Assignment2-Serhat Ezer

Petroleum Geology- GEOL 4190/5190 Assignment 2 (Drilling and Completion; Formation Evaluation; Gravity, magnetic, and electromagnetic methods of geophysical exploration) Note: These are multiple choice questions. If it is explicitly specified “choose all that are correct”, there are multiple answers to that question. Else, there is only a single answer to the question, and you will receive zero credit if you choose more than one answer even if one of the choices is the correct answer. Please identify your answer(s) by highlighting with a color or by using a different font color. 1. What are the fundamental drawbacks of using cable-tool drilling in oil and gas exploration? Choose all that are correct. a. Does not work in an open-hole. b. c. Works only in open-hole d. Unsafe, may cause blow-outs. e. Maximum drilling depth is severely limited by mechanical constraints. f. Rate of penetration is too slow. 2. What are the primary functions of the drilling mud? Choose all that are correct a. Borehole stability and safety. b. Prohibit the casing from corroding. c. Keep the drill-bit cool. d. Remove cavings from the borehole wall. e. Increase resistivity of the borehole. 3. In rotary-drilling, an ordinary drill-bit is sometimes replaced by a core-barrel to collect rock samples. What is the primary reason for collecting rock samples using the core-barrel? a. Increase drilling speed (i.e., increase the rate of penetration). b. Reduce drilling speed. c. Conduct laboratory analysis using the samples. d. None of the above. 4. Out of the list below, which one is a radioactive log? a. Spontaneous Potential (SP). b. Induction. c. d. Density. e. Sonic 5. Recall Archie’s formula where the formation factor F is given as F = a φ m , where a and m are constants and φ is the porosity. In a sandstone formation in an area, F has been estimated to be 17 using the resistivity log. It is also estimated that a =0.81 and m =2.2 for the sandstone. Then what is the porosity of the formation? Mark the closest answer. a. 0.15 b. 0.35 c. 0.60 d. 0.25 e. 0.07

6. The Figure above shows SP, shallow-resistivity and deep-resistivity logs run over a sandstone. The deflection of the SP log from the shale baseline indicates the entire sandstone interval is porous and permeable. Additionally, an inspection of the shallow and deep resistivity log indicates an upper productive interval and a lower water zone. Also shown that the deep resistivity readings in the upper productive interval and the lower water zone are respectively 750 and 15 Ω.m. Considering that the water zone is 100% water saturated and using the simple formula for water saturation S w = √ R 0 R t , as we discussed in the class, what is the hydrocarbon saturation S hc for the upper productive interval? Please choose the closest answer. a. 0.7 b. 0.95 c. 0.86 d. 0.5 e. 0.6 7. A shallow resistivity log measures the resistivity of the flushed zone where the formation fluid is completely flushed out by the mud filtrate. A deep resistivity log on the other hand measures the resistivity of the uninvaded zone where the original formation fluids are in place. If there is a difference in the reading between the deep and shallow resistivity logs, it usually indicates a. Limestone. b. Sandstone. c. Dolomite. d. Shale. e. A porous and permeable formation. 8. Which of the following logging tools is sensitive to the hydrogen concentration in the formation and gives reliable liquid filled porosities in non-shale rocks? a. Neutron log. b. Gamma-ray log. c. Sonic log. d. Resistivity log. 9. The density reading over a sandstone formation is 2.3 g/cm 3 . Considering that the rock matrix of the sandstone formation is quartz with density 2.65 g/cm 3 and the formation is 100% brine-

14. The Figure above shows the result of the Alford rotation of the dipole shear log from the acquisition directions along the X- and Y coordinates (XX, XY, YX, YY) to the directions F and S where the energy on the cross-components (FS and SF) are minimized. If the log is run over a suspected fractured interval, what do you think would be the direction parallel to the fractures? Hint- along the direction parallel to the fractures, the S waves travel slower than the direction perpendicular to the fractures . a. X b. Y c. F d. S 15. Formation porosity can be estimated from which of the following logs? Choose all that are correct. a. Resistivity b. Gamma-ray c. Neutron d. Sonic e. Density 16. What is the most effective geophysical method for petroleum exploration? a. Gravity b. Seismic c. Electromagnetic d. Magnetic 17. According to the Google search results, Laramie, WY is located at latitude 41.3114°N and longitude 105.5911°W. Using the international gravity formula of Moritz (1980), what is the gravity value for Laramie, WY in mgal? Mark the closest answer. a. 981592.2907 b. 982606.3568

c. 980286.2405 d. 980122.3142 18. The international gravity formula of Moritz (1980) is however the expected value of gravity at a given latitude, measured at the sea-level. Per Google search, Laramie WY is 7165 feet (2183.892 meters) above the sea-level. So, the free-air correction must be subtracted from and the Bouguer correction must be added to the gravity value at the sea-level to find the expected value of gravity for a location. Thus, using the sea-level gravity value, estimated from question 17 and assuming an average density of 2.1 g/cm 3 , if you take a gravimeter and measure the gravity field in Laramie, what background value of gravity in mgals would you expect? Mark the closest answer. a. 979038.1244 b. 982321.7659 c. 981534.3567 d. 981899.7562 19. Gravity method is useful for delineating (choose all that are correct) a. Structural traps b. Stratigraphic traps c. Hydrocarbon accumulations d. Diapiric (salt dome) traps 20. What rock property does magnetic method measure? a. Acoustic velocity b. Magnetic susceptibility c. Resistivity d. Density 21. What kind of hydrocarbon traps can be delineated using the magnetic methods? a. Stratigraphic traps b. Structural traps c. Diapiric traps d. Hydrodynamic traps 22. Magnetic methods require measuring the background magnetic field at a base station as a function of time. What is the reason for this? a. To correct for the wild fluctuations in the earth’s magnetic field caused by the magnetic storms or the sun-spot activities. b. Unlike the gravity field, earth’s background magnetic field is not constant but time- variant ranging from hundreds of years to about a second. Measuring this time-varying fluctuation allows correcting the observed data. c. The magnetic field is measured at the base station because the average of the base station reading and the reading at the field location is the true magnetic field. d. None of the above. 23. Which one out of the following rocks is expected to give the highest magnetic anomaly? a. Igneous basement rock b. Sandstone c. Shale d. Limestone e. Dolomite 24. What rock property does the electromagnetic (EM) method provide? a. Thermal conductivity b. Density