ENCH 617 – Advanced Production Operations – Midterm Exam, November 1, 2006 Name______________________________ Student ID #_________________________ Duration – 90 minutes Closed book, closed notes, regular mathematical calculators only TOTAL MARKS Multiple Choice – 25 x 2 marks each = 50 possible Marks ______________ Short Answer – 20 possible marks _______________ Computational – 30 possible marks _______________ (Bonus question 3 marks – optional) PART 1 – MULTIPLE CHOICE PICK THE BEST ANSWER TO EACH QUESTION – 2 MARK PER MULTIPLE CHOICE QUESTION, NO DEDUCTIONS FOR WRONG ANSWERS 1. A fluid system whose apparent viscosity decreases as shear rate increases is known as a; a. Newtonian Fluid b. Thixotropic Fluid c. Rheopectic Fluid d. Bingham Plastic Fluid 2. The Gas Formation Volume Factor ‘Bg' can be defined as; a. The volume of a unit volume gas at standard conditions of temperature and pressure b. The volume a unit volume of gas at reservoir conditions of temperature and pressure c. The ratio of the volume of a given amount of gas at standard temperature and pressure divided by the volume of the same amount of gas at reservoir temperature and pressure. d. The ratio of the volume of a given amount of gas at reservoir temperature and pressure divided by the volume of the same amount of gas at standard temperature and pressure. e. None of the above. 3. For a reservoir consisting of 100 m of total thickness, of which 20 m of this thickness consist of permeable reservoir sand, the net to gross pay ratio would be defined as; a. 20% b. 80% c. 1 part in 5 d. 4 parts in 5 e. None of the above 4. Which of the following formation types has the highest grain density? a. Sandstone b. Limestone c. Dolomite 5. Which of the following is NOT a type of drilling bit commonly used in the industry? a. Percussion/air hammer b. PDC c. Orthosilicate crystal d. Diamond Roller Cone 6. The ‘flexibility’ of an immiscible interface is controlled by the; a. Density difference between the two fluids b. Viscosity ratio between the two fluids c. Interfacial tension between the two fluids d. Solids content of each fluid e. None of the above 7. Given the following air water system in which a water wet glass capillary tube is inserted and in which capillary rise of water occurs as shown, the following statement would be most correct; Gas Water a. The pressure at point B in the gas outside the capillary tube and at point A in the water inside the capillary tube is the same. b. The pressure at point B is higher than at point A c. The figure is drawn incorrectly for a water wet capillary d. The pressure at point A is lower than the pressure at point B e. None of the above 8. Which of the following factors does not impact the specific capillary pressure at a given fluid saturation level? a. Wettability b. Pore Geometry c. Surface curvature of the interface between the two fluids d. Interfacial tension e. Fluid density 9. The main disadvantage of the bulk porous method for capillary pressure determination is; a. Only one sample can be run at a time b. Very slow for low permeability samples c. Can only run with gas and water d. None of the above e. All of the above 10. A sample with a USBM wettability index of -0.70, Amott water index of 0.3 and Amott oil index of 0.6 would likely be classified as; a. Neutral Wet b. Water Wet c. Oil Wet d. Mixed wet e. None of the above 11. In a perfectly neutral well rock the height of the water-oil transition zone would be; a. Large b. Small c. Zero d. Infinite 12. A zero transition zone height would be obtained in a water-oil system if; a. The rock was perfectly neutral wet b. The capillary pressure value was zero c. The IFT was zero d. All of a to c e. None of the above 13. Micropores represent pores connected by pore throats of diameter of less than a. 0.5 microns b. 1 micron c. 2 microns d. 3 microns e. 5 microns f. 10 microns 14. Hysteresis effects in capillary pressure and relative permeability are believed to be directly attributable to differences in advancing and receding contact angle which are believed to be a function of; a. Surface roughness b. Surface wettability c. Boundary layer thickness d. Shear rate e. Interfacial tension f. None of the above 15. If we had a old set of relative permeability data where the Kro value at 20% initial water saturation had a value of 0.793, and the endpoint Krw value had a value of 0.224. If we converted the data to a ‘normalized’ relative permeability representation basis, what would the value of the Krw be in the normalized set of data: a. 1.0000 b. 0.2824 c. 0.1776 d. 0.2070 e. None of the above 16. Which one of these statements is correct concerning the value of the critical water saturation; a. It is always less than the initial water saturation b. It is always equal to the initial water saturation c. It is always more than the initial water saturation d. It can be less than, equal to or greater than the initial water saturation e. None of the above 17. When flowing perpendicular to bedding planes in contrast to flowing parallel to bedding plans the relative permeability values are generally; a. Higher b. Lower c. The same 18. In a clean state, carbonate rock surfaces are generally; a. Strongly oil wet b. Strongly water wet c. Mixed wet d. Neutral wet 19. At a constant level of interfacial tension and mobility ratio the ultimate residual oil saturation would likely be the lowest in; a. Strongly water wet rock b. Strongly oil wet rock c. Neutral wet rock 20. In a vaporizing gas miscibility process the low IFT condition is predominantly established; a. On the trailing edge of the displacement bank by extraction of intermediate components from the injection gas phase. b. Immediately