24-Pet-B4 Well Testing · December 2014
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
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).
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.
Preserving organic matter requires two things working together: high biological productivity (a large supply of organic matter) and a depositional environment where that organic matter is not destroyed by oxidation before burial – almost always because bottom waters are anoxic or dysoxic, so aerobic decomposers and bioturbating organisms cannot operate. Four classic settings satisfy this combination:
1. Deep, thermally stratified lake (lacustrine). In a deep rift or graben lake, warm, low-density surface water (epilimnion) sits over cold, denser bottom water (hypolimnion), separated by a thermocline that prevents vertical mixing. Algal productivity in the sunlit epilimnion is high, but because the water column never overturns, the bottom water becomes anoxic as dissolved oxygen is consumed by decay of the settling organic rain and never replenished – organic matter (algal, Type I kerogen) is preserved rather than oxidized. Example: East African rift lakes, or the Green River Fm (Eocene, western USA) analogue.
2. Silled (restricted) marine basin. A basin partly enclosed by a sill (a submarine ridge, reef, or structural high) restricts exchange with open, oxygenated ocean water below sill depth. Combined with high surface productivity and often some freshwater influx creating salinity stratification, the deep water in the basin stagnates and turns anoxic (euxinic, often H2S-bearing), preserving marine (Type II) organic matter on the basin floor undisturbed by bioturbation. Example: the modern Black Sea; the Jurassic Kimmeridge Clay of the North Sea.
3. Coastal-upwelling continental shelf. Where prevailing winds drive Ekman transport of surface water offshore, cold, nutrient-rich deep water upwells onto the shelf, fuelling exceptionally high phytoplankton productivity. The resulting high biological oxygen demand from decaying organic matter, combined with sluggish deep circulation, produces a mid-water oxygen-minimum zone that impinges on the shelf/upper slope, preserving organic-rich mud there even though the basin as a whole is open marine. Example: the modern Peru–Chile and Benguela upwelling systems; the Monterey Fm (California).
4. Deltaic / paralic swamp. In the low-energy, vegetated back-swamp and marsh environments of a delta plain, very high terrestrial plant productivity combines with waterlogged, oxygen-poor soils (peat mires) where decay is slow and incomplete, and with the delta's own high sedimentation/subsidence rate, which buries the organic matter quickly before it can fully oxidize. This setting preserves terrestrial (Type III, humic/coaly) organic matter and is the classic source of gas-prone kerogen and coal. Example: the Mahakam Delta (Indonesia); the Mannville coals of the WCSB.
