HOMEWORK 1, DUE JANUARY 29TH 2015

SUBMISSION TIME: AT THE BEGINNING OF CLASS. TURNING IN A LATE SUBMISSION

BEYOND 8.45 AM ON JANUARY 29TH 2015 WILL RESULT IN A LOSSS OF 10% OF YOUR

GRADE FOR EVERY DAY THAT YOU ARE LATE.

You are encouraged to discuss the homework problems with your colleagues, or to use any

other source of information to guide you. Please, however, turn in your own work.

Collaboration in any form except as specified above will be strictly penalized.

Problem 1.

10900

10800

10700

001) BONANZA 1

50150 us/fDT

-0.150.45CNLLC

2.951.95RHOC

2000.2MLLCF

2000.2SNC

2000.2ILDC

166ACAL

40-160 MVSPC

1500GRC

This problem will illustrate the typical workflow for log analysis. You may want to export

the log curve values to a spreadsheet application. Assume that the logging tools have an

average resolution of 10 feet (although typical tool resolution is about 1-2 feet). Therefore

your spreadsheet should have 10-feet-averaged values of the reported log values.

Curve Mnenomics:

MLLCF: Shallow resisitivity

SNC: Medium resistivity

ILDC: Deep resistivity

GRC: Gamma ray

CNLLC: Neutron porosity

RHOC: Density

DT: Sonic travel time

You may assume that the neutron log is reading the correct values of porosity in clean,

water-bearing layers.

a. Identify clean and shaly layers. Indicate these layers on your log. Comment on the

permeability of the formation in these layers using all available data.

b. Identify water-bearing and hydrocarbon bearing layers in the log. Do this without

any explicit calculations using Archie’s equation – use only the log responses

qualitatively (gamma ray, resisitivity profiles etc)

c. Use the clean, water-bearing layer information to obtain a value for the formation

water resisitivity, Rw. You may use the deep resisitivity curve as a substitute for the

uninvaded formation resistivity Rt. Do this using two different methods:

a. Use the Rwa method. This is the method we discussed in class. Chose a few

points in the log in the clean, water-bearing layers and calculate Rw as an

average of the previously obtained values.

b. Use the Pickett plot technique. This is a powerful technique for Rw

computation and an example is provided in your lecture slides. On a log-log

chart, plot the porosity (on the y-axis) versus formation resistivity (on the x-

axis). Draw a line passing through the points with a 100% water saturation,

extend the line to intersect the x-axis at a porosity value of 100%. Obtain the

value of formation water resistivity from this chart. See SPE 1446 by Pickett,

G.R. for more information.

d. Use the same method specified above to calculate the mud filtrate resistivity, Rmf.

You may use the shallow resistivity as a proxy for the invaded zone resistivity, Rxo.

e. Compute the density porosity and plot it on a log for a

a. Limestone matrix (2.71 g/cc)

b. Sandstone matrix (2.65 g/cc)

c. Dolomite matrix (2.87 g/cc)

d. Assuming there are no lithology effects affecting the neutron log response

(i.e. the neutron log is reading the correct porosity in a 100% water-

saturated clean formation), what is your assessment of the lithology of the

formation. (Hint: If you chose the correct matrix density, the density porosity

and the neutron porosity will overlay in a clean, water-bearing layer)

f. Compute and plot the water-saturation on your log. Indicate clearly the shale

sections, where this computation is not meaningful.

g. The sonic log is also a very useful tool for porosity estimation. The curve DT

represents the travel-time of sound waves in the formation. So at a depth of 10870

feet, it takes sound 100 micro-seconds to travel one foot of the formation. The sonic

travel-time is strongly dependant on porosity and the rock matrix. The formula that

relates sonic travel-time to the rock matrix travel-time and fluid travel-time is

similar to that of the bulk density formula.

Compute the sonic porosity and plot it on a log for a

a. Limestone matrix (47.5 us/ft)

b. Sandstone matrix (55.5 us/ft)

c. Dolomite matrix (43.5 us/ft)

d. The speed of sound in water is 1500 m/s.

e. Assuming there are no lithology effects affecting the neutron log response

(i.e. the neutron log is reading the correct porosity in a 100% water-

saturated clean formation), what is your assessment of the lithology of the

t log= tma (1 − φ ) + t f φ

formation. (Hint: If you chose the correct matrix, the sonic porosity and the

neutron porosity will overlay in a clean, water-bearing layer)

f. Use the sonic porosity to compute the water-saturations in the formation.