PEC EPE Petro-Gas common mistakes
PEC EPE Petro-Gas · Understand the traps and how to avoid them.
In material-balance questions, assumes volumetric OOIP and ignores aquifer influx and connate-water/rock compressibility whenever pressure declines, even when the pressure history flattens.
Candidates memorize the simplest material-balance form and do not first identify the drive mechanism from pressure and water-production trends, so they force a straight-line plot that should curve.
What to do instead
Classify the drive from pressure and water-production trends first, then use Havlena-Odeh or the full material balance with water-influx and compressibility terms; test sensitivity by plotting F versus Et and checking linearity.
Calculates formation pressure from SIDPP alone or uses SIDPP directly as the kill-mud increment without adding hydrostatic head and checking the casing shoe.
Surface pressure is confused with bottomhole pressure, and the candidate rushes into the kill-mud formula without writing the pressure balance.
What to do instead
Write BHP = SIDPP + hydrostatic drillpipe pressure; calculate kill mud weight as current MW + SIDPP/(0.052 × TVD); then verify the shoe pressure remains below MAASP before recommending the kill sheet.
Uses a constant productivity index to predict rate at a flowing bottomhole pressure below bubble point.
The straight-line PI equation is the first IPR model learned, and candidates apply it without checking whether the reservoir pressure and flowing pressure keep the well above saturation pressure.
What to do instead
Compare flowing pressure with bubble point; if below it, use Vogel or a composite IPR, calculate qmax from a valid test point, and state that PI is valid only for single-phase liquid flow.
Uses ideal-gas density or formation volume factor at high pressure and temperature without evaluating the Z-factor.
The ideal-gas law is simple and unit-consistent, so candidates skip the real-gas correction even when pressure is high and gas composition is rich.
What to do instead
Calculate Z with Standing-Katz or an equation of state, then use real-gas relations for density and Bg; sanity-check the result against gas composition and measured PVT data.
Sizes a gas transmission line with a single-phase gas pressure-drop equation when the stream is a rich gas-condensate and liquid dropout is expected.
The candidate treats the line as dry gas because the sales specification is gas, ignoring the phase envelope and operating temperature-pressure path.
What to do instead
Construct the phase envelope, estimate liquid holdup and slugging potential, use a multiphase flow method or validated correlation, and check the design against turndown and pigging scenarios.
Treats a high-amplitude seismic bright spot as a direct hydrocarbon indicator without checking AVO class, tuning effects, or lithology.
Bright spots are memorable exploration shortcuts, and candidates skip the rock-physics and well-tie checks that distinguish gas sand from wet sand or coal.
What to do instead
Tie the anomaly to wells, model AVO responses for wet and gas-bearing cases, examine intercept-gradient crossplots, and state the alternative non-hydrocarbon explanations before interpreting pay.
Applies Archie's equation with m = n = 2 in a shaly sand or conductive-mineral carbonate and reports water saturation without clay correction.
Archie is the default formula in basic log-analysis training, and candidates do not check whether the formation satisfies Archie's clean-sand assumptions.
What to do instead
Estimate shale volume from GR and neutron-density, apply Waxman-Smits or dual-water where clay conduction matters, calibrate to core or SCAL data, and flag intervals where Archie is invalid.
Discounts nominal escalated cash flows with a real discount rate, or mixes real costs with nominal prices, when calculating NPV.
Discount rates are often quoted without an inflation basis, and candidates do not reconcile the cash-flow basis with the rate basis.
What to do instead
State whether each input is real or nominal; convert consistently using (1 + nominal) = (1 + real)(1 + inflation); apply the same timing convention, such as mid-year, to all cash flows.
Adds expected monetary values of individual prospects to rank a portfolio without considering correlated geological risk or shared infrastructure.
EMV is treated as additive and independent, so candidates sum prospect values even when the same source rock, seal, or play chance affects all of them.
What to do instead
Use a decision tree or Monte Carlo model with common risk factors, report P10/P50/P90 outcomes, and rank by risk-adjusted value rather than by simple EMV addition.
Closes a HAZOP or audit action on verbal assurance alone because the schedule is tight, without documented evidence or independent verification.
Schedule pressure and authority gradient push candidates to accept reassurance instead of evidence, and they do not record the residual risk.
What to do instead
Require documented verification, assign an independent checker, escalate unresolved high-consequence risks, and record dissent and management-of-change decisions in the action log.