Gupta, Surendra P., SPE, Amoco Production Co.
Abstract
This paper presents results of laboratory experiments and computer simulation studies of the micellar/polymer fluids injected in the Sloss field, NE. The paper shows that the dispersion coefficient for the partitioned sulfonate in the oil phase can be an order of magnitude larger than the dispersion coefficient in the water phase. The results show that the two principal components of the micellar fluid (sulfonate and polymer) propagate at different rates because of partitioning and dispersive mixing effects. Sulfonate is produced much earlier than polymer and is concentrated in the produced oil. Sulfonate partitions into the oil phase as a consequence of ion exchange, and the polymer remains in the water phase. The oil phase that contains the partitioned sulfonate i.e., upper-phase microemulsion-has high mobility. The increased dispersion coefficient for a component in the nonwetting phase, in this case the partitioned sulfonate into the oil phase, is supported by an independent study. These mechanisms contribute to early sulfonate breakthrough and a larger sulfonate requirement per barrel of oil displaced than anticipated for a nondispersive displacement. The results of this paper can be beneficial for design of other micellar fluids and performance predictions and interpretation of micellar floods in other fields.
Introduction
A micellar/polymer pilot was conducted in the Sloss field, Kimball County, NE. Interpretation of the performance of micellar pilots aids in the development of a prediction model. To meet this objective, process variables (e.g., compositional effects) must be separated from field variables (e.g., reservoir description and operating variables), and the process mechanism must be identified. Concurrent with the pilot, research continued on the process mechanism of the micellar/polymer fluids injected in the field test. This paper presents an example of partitioning and dispersive mixing effects in micellar flooding. The paper demonstrates that detailed core effluent analyses in conjunction with numerical simulation studies can reveal displacement mechanisms within the two mixing zones. These zones are between an oil/water bank and a micellar slug and between the micellar slug and a polymer bank. Results of previous studies of the first portion of the mechanism research have been published. Before discussing the results of this paper, the following provides a brief summary of the previous studies. A separate paper discusses results of a Sloss pilot post-test evaluation well.
Previous Studies
The fluids designed (see Appendix A for details) for the Sloss pilot involved a salinity contrast (or gradient) concept. The salinity of the preconditioning and the makeup brines for the micellar fluid was 12,000 ppm NaCl added to the available Sloss fresh water. The low-salinity fresh water was used for the polymer water. The following summarizes pertinent results of the previous studies. The results showed that the designed micellar fluid forms a middle-phase microemulsion when a volume of the micellar fluid is mixed with an equal volume of crude oil. A middle-phase microemulsion is in equilibrium with excess oil and water phases. A lower-phase microemulsion is generated when the salinity is less than 10,000 ppm NaCl. A lower-phase microemulsion is in equilibrium with an excess oil phase. The final oil saturation after micellar flooding (Sof), in small slug tests, increases as micellar fluid salinity decreases from the designed value. Furthermore, Sof is dependent on the capillary number (viscosity × velocity interfacial tension).
SPEJ
P. 481^
The role of the rheological properties of non-newtonian fluids in controlling dispersive mixing in a batch electrophoretic cell with Joule heating
