24-Pet-A1 Principles of Stratigraphy and Sedimentation · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Petroleum Engineering, 17-Pet-A1 Principles of Stratigraphy & Sedimentation, 2018-May. 3 hours duration; closed book, no calculator permitted. The paper has two parts: Part A (Questions 1–10, Sedimentology and Sedimentary Processes) – Questions 1 and 2 are mandatory (10 marks each, 20 marks), plus any five of the remaining eight (3–10) at 6 marks each (30 marks), for a Part A total of 50 marks; and Part B (Questions 11–19, Stratigraphy and Sedimentary Basin Analysis) – answer any six of the nine at 5 marks each, for a Part B total of 30 marks – an 80-mark maximum (50 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 (sandstone/carbonate classification, diagenesis, dolomitization); Nichols, G., Sedimentology and Stratigraphy, 2nd ed., Wiley-Blackwell (fluvial/deltaic systems, sequence stratigraphy, stratigraphic units); Reading, H.G. (ed.), Sedimentary Environments: Processes, Facies and Stratigraphy, 3rd ed., Blackwell (facies models, deep-marine and shelf systems); Selley, R.C. & Sonnenberg, S., Elements of Petroleum Geology, 3rd ed., Academic Press (source rocks, basin classification, 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.
Well logs record a continuous, depth-registered physical property of the rock penetrated by a borehole; because the same regionally-persistent marker beds (commonly shales, coals or thin limestones) produce a recognizable, repeatable log signature, matching that signature "bed-for-bed" between wells is one of the most reliable subsurface correlation tools available, especially where core or cuttings control is sparse.
Gamma-ray (GR) log – records natural formation radioactivity (mainly from clay-hosted K, Th, U); shale/mudstone reads high GR, clean sandstone/carbonate/coal reads low GR, so a GR curve traces the shale-versus-clean stratigraphic pattern directly and is the standard correlation curve because it works in both open and cased holes and in any borehole fluid. Spontaneous potential (SP) log – records the natural electrochemical/electrokinetic potential generated where permeable, porous beds contact the (fresher) drilling mud filtrate against saline formation water; permeable sand deflects the SP curve away from a stable "shale baseline," giving a similarly reliable, if fluid-dependent, correlation marker.
