The petroleum system
What are properties of cap rock
No porosity no permeability
Why might an operator choose a directional well instead of a vertical well?
Reach multiple targets, reduce surface footprint, drill beneath obstacles.
Which logging measurement is most commonly used to distinguish shale from clean sand?
Gamma Ray
Drilling a new infill well is classified as?
CAPEX
What is the purpose of kelly bushing
Transfer Rotation to the Drill String
Name the 5 key elements in a petroleum system
Source rock, migration pathway, reservoir rock, seal, trap.
Which comes first: running casing or cementing casing?
Casing
A zone has high resistivity and low water saturation. What fluid is likely present?
Hydrocarbons
What is the very first step of economic evaluation ?
Estimating reserves and forecasting production
A well is being drilled below a city where surface access is restricted. Which well trajectory would most likely be selected?
Directional (or highly deviated) well.
A geological structure contains excellent reservoir rock and seal but no mature source rock nearby. What critical risk remains?
A formation pressure is higher than the hydrostatic pressure in the well. What risk immediately develops?
Kick / influx of formation fluids.
Why is resistivity alone not enough to confirm hydrocarbons?
It must be integrated with porosity and lithology information
A project has enormous reserves but requires extremely high development costs. What economic question must be answered?
Whether the reserves can be produced profitably.
What is the difference between TVD, MD and TVDSS
MD: The actual length of the wellbore measured along the drilling path from surface to the point of interest.
TVD:The vertical distance from a reference point (usually rotary table, kelly bushing, or rig floor) straight down to the point of interest.
TVDSS:Vertical depth measured relative to mean sea level (MSL) instead of the rig floor or ground elevation.
Which petroleum system element directly prevents hydrocarbons from escaping after accumulation?
Seal (cap rock)
What is the primary purpose of drilling mud before considering hole cleaning?
Maintaining well control through hydrostatic pressure
What is the primary advantage of LWD over wireline?
Data acquired while drilling, allowing faster decisions
which estimate has the largest reserves? P10, P50 or P90
P10
What are the 4 types of pressures present while drilling
Pore pressure, fracture pressure, hydrostatic pressure, overburden pressure
You discover a sandstone with 25% porosity but no effective seal. Is it likely to be a commercial accumulation? Why?
No, hydrocarbons would likely leak and fail to accumulate.
An engineer increases mud weight significantly to control a kick. What new drilling problem might occur?
Lost circulation/ formation fracturing
A reservoir shows high porosity but very low resistivity. What fluid is most likely occupying the pore space?
A project has enormous reserves but requires extremely high development costs. What economic question must be answered?
Whether the reserves can be produced profitably.
You are drilling toward a reservoir with a formation pressure of 5,000 psi.
Option A: Well pressure = 4,800 psi
Option B: Well pressure = 5,200 psi
Which option is safer and why?
Option B because well pressure exceeds formation pressure and maintains primary well control. Option A risks a kick.