The goal of this research is to evaluate dilute (hence relatively inexpensive) surfactant methods for carbonate formations and identify conditions under which they can be effective.
This project was selected in response to DOE's Oil Exploration and Production solicitation DE-PS26-01NT41048 (July 2001).
University of Houston
There are many carbonate reservoirs in the United States (and the world) with light oil and fracture pressure below its minimum miscibility pressure (or the reservoir may be naturally fractured). Many carbonate reservoirs are naturally fractured. Waterflooding is effective in fractured reservoirs, if the formation is water-wet. Many fractured carbonate reservoirs, however, are mixed-wet, and recoveries with conventional methods are low (less than 10%). Thermal and miscible tertiary recovery techniques are not effective in these reservoirs. Surfactant flooding is the only hope, yet it was developed for sandstone reservoirs in the past. This project is aimed at developing an inexpensive, surfactant-based process for improved oil recovery.
Surfactants have been identified that alter wettability of calcite minerals aged with a crude oil and that lower interfacial tension. Surfactant adsorption can be minimized by the use of an alkali. Laboratory imbibition tests show about 61% oil recovery with an anionic surfactant and 37% in the case of a cationic surfactant. A numerical model has been developed that fits the rate of imbibition of the laboratory experiments. Field-scale fracture-block simulation shows that as the fracture spacing increases, so does the time of recovery.
The waterflood recovery in fractured carbonate reservoirs is typically very low. This dilute surfactant method can be used to improve the oil recovery in high-permeability reservoirs by almost 60%.
The major achievements of this project are:
This project is aimed at developing a dilute surfactant flooding process for fractured carbonates. Researchers have conducted laboratory tests with a West Texas crude oil. They have matched the experiments with mechanistic simulations. More than 60% of the oil can be recovered by spontaneous imbibition of a 0.05 percent by weight surfactant solution.
The five tasks for the project are 1) adsorption, 2) wettability alteration, 3) gravity and viscous mobilization, 4) imbibition, and 5) simulation. Researchers have finished the first three tasks and are currently working on the last two tasks, which will be completed in the next four months.
Seethepalli, A., Adibhatla, B. and Mohanty, K.K., Physicochemical Interactions During Surfactant Flooding of Carbonate Reservoirs, SPE J., 9 (4), 411-418, December 2004.
Kumar, K., Dao, E., and Mohanty, K.K.,Atomic Force Microscopy Study of Wettability Alteration, SPE 93009, Proceedings of SPE Intl. Symp. on Oil Field Chemistry, Woodlands, Feb. 2-5, 2005.
$150,000 (20% of total)