24-Pet-A1 Principles of Stratigraphy and Sedimentation · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 98-Pet-A1 Principles of Stratigraphy & Sedimentation, 2014-Dec. 3 hours duration; closed book, no calculator permitted. The paper has three parts: Part A1 (Questions 1–7, sedimentary processes, 5 marks each, answer any 4 of 7 for 20 marks), Part A2 (Questions 8–15, brief/multiple-choice, 3 marks each, answer any 5 of 8 for 15 marks), and Part B (Questions 16–24, stratigraphy, 5 marks each, answer any 6 of 9 for 30 marks) – a 65-mark maximum.
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); 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.
In a well-sorted rock, grains span a narrow size range, so there is little or no fine material available to fill the pore spaces between the framework grains; the result is high porosity and high permeability, with well-connected, relatively straight pore throats. In a poorly-sorted rock, a wide range of grain sizes are present together, and the finer grains pack into the pore spaces left by the coarser ones; this reduces total porosity, and – more severely – chokes and lengthens the connecting pore throats, so permeability drops far more sharply than porosity does (a poorly-sorted rock can retain moderate porosity but have very poor flow capacity). Sorting also governs how effectively later diagenetic cement can occlude the pore system: a well-sorted, well-connected pore network is more vulnerable to complete cementation (fewer, larger, more accessible throats), whereas a poorly-sorted rock's flow paths may already be so tortuous that cement has comparatively less additional damage still to do.
