Project Topic: Decline Curve Analysis for
Horizontal Wells in the Niger Delta
Student Name: George, Felicia Apiafi
Supervisor: Prof. D. T. Numbere
Brief description: Horizontal wells have become common in the Niger Delta. The primary objective of this project is to analyze the production from such wells to establish if they follow the conventional decline modes such as exponential, harmonic and hyperbolic.
If they do, then the future
performance of such wells can be predicted using the appropriate decline mode
assuming that the factors which affected the past production trend will
continue into the future.
Data needed:
1.
Oil production rate as a function of time. The time can
be in days, or months, or even years.
2.
Oil production rate as a function of cumulative
production.
|
Time (days or months or years) |
Oil production rate |
Cumulative oil production |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Procedure:
(1)
Check whether exponential decline is applicable.
Therefore, make semi-log plot of rate (log scale) versus time (regular scale).
If the plot gives a straight line, then exponential decline applies. In that
case,
slope
= 
and intercept = 
.
Log Rate Log q Time, t
The
flow rate at any future time t can be calculated using 
The
cumulative recovery at any future time (t) when the flow rate drops to q can be
obtained as:
Very
often, the semi-log rate versus time plot does not give a clearly defined
straight line. In such situations, a production rate versus cumulative oil
production plot on regular Cartesian paper can be made. If the decline data is
exponential, this plot should give a straight line with a slope = -D.
Having
obtained D, the flow rate at any value of cumulative recovery is: 
Harmonic
decline
(2)
Check whether harmonic decline applies by making a semi-log plot of flow rate q
versus cumulative production Np . If the plot gives a straight line,
then the slope = 
and the intercept on the
y-axis = log qi.
Np or Gp
Having
obtained D and qi, then the rate at any future time can be
calculated by the equation 
The
cumulative production at any future tme can be calculated using the equation:
Do not worry about Hyperbolic decline for now.
EXAMPLE
What follows below is an example calculation. You should first make sure that you can reproduce my results. Then using time, rate and cumulative production data from Shell analyze them for the many wells or reservoirs given.
The production data below shows an example of data to be analyzed. It is desired to determine the type of decline. That is whether
a)
Exponential decline, or
b) Harmonic
decline
After that, predict the production rate from year 6 to year
15.
The table below shows the available data. The column labelled "0" is the time in days(n ie 180, 360, ....3600). The column labelled "1" is the cumulative barrels of oil production in thousands. The last column is the oil production rate in bbls/day.
Solution:
Exponential decline analysis
The semi-log plot of rate versus time gives the graph below. A straight line has been fitted to the data.
The slope of the straight line is: -1.265*10-4
Therefore the value of D = (2.303* -1.265*10-4 ) = 2.913*10-4
The intercept is qi = 371.11 bbls/day
The flow rate prediction for years 6 to 15 are:
Checking with the rate –cumulative plot gives the graph below:
The slope of the straight line is: -3.035*10-4
Therefore the value of D = 3.035*10-4
The intercept = qi = 379 bbls/day
The flow rate prediction for years 6 to 15 are:
Harmonic decline
The semi-log plot of rate versus cumulative production is shown below. It is clear that the plot does not give a straight line so the data does not indicate harmonic decline.