JNTU B.Tech IV ENHANCED OIL RECOVERY TECHNIQUES Previous Question Paper (February/March - 2022 - R15)

The primary objective of Enhanced Oil Recovery (EOR) is to increase the ultimate recovery of oil from a reservoir by improving displacement efficiency and sweep efficiency beyond what is achieved by primary and secondary recovery methods. It specifically targets residual oil trapped by capillary forces or bypassed due to reservoir heterogeneity.

EOR processes are categorized into three main types:

1. Thermal Recovery: Involves injecting heat into the reservoir to reduce oil viscosity, making it more mobile. Common methods include steam flooding, cyclic steam stimulation, and in-situ combustion.
2. Gas Injection (Miscible/Immiscible): Utilizes gases such as CO2, nitrogen, or hydrocarbon gases. Miscible displacement reduces interfacial tension between oil and the injected gas to near zero, enhancing oil mobilization.
3. Chemical Flooding: Involves injecting chemical agents such as surfactants, polymers, or alkaline solutions. Surfactants reduce interfacial tension, polymers improve sweep efficiency by increasing water viscosity, and alkaline agents react with crude oil to form in-situ surfactants.

Tarner’s method is a material balance-based prediction technique used to estimate the performance of a solution-gas drive reservoir. It relies on the simultaneous solution of the material balance equation and the gas-oil ratio equation to determine the pressure decline and oil production over time.

The method operates through the following steps:

1. Without Gas Injection: The reservoir is divided into small pressure increments. For each increment, the method calculates the amount of oil produced and the corresponding gas-oil ratio using the reservoir's relative permeability curves. The cumulative production is tracked until the abandonment pressure is reached.
2. With Gas Injection: The procedure is modified to account for the injected gas volume. The material balance equation is adjusted to include the injected gas term, which effectively slows the rate of pressure decline. The calculation assumes that the injected gas occupies pore space and potentially increases the oil saturation in the vicinity of the production wells, thereby altering the instantaneous gas-oil ratio.

By comparing these two scenarios, Tarner’s method allows engineers to quantify the incremental oil recovery gained from pressure maintenance via gas injection, providing a predictive tool for reservoir management decisions.