3. Page 3
Multidisciplinary approach
Petrophysics Saturation
Reservoir
Engineeri
ng
Geolog
y
(Maps)
Geophysics
(Seismic)
Fluid
property
function
Production
history
Well Testing
Drive
mechanism
Reservoir Model
Reservoir Development Plan
Prediction of Reservoir Performance
31. Page 31
Introduction to Reservoir
Engineering
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Editor's Notes
RE’s use data from a range of sources
Petrophysics – electric log interpretations
Core data recovered from the reservoir
Well tests – flow the well into a separator and flare it while measuring the bottomhole pressure (at the bottom of the well)
Measurement of the properties of the rocks.
When we do a well test on an exploration or appraisal well, we need to flare the gas/oil since we have no pipeline or tanker export route.
Discuss the range of fluids from dry gas to essentially coal, and various shades in between.
Oils are various colours – Miller East example
Should we show a slide of oil sample colours?
Darcy equation – liked to most of our equations
Based on experiemnts in the Paris sewers! No really Jane Austen!
Psi – pounds per square inch
Most reservoirs pressures are at hydrostatic pressure
This essentially a column of seawater from the surface of the sea to the hydrocarbon – water contact in the reservoir.
There are reservoirs which we can HPHT – high pressure-high temperature. These have pressure and/or temperatures which exceed most reservoirs.
Usually the reservoir rock, supports the weight of the overburden rock above it, however in some circumstances the reservoir rock compresses due to the ovverburden and the reservoir fluid has to support some of the weight.
As an oil reservoir depletes in pressure, gas will come out of solution (like opening a can of coca cola) and bubble out of the oil. It will be a bit more lively than coca cola though.
Bubble Point is the pressure at which the first bubble of gas comes out of the liquid oil.
As gas bubbles out of the oil, it will shrink – or reduce in volume. A bit like boiling a kettle dry.
Then once all of the gas has bubbled out, which is what we do in a separation system on an oil platform using separators (pressurised tanks), we are left with what we call Stock Tank Oil.
For gas, it is kind of the opposite way round.
Dew Point is defined as the pressure at which the first droplet of oil condenses out of the gas. This is similar to how water vapour condenses on a mirror in the bathroom.
As the pressure drop more, then so a larger volume of condensate comes out of the gas.
Permeability is measured in samples of core recovered from the well by blowing gas through it.
Permeability can be calculated by measuring pressures in a well test when it is flowed.
Initial oil saturation could be 75%, and residual oil saturation 35%, so therefore 47% of the oil would be left behind.
Migration of oil into a reservoir over a very long time.
Water being pumped into a reservoir to flush out the oil.
In the olden days, the pressure was allowed to drop since no water was injected. Gas then came out of solution.
Gas travels much quicker than oil in the reservoir – maybe 100 times faster, so after a short time, the wells would gas out. In the olden days nobody was bothered about gas, so it was just either flared, or vented. Recovery factors were low such as 10-15%.
Onshore USA, CO2 is frequently used for tertiary recovery. An additional 5 to 15% of reserves can be recovered. Offshore such as in the UK North Sea it is much more expensive to get CO2 offshore.
It is not impossible to do, but somebody needs to pay for the pipeline!
There is a term FID – Final Investment Decision – at which the decision is made by a company to spend billions of pounds to develop an oil field.
GIGO – Garbage in – garbage out
A model is only as good as the data that is put into it
It will always be an approximation.
If you imagine a very large bed sheet over a huge feast on a kitchen table, and a tiny pin prick in the sheet samples an apple. That is what a well measures. How will the driller know what is on the rest of the table?
