An Oil-Coating Process To Stabilize Clays in Fresh Waterflooding Operations(includes associated paper 6405 )
- J.H. Barkman (Shell Oil Co.) | A. Abrams (Shell Development Co.) | H.C.H. Darley (Shell Development Co.) | H.J. Hill (Shell Development Co.)
- Document ID
- Society of Petroleum Engineers
- Journal of Petroleum Technology
- Publication Date
- September 1975
- Document Type
- Journal Paper
- 1,053 - 1,059
- 1975. Society of Petroleum Engineers
- 1 in the last 30 days
- 141 since 2007
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A new approach to stabilizing clays has been developed that uses an oil-soluble surfactant to coat the clays with a tenacious film of oil. Two alternative formulations of the oil-coating treatment an emulsion of diesel oil and an aqueous system consisting of a dispersion of the surfactant in brine have been developed.
In some waterflood operations it is necessary to inject fresh water when a suitable brine is not available or is too costly. If the reservoir rock contains interstitial clay that swells and disperses in fresh water, permeability may be impaired and injection rates may be lowered. Many methods of stabilizing clays are based on ionic composition of the water or the use of hydrolyzed metallic cations. This paper describes a new approach to stabilizing clays that uses an oil-soluble surfactant to cause the clays to be coated with a tenacious film of oil. Following laboratory development, the oil-coating technique was field tested. It is an effective and inexpensive method giving protection from fresh-water impairment. Two alternative formulations of the oil-coating treatment have been developed: (1) an emulsion of diesel oil, containing the oil-wetting surfactant, in brine (referred to as the OC emulsion), and (2) an aqueous system consisting of a dispersion of the surfactant in brine (referred to as the OC dispersion). The second method, which uses the residual oil in the formation to coat the clays, is less expensive and is generally preferable. However, it is not effective with certain heavy crudes, for which the first method must be used. Both methods are applied as a batch treatment that affects only a small radius around the wellbore. Since the pressure drop decreases under conditions of radial flow with the log of the distance from the wellbore, a treated zone of about 10 ft is generally adequate. Usually, the treatment is preceded by an acid job so that the formation may be cleaned and brought to maximum permeability before being stabilized.
It is recommended that laboratory tests of the treatment be made before applying it in a new waterflood. This is best done by measuring the relative permeability to fresh water of preserved cores from the reservoir at residual oil before and after treating with the oil-coating process. The effect and comparability of acid and acid additives also should be checked. In principle, the optimum volume of treatment may be determined by assuming various radii of treated zones, substituting into the radial flow equation treated and untreated permeabilities as determined from the cores, and comparing the resultant injection rates and costs.
Laboratory Evaluation of the Oil-Coating Systems
Oil-Coating Emulsion Testing
The OC emulsion was formulated with two considerations in mind: (1)that it should be effective in stabilizing the clays, and (2) that it should be fine enough to be injected easily into the formation. The composition of the emulsion is given in Table 1 and the function of each ingredient is as follows. The agent that causes the sand grains to become oil wet is Redicote 75 TXO, a cationic surfactant. Another cationic agent, E(11), is added to stabilize the emulsion. A nonionic agent, E(12L), controls the fineness of the emulsion. The diesel oil or toluene provides a low-viscosity oil to coat the sand grains.
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