This document discusses various methods for predicting the performance of oil and gas reservoirs. It begins with defining key terms like undersaturated reservoirs, gas-oil ratio (GOR), and pore volume. It then describes different drive mechanisms like rock and liquid expansion, gas cap drive, water drive, and combination drives. The document outlines several methods for performance prediction based on material balance concepts and numerical approaches. It provides step-by-step explanations of methods like Muskat's prediction algorithm and the Fetkovich method for vertical wells. Finally, it lists references for further information on reservoir engineering topics.

1. PERFORMANCE PREDICTION
OF A
PAY ZONE
By
Syed Nawaz
M.Tech Petroleum Exploration and Production
Delta Studies Institute, AU

2. CONTENT
• Introduction
• Basic Terms for topic
• Derive Mechanism
• Types of methods for prediction based on material balance concept
• Types of methods for prediction based on numerical approach
• References

3. OBJECTIVES
• Upon completion of this ppt, we should atleast be able to:
• Understand the concept of reservoir performance prediction
• Describe the various prediction methods
• Derive instantaneous GOR
• Describe the step by step approach of one prediction method
• Perform prediction calculation if you want
• Methods based on pressure and flow rate

4. TERMS
• Undersaturated reservoir
• GOR: When oil is brought to surface conditions it is usual for some natural gas to come out of solution.
The gas/oil ratio (GOR) is the ratio of the volume of gas that comes out of solution, to the volume of oil
at standard conditions. In reservoir simulation gas oil ratio is usually abbreviated Rs
• Bo
• Bg
• Bt
• So,Sg,Sw
• Krg, Kro, Krw, Keo, Keg, Kew
• Compressibility

5. DERIVE MECHANISM
• Rock and Liquid Expansion
• Depletion Drive Mechanism
• Gravity Drainage
• Water Drive Mechanism
• Combination Drive Mechanism

6. ROCK AND LIQUID EXPANSION
• When reservoir pressure decline below bubble point pressure then rock expansion of
rock occurs and in same way expansion of the fluid and reduction in the pore volume
occur, the crude oil and water will be forced out of the pore space to the wellbore. The oil
reservoir under this driving mechanism is characterized by a low and constant producing
gas oil ratio that is equal to the gas solubility at the bubble point pressure.
• It only helps to recover 1%to 5% of total recovery

7. SOLUTION GAS DRIVE
• When the reservoir pressure declines below the bubble point pressure due to oil production,
dissolved gas starts to come out of solution. The free gas is not produced until critical gas
saturation is developed. Depletion below the bubble point causes the gas phase to increase
rapidly in the reservoir and the principal source of energy is due of gas liberation from the
crude oil and the subsequent expansion of the solution gas as the reservoir pressure is
reduced.
• The low recovery from this type of reservoirs suggests that large quantities of oil remain in
the reservoir and therefore depletion-drive reservoirs are considered the best candidates for
secondary recovery applications.
• Oil recovery is 10%-25%

8. GAS CAP DRIVE MECHANISM
• When initial reservoir pressure and temperature are within the 2 phase region,
reservoirs with gas caps are encountered and gas being lighter than oil, it rises above oil
zone due to gravity segregation. As the reservoir pressure decline with production, the
gas cap expands, resulting in gas cap drive.
• Ultimate recovery is 15%-35%

9. WATER DRIVE MECHANISM
• When an oil or gas reservoir is in communication with a surrounding active aquifer,
production from the reservoir results in a pressure drop between the reservoir and the
aquifer. This allow influx of water into the reservoir.
• A producing reservoir is referred to as bottom water drive or edge water drive reservoir,
providing energy for production.
• The aquifer may be so large compared to the reservoir they adjoin as to appear infinite for all
practical purposes and they may range down to those so small as to be negligible in their
effects on the reservoir performance.
• Ultimate recovery is 30%-80%.
• Note : as the reservoir heterogeneity increases the recovery of the reservoir decreases.

