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1. (80) Let us consider the flow term between cells follows Darcy's equation where flow is proportional to the pressure difference between two grid cells. Grid cells are rectangular in the xy plane. We can write: Q = T x DC (delta P), where DC is the dynamic constant updated at every time step, and T is the transmissibility. For flow in the x direction, if we double the delta x in both cells, how does this effect the transmissibility between cells?
Answer: (E) Transmissibility is decreased by a factor of two
Explanation: Flow in the x direction goes through the y-z area cross section. So cross sectional area remains unchanged. When I double delta x in both cells, the x distance between grid centers also doubles.
3. (40) A highly cemented rock is likely to have a lower formation factor, F, than a slightly cemented rock of the same porosity.
Answer: (B) False
Explanation: For 10% porosity, an uncemented rock can have an m value as low as 1.3, resulting in an F factor of 10, while a highly cemented rock will can have an of 2.2, resulting in a F factor of 100.
4. (30) Oil can not be found in igneous or metamorphic rock.
Answer: (B) False
Explanation: This is certainly not the natural habitat for oil and gas, as metamorphic and igneous rocks are formed by high temperatures. Hydrocarbons, if present in these rocks, must have migrated after their cooling and consolidation.
6. (20) You have the following log response from an oil bearing limestone formation in a well filled with fresh water as well as the chart below. Compensated bulk density = 2.46 g/cc, Interval transit time = 60.0 microsec/ ft, Matrix transit time = 47.6 microsec/ft, fluid transit time = 189.0 micosec/ ft. The secondary porosity in this zone is most nearly:
7. (60) For gas well tests in widely spaced, low permeability fields, where the tests are conducted at a series of increasingly flow rates, the calculated open flow potential will be underestimated.
8. (90) In a water well, with a specific gravity of 1, one bubble of gas is trapped at the bottom of the well (8000 ft deep) when the well is shut in. The surface pressure is atmospheric when the well is shut in. The gas bubble expands to 8 to 12 times its original volume when it comes to the top of the well. What is the maximum wellhead pressure possible? What is the maximum bottom hole pressure? Neglect gas deviation factor and assume constant temperature.
10. (10) The assumption not used in the derivation of the radial flow form of the diffusivity equation is:
Answer: (D) Flow into the wellbore continues after well is shut in
Explanation: The diffusivity equation is the fundemental to reservoir simulation and well test analysis. Well test analyses uses the diffusivity equation and adds to it (or superimposes on the pressure response), early wellbore effects.
11. (100) A drawdown and buildup test has been conducted. Pressure response shows no boundaries. Semi-log analyses have been conducted on both drawdown and build-up tests and a straight line slope has been identified. There is some positive skin. However, the line includes some pressures affected by wellbore storage. What effect will this have on the calculation of permeability?
Answer: (E) Permeability will be underestimated in both analyses.
Explanation: Drawdown- pressures above infinite acting period will be included, so overestimation of m, and underestimation of k.
Buildup - pressures below the infinite acting period will be included, so overestimation of m and underestimation of k occurs.