A Laboratory Study of Microemulsion Flooding (includes associated papers 6395 and 6396 )
- Robert N. Healy (Exxon Production Research Co.) | Ronald L. Reed (Exxon Production Research Co.) | Clarence W. Carpenter Jr. (Exxon Production Research Co.)
- Document ID
- Society of Petroleum Engineers
- Society of Petroleum Engineers Journal
- Publication Date
- February 1975
- Document Type
- Journal Paper
- 87 - 103
- 1975. Society of Petroleum Engineers
- 5.4.1 Waterflooding, 5.3.2 Multiphase Flow, 5.1 Reservoir Characterisation, 5.4.10 Microbial Methods, 1.6.9 Coring, Fishing, 5.2.1 Phase Behavior and PVT Measurements, 5.6.5 Tracers, 2.4.3 Sand/Solids Control, 4.3.4 Scale, 5.1.1 Exploration, Development, Structural Geology, 4.1.5 Processing Equipment, 5.4.9 Miscible Methods, 2.5.2 Fracturing Materials (Fluids, Proppant), 5.4.7 Chemical Flooding Methods (e.g., Polymer, Solvent, Nitrogen, Immiscible CO2, Surfactant, Vapex), 1.2.3 Rock properties
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According to the literature, microemulsions have open been evaluated using core floods run at high flow rates sometimes much higher than could be achieved in a reservoir, except close to an injection well. The rationale for this is, presumably, that microemulsion flooding is a "miscible-type"process. However, it is necessary to determine what is meant by these words and what relation they bear to a "miscible" process. In this paper an effort has been made to experimentally distinguish miscible from immiscible aspects of microemulsion flooding and to evaluate the contributions of each to oil recovery. Some of the principal conclusions relate to the rate dependence of microemulsion flooding, bypassing of resident fluids, nature of the external phase, surfactant retention, and mechanisms of oil recovery.
Results of a surfactant field test conducted in the Loudon field in Illinois demonstrated that a fresh-water preflush could not be employed to "condition" the reservoir so as to provide optimal salinity before surfactant injection. Even though the Loudon pilot sand was not highly heterogeneous (Lorenz coeffecient = 0.35), a 1.4-PV preflush of fresh water did not adequately displace the high salinity resident brine from the reservoir. As a result, the surfactant was exposed to higher salinities than could be tolerated. It was concluded that "pockets" of highly saline water were flushed out because of mobility improvement when surfactant and polymer slugs effectively swept the reservoir. it follows that it will be necessary to design the entire surfactant flooding process on the basis of resident brine and oil; i.e., both the surfactant slug and polymer slug must be effective in resident fluids. Preflushes can be successfully used in laboratory floods, but these floods do not model reservoir mixing. It would be desirable, then, to devise surfactant systems that are highly effective over a large range of salinities. Not having these, it is necessary to design existing for resident salinities. These observations have affected experimental procedures used in this work. Specifically, the same brine that is used as resident water and final drive water is used to prepare the microemulcon and polymer slug. This mode initial residual oil in the core is always the same as the oil component of the microemulsion slug. This mode of operation has the added advantage that laboratory core-flooding results are more readily interpreted than would be otherwise possible. Microemulsion displacement of oil and water is a complex process not well understood in all its details. A number of questions have been raised in the literature and some of these require further, more detailed study. For example, are there rate effects? Does micellar structure type make any difference? That is the duration of miscible displacement? What role is played by immiscible displacement after slug breakdown? What are the effects of bypassed water and oil and do these persist in long core floods? Some of these questions will be answered here, others explored, but there will still remain much to be done before microemulsion flooding is thoroughly understood.
CONCEPTS AND DEFINITIONS
Microemulsion displacements are referred to as miscible, or of a miscible-type, with some misgivings, possibly in view of the micellar structures always present. For some, it is difficult to think of a displacement as miscible when just below the threshold of visibility there are discontinuities having dimensions on the order of hundreds of angstroms. Thus it appears that the concept of miscibility refers to some scale and has to do with the presence or absence of interfaces. However, the scale is arbitrary and it is convenient to use visible white light as the measure. The following brief discussion is included for purposes of consistent use of terminology. As previously, one is concerned with the approximate ternary representation of oil-water-surfactant systems (Fig. 1).
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