10. THE GRAVITY DRAINAGE DRIVE
MECHANISM
• The mechanism of gravity drainage occurs in petroleum reservoirs as a result of
differences in densities of the reservoir fluids.
• The fluids in petroleum reservoirs have all been subjected to the forces of gravity as
evidenced by the relative positions of the fluids i.e., gas on top, oil underlying the gas,
and water underlying oil.
• Based on research on various well around the world the recovery is upto 80%

11. THE COMBINATION DRIVE MECHANISM
• The most common type of drive encountered is combination drive
• Every drive mechanism is depends on the following parameters performance
• Reservoir pressure
• Water production
• Gas oil ratio
• Vertical permeability and relative permeability
• Oil viscosity
• Dip angle

12. PREDICTION METHODS BASED ON
MATERIAL BALANCE
• Tracy method
• Muskat method
• Tarner method
• Schilthuis method
All the techniques used to predict the future performance of a reservoir are conditioned
reservoir pressure should less than the bubble point pressure
The prediction of reservoir when its pressure is greater than the bubble point pressure is
determine by equations presented in Craft and Hawkins 1991, L.P.Dake 1978, Tarek Ahmed
2010, Cole 1969, Cosse 1993, Economides et.al 1994, and Hawkins 1955

13. THE MATERIAL BALANCE EQUATION FOR
ABOVE AND BELOW BUBBLE POINT PRESSURE

14. MUSKAT’S PREDICTION ALGORITHM
• At any given pressure this method is valid,
• Parameters estimated during this test is
• Estimating Bg, Bo, Rs behavior with respect to change in pressure
• Change in saturation at average reservoir pressure and at any pressure,
• Steps to be followed to predict the performance
• 1- Obtain relative permeability data at corresponding saturation values and then make a plot
of Krg/Kro versus saturation.
• 2- Make a plot of fluid properties {Rs, Bo and (1/Bg)} versus pressure and determine the slope of
each plot at selected pressures, i.e., dBo/dp, dRs/dp, and d(1/Bg)/dp.

15. • 3- Calculate the pressure dependent terms X(p), Y(p), and Z(p) that correspond to the
selected pressures in Step 2.

16. • 4- Plot the pressure dependent terms as a function of pressure, as illustrated in the figure
below.

17. • 5- Graphically determine the values of X(p), Y(p), and Z(p) that correspond to the pressure P.
• 6- Solve for (ΔSo /ΔP) by using the oil saturation (So)i 1 at the beginning of the pressure
drop interval Pi 1.

18. • 7-Determine the oil saturation So at the average reservoir pressure P, from
• 8- Using the So from Step 7 and the pressure P, recalculate (ΔSo/ΔP)

19. • 9- Calculate the average value for (ΔSo/ΔP) from the two values obtained in Steps 6 and
8.
• 10- Using ΔSo/ΔP Avg, solve for the oil saturation So from

20. • 11- Calculate gas saturation (Sg)i by:
•
• 12- Using the saturation equation given below

21. • 12.A- To solve for the cumulative oil production.
• 13- Calculate krg/kro at the selected pressure, Pi
• 14- Calculate the instantaneous GOR at the selected pressure, Pi

22. • 14- Calculate the instantaneous GOR at the selected pressure, Pi
• 15- Calculate the average GOR

23. • 16-Calculate the cumulative gas production by using Np from step 12 and step 15
• 17- Repeat Steps 5 through 13 for all pressure drops of interest.
• IF YOU ARE INTERESTED THEN WILL A NUMERICAL PROBLEM..?....

24. QUESTION ?
• Given a saturated oil reservoir located at Amassoma oil field in Bayelsa State with no
gas cap; whose initial pressure is 3620 psia and reservoir temperature of 220 F. The
initial (connate) water saturation is 0.195 and from volumetric analysis, the STOIIP was
estimate as 45 MMSTB. There is no aquifer influx. The PVT data is given in the table
below.
• In this field, there is no relative permeability data available. Hence, the correlation below
is used to generate the relative permeability curve.
• Calculate the cumulative oil and gas production at 3335 psia using the Muskat method

35. FOR VERTICAL AND HORIZONTAL WELLS
PREDICTION METHODS ARE
• VETICAL WELL PREDICTION METHODS
• Vogel’s method
• Wiggin’s method
• Standing’s method
• Fetkovich method
• HORIZONTAL WELL PREDICTION METHODS
• Borisov’s method
• The Giger Reiss method
• Joshi’s method
• The Renard-Dupuy method

36. VERTICAL WELL FETKOVICH METHOD

41. HORIZONTAL METHOD

45. REFERENCES
• Reservoir Engineering hand book
• Funmentals of Reservoir Rock
• Reservoir engineering by selvester
• Syed Nawaz, Student of Andhra Univeris Free Lance NDT Inspector
• SPE
• Rigzone
• Reservoir Geomechanic Course offered by MARK ZUBACK

46. ANY QUERIES?

47. THANKS??