphy and Sedimentation · December 2015
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 98-Pet-A1 Principles of Stratigraphy & Sedimentation, 2015-Dec. 3 hours duration; closed book, no calculator permitted. The paper has two parts: Part A (Questions 1–11, sediments/sedimentary rocks/sedimentary processes – Questions 1–4 at 10 marks each and Questions 5–11 at 5 marks each; answer any combination of questions totaling 45 marks) and Part B (Questions 12–18, stratigraphy – Questions 12–14 at 10 marks each and Questions 15–18 at 5 marks each; answer any combination totaling 30 marks) – a 75-mark maximum (45 for Part A + 30 for Part B).
Reference texts: Boggs, S. Jr., Principles of Sedimentology and Stratigraphy, 5th ed., Pearson (grain texture, sediment transport, bedforms, carbonate/evaporite systems, sequence stratigraphy, unconformities, stratigraphic principles); Tucker, M.E., Sedimentary Petrology, 3rd ed., Blackwell (carbonate classification, diagenesis, dolomitization); Nichols, G., Sedimentology and Stratigraphy, 2nd ed., Wiley-Blackwell (fluvial systems, sequence stratigraphy, stratigraphic units); Reading, H.G. (ed.), Sedimentary Environments: Processes, Facies and Stratigraphy, 3rd ed., Blackwell (facies models, trace fossils, coastal processes); Selley, R.C. & Sonnenberg, S., Elements of Petroleum Geology, 3rd ed., Academic Press (source rocks, reservoir quality); 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) Sandstone components. Framework grains – the sand-sized (1/16–2 mm) clastic particles forming the rock's load-bearing skeleton: quartz (monocrystalline and polycrystalline), feldspar (K-feldspar, plagioclase), and lithic (rock) fragments (volcanic, sedimentary or metamorphic clasts). Matrix – very fine-grained (silt/clay) material occupying the pore space between framework grains, deposited together with the sand (detrital) rather than precipitated later. Cement – minerals precipitated chemically from pore fluids after deposition (diagenetically) that bind the framework grains together, most commonly quartz overgrowths, calcite, and clay or iron-oxide coatings.
(c) QFL ternary classification. Sandstones are classified by plotting the recalculated-to-100% proportions of Q (total quartz – monocrystalline, polycrystalline, and chert), F (total feldspar) and L (total unstable lithic fragments) on a triangular diagram, so that every sample plots as a single point. The principal fields are quartz arenite (Q>90%, matrix-poor, texturally and mineralogically mature), arkose (F>25% and F>L, a feldspar-rich sand near a granitic/gneissic source) and litharenite (L>25% and L>F, rich in unstable rock fragments); a matrix-rich (>15% clay matrix) variant across this same Q-F-L spectrum is classified separately as greywacke.
