Dept. of Petroleum Eng. and Appl. Geophysics Page 1 of 3 TPG5120 Petrophysics Basic Course. Hand in exercise answer in shelves in 2nd floor.

Page 1 H. Langeland, Norwegian Univ. of Science and Technology, NTNU. 10/6/2004

Exercise 5: TPG5120 Petrophysics Basic Course, Well 33/9-1 Statfjord

Using Pickett plot to find Sw, m and aRw.

The theory of Pickett plotting is given in the book “Introduction to Wireline Log Analysis” by Atlas Wireline Services on pages 240 - 243. You should keep in mind that the procedure is based on Archies equations, and that means a relatively clean formation: Vcl is small.

In earlier exercises we used Humbles formula with a = 0.62 and m = 2.15. These parameters are empirical and may vary. If your data permits you may be able to find estimates of m, and aRw, and at the same time find water saturation, Sw .

The procedure is based on analysis of a clean water bearing part of the reservoir where you will look for variations in φ and Rt and where you know that Sw = 1. Zones of constant Sw will plot along lines in a log-log plot of φ versus Rt. You will search for zones in the water bearing part of the reservoir that gives spread in φ and Rt large enough to be able to draw a line through the points. Thus you will search for zones that will give you enough separation of the plotted points. If the spread of points is not large enough to fit a line, you may have to assume known either aRw or m.

As a porosity log you may use ρb, φn or ∆t. However, in this exercise you are going to use the neutron log where you will plot φN along the y-axis. Plot values from the water bearing part of the reservoir. Fit, if possible, a line of Sw = 1 to the points and calculate m and aRw.

If you are not able to fit a line to the points, you have to assume that aRw or m is known. You will then be able to establish the water point (where aRw = Rt and φN = 1 ) or the slope of the curve -1/m.

After you have fitted the water line, you are asked to draw lines for other saturations. Read out the saturations of your zones from the plot and enter the results into the form. Compare with saturation values from the other methods. Use the attached log-log plot paper.

Using Hingle plot to find Rmf and Sxo. Use the attached Hingle diagram paper to plot log data to establish the Rmf resistivity. Does the found

value fit with the previously calculated value of Rmf. As a porosity log you may use the density porosity calculated from the density log. In the water zones use RHOma = 2.68, and in other zones use 2.65. You may want to use a RHOfl different from 1 in the hydrocarbon zones in your calculations of porosity.

Use the plot to find Sxo of your zones in the well.

Hand in exercises by Monday, Oct. 18.

Dept. of Petroleum Eng. and Appl. Geophysics Page 2 of 3 TPG5120 Petrophysics Basic Course. Hand in exercise answer in shelves in 2nd floor.

Page 2 H. Langeland, Norwegian Univ. of Science and Technology, NTNU. 10/6/2004

Dept. of Petroleum Eng. and Appl. Geophysics Page 3 of 3 TPG5120 Petrophysics Basic Course. Hand in exercise answer in shelves in 2nd floor.

Page 3 H. Langeland, Norwegian Univ. of Science and Technology, NTNU. 10/6/2004