Jawaharlal Nehru Technological University Hyderabad B.Tech III Year PETROLEUM RESERVOIR ENGINEERING Previous Question Paper (February/March - 2022 - R15)

Fluid pressure regimes refer to the classification of subsurface reservoir pressures relative to the hydrostatic pressure gradient, which is the pressure exerted by a column of water extending from the surface to the depth of interest. These regimes are categorized based on how the measured formation pressure deviates from this normal hydrostatic trend.

1. Normal Pressure Regime: Occurs when the formation pressure is equal to the hydrostatic pressure of a column of formation water. The gradient is typically around 0.433 to 0.465 psi/ft.
2. Abnormal Pressure Regime (Overpressure): Occurs when the formation pressure significantly exceeds the hydrostatic pressure. This is often caused by rapid sediment burial, tectonic activity, or fluid expansion (e.g., hydrocarbon generation).
3. Subnormal Pressure Regime: Occurs when the formation pressure is lower than the hydrostatic pressure, often resulting from fluid depletion in mature reservoirs or geological uplift and cooling.

PVT analysis (Pressure-Volume-Temperature) is the laboratory study of reservoir fluid samples to determine their physical and thermodynamic properties under varying pressure and temperature conditions. It is essential for estimating original oil in place, predicting reservoir performance, and designing production facilities.

The complete PVT analysis for oil involves the following laboratory procedures:

1. Sample Collection: Obtaining representative bottom-hole or surface-recombined samples to ensure the fluid composition matches the reservoir state.
2. Constant Composition Expansion (CCE): The sample is expanded at reservoir temperature to determine the Bubble Point Pressure, isothermal compressibility, and relative volume changes.
3. Differential Liberation (DL): Gas is removed from the oil in stages as pressure is reduced at constant temperature. This measures the Solution Gas-Oil Ratio (Rs), Oil Formation Volume Factor (Bo), and gas properties, simulating the depletion process in the reservoir.
4. Separator Tests: A series of flash expansions performed at different separator pressures and temperatures to determine the optimal surface conditions for maximizing oil recovery and liquid stock tank production.
5. Viscosity Measurement: Determining the oil viscosity at various pressures to understand flow behavior through porous media.