Abstract

Mobilization of the residual oil by surfactant flooding involves a complex process not fully understood. The injected surfactant slug interacts with formation brine, oil, and the mineral surface. Usually, only the effluent production is available for analysis and history matching of the surfactant core floods. In this paper the analysis is enhanced by measuring the in situ saturation profiles directly during the displacement.

In order to analyse the fluid propagation during a surfactant flood, we have measured the one dimensional saturation distribution along the core as a function of time. The fluid saturation profiles are analysed by a moveable Germanium detector, measuring the radiation from a nuclear tracer added to the brine phase. The dynamics of the saturation profiles are obtained by scanning the core several times during the displacement. The measured saturation profiles are found to correlate well with the observed effluent production.

We focus on the description of recovery improvement, how the local saturations are developing during the surfactant floods and how well numerical simulations match the results from the experimental displacements.

Introduction

Surfactant flooding is perhaps the most complex of the oil recovery processes. However, the potential for increasing-the production from some oil fields is high. All aspects of injection of surfactants in a reservoir, at the proper conditions, must be evaluated. Important parameters describing the mechanisms of a surfactant flood include phase behavior (binodal curves and tie lines), interfacial tensions, phase viscosities, relative permeabilities, adsorption and sweep efficiency. The major factor controlling the process of chemical flooding is incorporated in the dimensionless quantity, capillary number, Nc, which is defined as the ratio of Darcy-law pressure gradient to capillary forces described by the interfacial tension. Healy and Reed have discussed immiscible microemulsion flooding, and have related mobilization of oil by lowering of interfacial tension to the fractional flow, fo. The interpretations of the development of in situ saturation fronts have been summarized by Larson et al., using a simple analytical approach to describe the saturation fronts of both miscible and immiscible displacement with respect to chemical flooding.

Surfactant flooding displacements in Clashach sandstone cores are reported. The surfactant slug consists of a mixture of two alkylaryl-sulfonates, no cosolvent is added to the surfactants. The 1-D brine distribution along the core as function of time is obtained by use of a nuclear tracer, Na in the form of NaCl, added to the brine phase.

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