Examples of each stratigraphic trap type: 24-Pet-B4 Well Testing, Undated paper, Q11

Question 11 of 13: Examples of each stratigraphic trap type

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

Notes on this paper

EGBC National Exam — Petroleum Engineering, 17-Pet-B4 (May 2019, per its page footers). 3 hours duration; closed book. This paper's own cover page reads “17-Pet-B4, Petroleum Geology” and all five sections are descriptive/interpretive petroleum geology (terminology, source rocks, thermal maturation, stratigraphic traps, structural traps), no well-test pressure-transient content anywhere. The section marks are Section 1 = 30, Section 2 = 18, Section 3 = 22, Section 4 = 15, Section 5 = 15 (sum 100), used throughout below. The exam is entirely qualitative (explain/define/sketch).

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

Section 4, Q4-3: Examples of each stratigraphic trap type (3 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.

Facies-change (pinch-out) trap: the Rainbow (Devonian) pinnacle reef trend of northwestern Alberta, WCSB – isolated reef buildups encased in impermeable Muskeg Formation evaporite/shale.

Unconformity trap: the sub-Cretaceous unconformity beneath the Lower Cretaceous McMurray Formation, Athabasca oil sands, Alberta – bitumen-saturated McMurray valley-fill/channel sands truncate against, and onlap, the sub-Cretaceous unconformity surface (a classic international example is the East Texas Field, USA, a truncation trap at the same type of sub-Cretaceous unconformity).

Diagenetic trap: the Nisku Formation (Devonian) dolomitized reef and shoal reservoirs of west-central Alberta, WCSB – secondary dolomitization created porosity and permeability within an originally tight limestone.

Topic. Named field/trend examples illustrating each stratigraphic trap type in the WCSB and internationally.

Key relations. All three examples are Devonian–Cretaceous plays in the Western Canada Sedimentary Basin, showing that the same basin can host all three stratigraphic trap types in different stratigraphic intervals.

Why this works. Naming a real trend/field for each mechanism demonstrates that the classification (Q4-1) is not just conceptual – each type corresponds to an actual, commercially significant play with its own characteristic exploration risk.

Common pitfall. Citing a STRUCTURAL trap (e.g. an anticline) as a stratigraphic example – the question specifically wants a play whose closure is stratigraphic (facies/unconformity/diagenetic), not one that also happens to sit on a fold or fault.

Source. Mossop & Shetsen (eds.), Geological Atlas of the Western Canada Sedimentary Basin, CSPG/ARC, 1994, ch.14 (Rainbow reef play), ch.30 (Athabasca oil sands), ch.16 (Nisku reef/dolomite play).