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24-Pet-B4 Well Testing · December 2014

Question 14 of 18: Simple anticline trap cross section

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

EGBC National Exam — Petroleum Engineering, 2014-Dec. 3 hours duration; closed book. This sitting's own cover page reads “98-Pet-B4, Petroleum Geology” and every question is descriptive/interpretive petroleum geology (source rocks, generation, migration, traps, Canadian basin geography) – no well-test pressure-transient content anywhere. Five (5) of the paper's six 20-mark sections are marked (NOTES item 5); all six are solved in full below so this set also serves as a complete study reference. The paper is almost entirely qualitative (draw/describe/define/list), with one true numeric calculation (Q3-2, capillary seal-breach column height).

Reference texts: Selley, R.C. & Sonnenberg, S., Elements of Petroleum Geology, 3rd ed., Academic Press (source rocks, migration, traps); Tissot, B.P. & Welte, D.H., Petroleum Formation and Occurrence, 2nd ed., Springer (kerogen typing, oil/gas windows, primary migration); Boggs, S. Jr., Petrology of Sedimentary Rocks, 2nd ed., Cambridge (source-rock lithofacies); Allen, P.A. & Allen, J.R., Basin Analysis: Principles and Applications to Petroleum Play Assessment, 3rd ed., Wiley-Blackwell (extensional basins, structural styles); Biddle, K.T. & Wielchowsky, C.C., “Trap Types in Petroleum Basins,” AAPG Memoir 60, ch.12 (stratigraphic/structural/salt trap classification); Mossop, G.D. & Shetsen, I. (eds.), Geological Atlas of the Western Canada Sedimentary Basin, CSPG/Alberta Research Council, 1994 (WCSB stratigraphy and play types).

Section 5, Q5-2: Simple anticline trap cross section (5 marks)

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.

Simple anticline trap GAS OIL WATER GOC OWC shale caprock (seal) sandstone reservoir
A simple, symmetric anticline – a folded reservoir bed (sandstone) draped by a low-permeability caprock (shale). Gas (least dense) occupies the crest above the gas–oil contact (GOC), oil occupies the flanks between the GOC and the oil–water contact (OWC), and water fills the reservoir below the OWC and beyond the structural closure. Turner Valley, Alberta – a faulted west-dipping anticline discovered in 1914, Canada's first major oil/gas field – is a classic anticlinal-trap example.

An anticline is the simplest structural trap: reservoir and seal beds are folded upward into a closed, four-way dip closure, and buoyancy segregates the fluids so gas (if present) caps the crest, oil occupies the section below the gas–oil contact down to the oil–water contact, and water occupies the reservoir below and beyond the structural closure. Turner Valley, Alberta (discovered 1914, a west-dipping, faulted anticline in Mississippian Rundle Group carbonates sealed by overlying shale) is a well-known Canadian example; the Kirkuk Field (Iraq) is the classic international example of a very large, simple anticlinal trap.