Dynamics of Two-Phase Immiscible Pulsed Flow

Abstract

Cyclic waterflooding has received recent attention since many studies and field tests have shown that it may lead to additional oil recovery at virtually zero additional cost. Even though the process is in principle very similar to conventional waterflooding, there are interesting new effects taking place under the pulsed conditions that need to be properly quantified for a realistic field deployment of the cyclic injection process. Two-phase immiscible pulsed flow experiments performed on homogenous packed glass beads cells are compared with flow behaviour under continuous injection. In the pulsed experiments, injection is switched on/off using a timing device in the pumping system. Symmetric cyclic periods and different injection rates were used in the study. Initially the dry packed cells were flushed with CO2 and saturated with water. This was followed by injection of oil up to leaving the cells at irreducible water saturation conditions. Then water was injected and the amount of produced fluids measured. Separate experiments under continuous and pulsed injection conditions with visual monitoring of fluid displacement were performed. It is found that the amount of oil recovered at intermediate stages (after breakthrough and less than 3 pore volumes of injected water) is larger for the pulsing mode. The final recovery for both injection processes is similar within the experimental error. In the pulsed experiments, during the off injection period, spontaneous fluid spreading was observed leading to smoother displacement fronts compared to continuous injection. Also, displacement fronts were found to be more stable under pulsed conditions. The study concludes that residual oil saturation under pulsed injection can be reached earlier than under continuous injection, a result very attractive for field application. Experimental findings of this work shed light in the design of cyclic injection processes. Introduction Cyclic water injection is being considered as a potential alternative to the inherent difficulties of waterflooding since it may lead to additional oil recovery. The process itself was proposed a few years ago, and has been tested successfully in some reservoirs in USA, Russia and China, where additional recoveries in the range 2–18% have been reported, with the additional benefit of a decrease in water cut levels. Even though the process is in principle very similar to waterflooding, there is still a lack of understanding on the role of certain parameters and operational variables. Among those we may cite: reservoir wettability initial oil and water saturation, saturation history effects, oil viscosity, cyclic period selection, and reservoir heterogeneity. Cyclic water injection refers to a process in which the injection rates are changed from high to low values and then back to high, in a periodic fashion, allowing the pressure maintenance support required in the water injection process. The cyclic periods are in the range of weeks to months, a different time scale from the so called pulsed pressure technique, where short pressure pulses are applied in time intervals of a few minutes. Several authors have simulated the cyclic injection process for a variety of operational conditions. However, only few experimental works have been reported quantifying the role different variables on the process, and to clearly establish the differences with continuous waterflooding. Visualization experiments are particularly appropriate to address such objectives allowing capturing fine details about the dynamics of flow displacement. After a literature review we present the methods and the properties of the porous media and fluids used in the experiments. The cyclic water injection process is compared with the results obtained in a conventional waterflooding experiment under conditions where the same amount of fluid is injected in each case. The effect of bead size, injection rate, oil viscosity, cyclic period is reported and analyzed. Displacement front stability is addressed in the discussion section.

An Optimal Injection Scheme for Maximizing Oil Recovery in CO2 Miscible Flooding

“…This also indicates that, to achieve a relatively stable displacement in CO 2 miscible flooding, the fast oscillation of displacement rates with short periods should be used. This finding is similar to the experimental results in waterflooding by Ivanov and Araujo (2006) and the Vapex process by Muhamad et al (2012), in which the shortest cyclic periods lead to the highest oil recovery. However, the mechanisms are different because of the nature of the different displacements.…”

“…Results indicated that the pulsed tests could increase the oil recovery rates and final sweep efficiency by 10% over non-pulsed tests. Ivanov and Araujo (2006) carried out an experimental study on immiscible pulsed flow in waterflooding. Several parameters were examined, including bead size, cycle period, injection rate and oil viscosity.…”

The Impact of Tides on the Capillary Transition Zone

“…We used this approach because it was not possible to continuously change bottom hole pressure in the wells in the simulator to mimic the synthetic tidal variations. This method has been previously used by Ivanov and Araujo (2006).…”