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24-Pet-B4 Well Testing · Undated paper

Question 4 of 13: Kerogen types on a “modified” Van Krevelen diagram

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 2, Q2-3: Kerogen types on a “modified” Van Krevelen diagram (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.

Kerogen-type evolution: van Krevelen (left) and modified (HI-OI) van Krevelen (right) O/C (atomic) H/C (atomic) 0 0.1 0.2 0.3 0 0.5 1.0 1.5 I II III increasing maturity → OI (mg CO₂/g TOC) HI (mg HC/g TOC) 0 100 200 300 0 300 600 900 I II III increasing maturity →
Left: the classical Van Krevelen diagram (atomic H/C vs. O/C), where each kerogen type begins at a characteristic H/C–O/C position and evolves down and to the left toward the origin as maturation progressively strips hydrogen (as generated hydrocarbon) and oxygen (as CO2/H2O). Right: the “modified” Van Krevelen diagram built from Rock-Eval pyrolysis data – Hydrogen Index (HI) vs. Oxygen Index (OI) – which is the practical, routinely-measured proxy for the same atomic H/C–O/C trend (Q2-4).

On the classical (atomic) Van Krevelen diagram, Type I plots at high initial H/C (≈1.5+) and very low O/C (≈0.03–0.1); Type II plots at moderately high H/C (≈1.2–1.5) and low–moderate O/C (≈0.1–0.2); Type III plots at low H/C (≈0.7–1.0) and moderate–high O/C (≈0.2–0.3). All three curves converge toward the origin (H/C → 0, O/C → 0) with increasing thermal maturity, since generation itself is the loss of hydrogen (as oil/gas) and oxygen (as CO2/H2O) from the kerogen.