Cation Exchange and Chemical Flooding

Abstract

JPT Forum articles are limited to 1,500 words including 250 words for each table and figure, or a maximum of two pages in JPT. A Forum article may present preliminary results or conclusions of an investigation that the present preliminary results or conclusions of an investigation that the author wishes to publish before completing a full study; it may impart general technical information that does not war. rant publication as a full-length paper. All Forum articles are subject to approval by an editorial committee. Letters to the editor are published under Dialogue, and may cover technical or nontechnical topics. SPE-AIME reserves the right to edit letters for style and content. The ionic composition of surfactant systems is an important determinant of system performance. This is reflected by the use of prefloods to displace formation waters considered too saline and/or too "hard" and by limitations placed on the ionic composition of the water used in the surfactant fluid. Recent literature reflects a growing concern about the role of the reservoir clay in determining the in-situ composition of the surfactant formulation. In this article we show a laboratory example of a low-salinity preflood that, because of cation exchange with clays, results in a threefold increase in divalent cation (Ca++ and Mg++) concentration in the front of the surfactant flood, We outline the basic concepts required to model the reversible changes in cationic composition that result from cation exchange and indicate the general direction of our research efforts on this important aspect of surfactant flooding. Disaggregated Tar Springs sandstone with a cation exchange capacity of 0.44 meq/100 gm was used to prepare a 1 -in.-diameter, 2-ft-long sand pack. We prepare a 1 -in.-diameter, 2-ft-long sand pack. We saturated the pack with a saline Tar Springs formation water (Fig. 1) and flowed 3.8 PV of this water through the pack at a frontal advance rate of 1 ft/D and a temperature of 85 deg. F. We then displaced the formation water with a "preflood" containing 7.5 percent formation water mixed with a fresh lake water. After 1.5 PV of preflood injection, steady-state composition was achieved. The flood was continued to a total preflood injection of 4.4 PV. After this pack equilibration period, 3.7 PV of a PV. After this pack equilibration period, 3.7 PV of a chemical slug prepared in lake water containing 5 percent formation water were injected. Steady-state composition was achieved after 1.5 PV. As shown in Fig. 1, the preflood "loaded" the clays with calcium and magnesium. The "denuded" chemical slug water and the front portion of the chemical slug "unloaded" these cations from the clays. The concentration of divalent cations in the front part of the chemical slug increased from 0.0153 to 0,051 meq/ml. Calculated as Ca++ only, this is equivalent to an increase from 306 to 1,020 ppm, an amount sufficient to radically alter interfacial and viscometric properties of the system. Various equations describing the relation between cation distribution on a clay surface and composition of the equilibrium solution have been given in the literature. For the experiment reported, simple mass-action equations adequately describe the equilibria between clays and brine solutions but, as used, do not adequately do scribe the equilibria with the surfactant system. These equations are (1) and (2) where C and C are the concentrations of the indicated cation associated with the clay and equilibrium solution, respectively, both expressed as milliequivalents per milliliter of pore volume. Applicable values of K and K may vary with the type of clay, an ionic strength parameter. and temperature. Thus, each reservoir may present a parameter. and temperature. Thus, each reservoir may present a new experimental evaluation problem. P. 1336

Evaluation of surfactant flooding using interwell tracer analysis

“…The divalent ions among the electrolyte brine composition play a strong role in ion exchange from the clays to the flowing phases, and this ion exchange affects the effective salinity (Hill et al 1977;Pope et al 1978;Hirasaki et al 2011). Since the microemulsion droplets have a great affinity for divalent ions, they act as a flowing ion exchange medium (Hirasaki 1982;Hirasaki and Lawson 1986).…”

Recent Advances in Surfactant EOR

“…The phase behavior of anionic surfactant systems is much more sensitive to a change in divalent ions (e.g., Ca 2+ and Mg 2+ ) compared to monovalent ions (e.g., Na + ), especially at low surfactant concentrations (Nelson, 1981). This is problematic in sandstones because of ion exchange between the clay, brine and surfactant micelles (Hill, et al, 1977;Hirasaki, 1982). This exchange can result in the phase behavior becoming over-optimum with resulting large surfactant retention (Glover, et al, 1979, Gupta, 1981.…”

“…Whether the salinity is constant or a salinity gradient is used, the electrolyte composition is further challenged by divalent ions in the formation brine and ion-exchange from the clays to the flowing phases (Hill, et al, 1977;Pope, et al, 1978;Glover, et al, 1979, Gupta, 1981. It was discovered that the surfactant micelles or microemulsion droplets have an affinity for divalent ions similar to that of the clays and thus act as a flowing ion-exchange medium (Hirasaki, 1982;Hirasaki and Lawson, 1986).…”

Novel Large-Hydrophobe Alkoxy Carboxylate Surfactants for Enhanced Oil Recovery

“…The coreflood experiments were designed with favorable salinity gradients to maximize the robustness of the corefloods (Glover et al 1979;Pope et al 1979;Hirasaki et al 1983;Levitt et al 2009). The cores were evacuated and then saturated with the synthetic formation brine that was followed by the injection of brine to measure the brine permeability.…”