upon contact with the oil c. On the leading edge of the displacement bank by the extraction of intermediate components from the oil phase d. None of the above 21. In a rich gas condensate reservoir with a critical condensate saturation of 22% and a maximum liquid dropout of 15% at the final depletion pressure level a major concern would be; a. Formation damage effects due to condensate dropout and trapping around the production wellbores. b. Loss of a large portion of the rich liquid phase due to capillary trapping effects in the reservoir c. Condensate loading and killing of the wells during later production in the life of the well d. All of the above e. None of a to d 22. The steady state method of measuring relative permeability is not used commonly for reservoir condition testing due to; a. Extensive computations are required to generate the relative permeability data b. The process in inherently unstable c. The process is very slow and time consuming d. All of the above 23. Fines migration when injecting water is more of a potential issue in; a. Water wet reservoirs b. Mixed wet reservoir c. Oil wet reservoirs d. Neutral wet reservoir e. Not impacted by wettability 24. A negative skin factor can be equated on a flow basis to a; a. Larger wellbore radius b. Smaller wellbore radius c. Zone of reduced permeability surrounding the well d. Barriers to oil flow that selectively reduce its permeability more than water flow e. None of the above 25. The most common damaging clays that contribute to fines migration problems are; a. Smectite and Illite b. Chlorite and Illite c. Illite and mixed layer clay d. Chlorite an kaolinite e. Illite and kaolinite f. None of the above PART II – DEFINITION/LONG ANSWER 1. Give four of the most important functions that a typical overbalanced drilling mud performs? (4 Marks) ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________________________________________________________ ________________________ 2. Name 10 factors that are known to impact the configuration and the endpoints of relative permeability curves (10 marks). a. _________________________________________________ b. _________________________________________________ c. _________________________________________________ d. _________________________________________________ e. _________________________________________________ f. _________________________________________________ g. _________________________________________________ h. _________________________________________________ i. _________________________________________________ j. _________________________________________________ 3. Draw comparative sets of relative permeability curves for the following three wettability types (6 Marks); PART III – COMPUTATION 1. Given the following relationship for computation of bottomhole pressure; Pcirc gh L fp Ff BPR Consider the following wellbore; Standpipe Inj Return Annulus Choke Manifold Drill String Mud Motor Given Hole Diameter – 200 mm Drill string OD – 160 mm Drill string ID – 140 mm Mud average density (assume incompressible fluid ) = 1130 kg/m3 Pump Rate – 1400 liters (1.4 m3) per minute of drilling fluid (assume overbalanced and no inflow from the formation) Well orientation – perfectly vertical Interior drill string friction factor component (in kPa per meter of flow path) = 0.35 x mud average velocity in m/s Exterior Annular Section friction Factor component (in kPa per meter of flow path) = 0.42 x mud average velocity in m/s Pressure in the formation next to the wellbore at the bit – 20000 kPa True vertical depth from the surface to the base of the wellbore – 2345 m Pressure drop across mud motor (in kPa) – 2214.6 x mud volumetric flow rate in m3/minute Assuming that the surface backpressure on the system at the choke manifold (Point ‘C”) is being maintained at a constant value of 800 kPag, what is the effective circulating bottomhole pressure at the base of the wellbore at point ‘B’ and what is the mud pump injection pressure into the standpipe at surface at point ‘A’ to maintain the given circulation rates? – Show all calculations and remember to include all appropriate friction effects (with proper sign – remember why fluids flow and how friction works), hydrostatic and backpressure effects. (20 Marks). 2. Given the following data table and plot from a conventional combined Amott/USBM test, estimate from the given curves and provided saturations (use rough integration only) the; a. The approximate USBM wettability index (USBM index = log10 (A1/A2) b. The Amott water index (Vol spontaneous water suction/total displacement) c. The Amott oil index (Vol spontaneous oil suction vs. total oil displacement) d. What would you conclude about the wettability if this reservoir based on this data (total – 10 Marks) Combined Ammot/USBM Wettability Test Results 80 60 40 Capillary Pressure - kPa 20 Water Ssturation Increasing 0 Oil Saturation Increasing -20 -40 -60 -80 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Water Saturation - Fraction Pcap Sw Pcap Sw kPa kPa 0 0.125 0 0.71 0 0.125 0 0.6 -5 0.13 5 0.4 -10 0.14 10 0.32 -20 0.18 20 0.28 -30 0.35 30 0.21 -40 0.45 40 0.16 -50 0.65 50 0.15 -60 0.7 60 0.14 -70 0.71 70 0.13 (note – the two zero capillary pressure values represent the water saturation at the beginning and the end of the static fluid exposure phase of the combined Amott/USBM wettability test) BONUS QUESTION (3 Marks) A man is in a small boat in a lake fishing. He rows to the middle of the lake and throws a 100 kg iron anchor overboard to hold the boat in place. Does the level of the water in the lake go up, down or stay the same – explain your answer clearly for full marks – no marks for lucky guesses.