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24-Pet-B4 Well Testing · December 2016

Question 9 of 22: Two methods for developing a bitumen-saturated sandstone reservoir – SAGD and CSS

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

Notes on this paper

EGBC National Exam — Petroleum Engineering, 2016-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, hydrocarbon chemistry, oil sands and tight-oil development, shale gas and coalbed methane, carbonate traps, siliciclastic/deltaic traps) – 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. This sitting's Section 6 is a Siliciclastic Traps section (wave-dominated delta, grain-size–permeability–porosity relations, sandstone diagenesis). The paper is entirely qualitative (draw/describe/define/list), with no numeric given data anywhere.

Reference texts: Selley, R.C. & Sonnenberg, S., Elements of Petroleum Geology, 3rd ed., Academic Press (source rocks, migration, traps, carbonate systems, oil sands); Tissot, B.P. & Welte, D.H., Petroleum Formation and Occurrence, 2nd ed., Springer (kerogen typing, maceral groups, catagenesis); Boggs, S. Jr., Petrology of Sedimentary Rocks, 2nd ed., Cambridge (source-rock, deltaic and carbonate lithofacies; sandstone diagenesis); James, N.P. & Jones, B., Origin of Carbonate Sedimentary Rocks, Wiley-Blackwell (carbonate platform/ramp/sabkha facies models); Butler, R.M., Thermal Recovery of Oil and Gas, Prentice Hall, 1991 (SAGD, CSS, oil sands thermal recovery); Green, D.W. & Willhite, G.P., Enhanced Oil Recovery, SPE Textbook Series Vol. 6 (thermal EOR mechanisms); Law, B.E. & Curtis, J.B., “Introduction to Unconventional Petroleum Systems,” AAPG Bulletin 86, 2002 (shale gas, tight gas, coalbed methane); Lee, W.J. & Wattenbarger, R.A., Gas Reservoir Engineering, SPE Textbook Vol. 5 (unconventional gas reservoir characterization).

Section 3, Q3-3: Two methods for developing a bitumen-saturated sandstone reservoir – SAGD and CSS (4 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.

Thermal in-situ recovery: SAGD (well pair) vs. CSS (single well, cyclic) (a) SAGD – paired horizontal wells steam injector (upper) producer (lower, ≈5 m below) expanding steam chamber gravity drainage (b) CSS – single well, cyclic (“huff-and-puff”) heated, pressurized zone 1. Inject steam (weeks) 2. Soak / shut-in (days–weeks) 3. Produce heated bitumen (months) 4. Repeat cycle
(a) SAGD: a steam-injection well drilled directly above a parallel production well (typically ≈5 m separation); steam rises and spreads laterally to form an expanding chamber, and heated, mobilized bitumen drains continuously by gravity to the lower producer. (b) CSS: a single well cyclically injects steam, is shut in to “soak” and conduct heat into the surrounding bitumen, then produces the heated, mobilized oil back through the same wellbore before the cycle repeats.

(a) SAGD (Steam-Assisted Gravity Drainage) uses a vertically paired set of horizontal wells drilled into the pay: an upper injector continuously injects steam, which rises (being less dense than the cold bitumen/water) and spreads laterally, heating bitumen at the chamber margin and reducing its viscosity by several orders of magnitude; the mobilized oil and condensed water then drain continuously, under gravity alone, to the lower producer a few metres below. SAGD gives a smooth, continuous production profile and high ultimate recovery (commonly 50–70% of OOIP) because the steam chamber grows to sweep essentially the whole vertical pay interval, but it requires a thick (>15 m), laterally continuous, relatively clean sand with no major shale barriers to work efficiently.

(b) CSS (Cyclic Steam Stimulation, “huff-and-puff”) uses a single well that alternates between an injection phase (steam pumped into the near-wellbore reservoir for days to weeks), a soak phase (the well is shut in so heat conducts further into the bitumen), and a production phase (the same well flows back the now-mobile, heated bitumen along with condensed steam, aided by the pressure built up during injection) – the cycle is then repeated, with recovery per cycle typically declining as the heated zone around the well cools and the drive pressure depletes. CSS requires only single wells (lower up-front capital than a SAGD well pair) and tolerates thinner or more heterogeneous sands than SAGD, but achieves markedly lower ultimate recovery per well (commonly 20–35% of near-wellbore OOIP, and much less of the total pool) because it heats only a limited radius around each vertical or near-vertical wellbore rather than sweeping a continuous chamber.