The project goal was to characterize the phase and emulsion behavior, surfactant retention, and condensate recovery for cosurfactants such as ethanol, crucial factors for increasing recovery of condensate in gas-condensate fields. Phase work would obtain optimal salinity and temperature in which all three phases coexist. These tests were to be performed with a condensate and with a comparable refined hydrocarbon, for varying concentrations of brine and cosurfactant (ethanol) and for a wide range of temperatures within the reported bound seen in gas-condensate reservoirs.
This project was selected under DOE's Historically Black Colleges and Universities Program.
The major factors causing hydrocarbon losses in a reservoir during production of gas and gas-condensate fields are related to pressure depletion, retrograde condensation, and water encroachment. The most widespread and simple method of producing gas and gas-condensate fields is by depletion, utilizing only the natural reservoir pressure. The major disadvantage of this method is low condensate recovery.
The ultimate condensate recovery from gas-condensate fields is 30-60%, depending upon the initial content of condensate in the gas. By comparison, the final recovery of gas in dry gas fields can be up to 95%. Despite the low recovery of condensate associated with natural depletion, this method is still widely used in the majority of the world's gas-condensate fields. The reasons for this are both technological and economic. In order to improve recovery of condensate from gas-condensate fields, innovative methods are required, as is a greater understanding of fluid behavior in such reservoirs for secondary recovery efforts.
Phase work was completed, including salinity and temperature scans and coreflooding experiments. An experimental system for electrical conductivity measurements was set up, tested, and calibrated. Conductivity measurements for conjugate pair phases were completed by April 2005.
Achieving increased production in partially depleted gas and gas condensate fields is essential for many gas producing companies. Incremental production in mature fields can be very profitable, especially in developed countries. Worldwide, the potential for production and improved recovery from gas-condensate fields is considerable.
Project tasks called for researchers to perform:
Detailed measurements and analyses were performed on ethylbenzene and condensate for a broad range of salinity and temperatures, inversion hysteresis of the emulsions was determined, and the cosurfactant was subjected to corefloodings to obtain surfactant retention and condensate recovery efficiency information. Salinity and temperature scans, emulsion inversion measurements and analyses were performed at Morehouse College. Coreflooding measurements and analyses were performed at Surtek, Inc., Golden, CO.
All measurements were made using ethanol as the cosurfactant. Surtek provided the condensate obtained from a U.S. gas-condensate field. Ethylbenzene was chosen as the refined hydrocarbon to be tested because it has the equivalent carbon number of the condensate. The phase behavior of ethylbenzene resembled that of ethane. Ethylbenzene simplified the experiments and reduced their cost by allowing the testing to proceed at atmospheric pressure instead of the high pressure required by ethane.
Measured conductivity data were compared with the predictions and completed by the end of summer 2005.
Presentations were made at the spring 2004 seminar series of the Department of Physics and Dual Degree Engineering, Morehouse College, Atlanta, GA, and at the DOE/SPE IOR conference in Tulsa, OK, in April 2004.