SPE Members
Abstract It has been known that steamflood efficiency can be increased by adding surface active agents to steam such that foam can be generated, preferentially reduces permeability to steam in preferentially reduces permeability to steam in previously invaded zones, and diverts it through previously invaded zones, and diverts it through undepleted regions of the reservoir. In this study the partial results of a continuing project which aims to optimize surfactant use as additives in steamflood field applications are reported. Two steps of the project were completed up to date. As a first step, the foamability of seventeen surfactants was evaluated at steam injection conditions (160 degrees C and 75 psig) and linked to their chemical structure. As previously reported by D. C. Shallcross et. al., a linear model saturated with only water was used to compare and characterize different surfactants as steamflood additives. During the experiments surfactant solutions were injected as slugs into the sand pack after steam breakthrough. Nitrogen was injected as a non-condensible gas. The evaluation of foamability is based on pressure gradient changes and steam mobility reduction along the model. Under the conditions of the experiments, the alpha olefin sulfonates generated the strongest foam at low concentrations. Internal olefin sulfonates, linear toluene sulfonates and linear xylene sulfonates all generated stable foams at higher concentrations. Flow resistance due to foam also increased as the alkyl chain length increased.
In the second step, first the previous experiments were repeated by using eight selected surfactants to check if they were reproducible. During the runs two 10% PV slugs of surfactant solution with 0.5 weight percent concentration were injected into the sand pack. The second slug was injected after the foam created by the first one completely collapsed. Then these runs were repeated under the same operating conditions as the water runs except for the presence of oil. West Newport crude oil was used at residual saturation after steam flooding during these runs. The analysis of the results showed that both the pressure gradients and the reduction in steam pressure gradients and the reduction in steam mobility after surfactant solution injection were affected by the presence of oil. In the presence of oil no increase in pressure was observed to date.
The two sets of experiments were compared and discussed in detail using maximum pressure drops and duration of pressure changes, pressure increases with distance from the inlet and time, steam mobility reduction, and thermal parameters. One interesting result is the fact parameters. One interesting result is the fact that relative permeability to steam was reduced to between 0.005 and 0.02 when no oil was present. present
Introduction Steam injection is the most common method used in thermal oil recovery.
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