RESERVOIR ANALYSIS

1. Interpretation of
Formation Pressure Data

2. Raw Data Table
(With Initial Fluid Interpretation)

3. Step 1: Plot the Data
• Pressure on the x-axis
• Subsea (vertical) depth
on the y-axis

4. Step 2: Initial Visual Interpretation
Initial Interpretation;
• 3 Fluids
• GOC near 10600 Ft SS
• OWC (FWL) near 10700 Ft SS
• Unknown fluid at 9626 Ft SS
– Not in pressure communication
w/ underlying reservoirs
?
Gas
Oil
Water

5. Step 3: Initial Quantitative Interpretation
Remarks;
• Gas gradient look realistic
• ?Oil gradient looks too low
• Exclude data from 9626 Ft SS
Gas
Oil

6. Step 4: Detailed Look at GOC
Remarks;
• Initial interpretation has oil zone
data points above the gas-oil
contact
Apparent GOC

7. Step 5: Revised Interpretation of Gas-Oil System
Remarks;
• Oil gradient (density) more realistic that
initial interpretation

8. Detail of Revised Interpretation
Remarks;
• Realistic oil gradient
But;
• Only 2 data points in ?oil column,
• Lowest data point at 10673.8 ft SS has
very low drawdown mobility (k/u). The
resultant apparent pressure and gradient
are therefore uncertain.
• Apparent gradient should be checked for
conformance with other field data
GOC 10645

9. Feasible – but high water gradient
Step 6: Check for Realistic Data
Remarks;
• Pressure gradient between bottom 2
points is not realistic – far too high
• A feasible but very high density water
gradient projects into the hydrocarbon
zone,
• This is not possible if the fluids are in
pressure communication

10. Step 7: Is the Interpretation Realistic
• Are the fluid pressure gradients realistic and consistent with the
interpreted fluid
• Utilize offset well and regional fluid pressure gradient data
• Be prepared to eliminate data from the interpretation;
− Remove data points with low drawdown mobility to improve
consistency of interpretation,
− Eliminate data if there is an apparent pressure discontinuity (data at
9626 ft SS, for example)
• Sometimes data cannot be used to determine fluid contacts. For
example, the gradient in the assumed water zone is unrealistic. Also, a
realistic water gradient plots into a known hydrocarbon zone.
• Be prepared to change the interpretation as more data becomes available.
For our example no wireline log data or fluid sample data was available.

11. Table for Fluid Pressure Gradient Conversion