This paper deals with a field application of foam forming surfactants injected into the Pembina Ostracod 'G' Pool to reduce the gas mobility and to improve sweep efficiency.
The presentation describes the laboratory evaluation of a number of surfactants considered to be suitable for such an application. A field injection setup and the pool performance after injection of two different amounts of the selected surfactant are described.
Even though this surfactant application was not designed as a research project with detailed instrumentation, the preliminary assessment of the effectiveness of surfactant injection 15 encouraging. The response at producing wells indicates improvement in the oil field performance.
Most improved recovery processes involving gas injection are plagued by problems related to the unfavorable mobility ratio of injected gas and displaced fluids. A coinjection of small amounts of brine containing foam forming surfactants seems to be an emerging technology showing promise in alleviating these problems.
In addition to numerous laboratory studies of foam rheology in porous media. there have been field tests of this technology in a number of steam flooding applications.1 More recently, as the problems related to the dissolution of foam forming surfactants in high salinity brines are being overcome, a number of field applications is under consideration in reservoirs subjected to hydrocarbon miscible floods, especially in Beaverh111 Lake carbonates and Gilwood sands.2
This paper deals with an application of foam forming surfactants in a gas flood 1n the Pembina Ostracot 'G' pool into which the aqueous surfactant solution was injected simultaneously with the natural gas stream to improve sweep efficiency. Laboratory procedures used for selecting the surfactant, the field injection sequence, and the production response are described.
There are no universally accepted procedures for the selection of foam forming surfactants for specific rock/fluid systems. Thus direct evaluation of effective mobilities of injected fluids was chosen as the most appropriate measure of surfactant effectiveness.
Mobility reduction factor (MRF) was selected as the best quantity for a relevant comparison of various surfactants. HRF is defined as the ratio of pressures measured across the length of the core during Simultaneous injection of the liquid and gas phases:
Equation 1 (available in full paper)
The numerator is the pressure attained when the injected liquid contains surfactant. and the denominator is the pressure attained when the 1njected liquid contains no surfactant. Thus higher values of HRF indicate a more effective surfactant, while MRF equal to one indicates an ineffective surfactant.
The displacement apparatus used for the determination of MRF is shown schematically in Figure 1. Its main features include:
The experimental procedure for MRF determination involved the following sequence. First the core was excracted with a mixture of 87% chloroform and 13% methanol to remove the remaining resident oil. Absolute permeability to air was measured next. The core was then evacuared, filled with carbon dioxide, evacuated again, and imbibed with filtered brine (0.45 µm). Several pore volumes or brine were then injected to stabilize the pressure drop across the core for calculating the absolute brine permeability.
