| Popis: |
Abstract Brine corrosion inhibitors, varying from highly dispersed organic materials to low-molecular-weight salts, were evaluated for their effect on return oil permeabilities. Cores used in these tests were 50- to 100-md and 1,000- to 3,000-md sandstone. Temperatures up to 300F and two different density brines were studied. Results show that emulsion blockage was a problem at low temperatures for inhibitors that yielded low brine/oil interfacial surface tensions. At higher temperatures, emulsion blockage was greatly reduced. Inhibitors that produce sulfide ions resulted in reduced return permeability with cores containing iron. permeability with cores containing iron Introduction Brines are used in completion and workover operations to minimize formation damage. However, a number of additives are needed for the successful application of brines. One additive routinely used is an inhibitor to reduce corrosion of tubing and other metal equipment. These corrosion inhibitors use a variety of mechanisms to protect the metal surface. Some use dispersed "nonreactive" material to coat the surface, while others adsorb and react to produce a protective coating. Most corrosion literature is concerned with how well the inhibitor protects the metal and not how the invading brine inhibitor affects the formation permeability. permeability. Brine corrosion inhibitors are made from a variety of substances. This variety includes such materials as amine still bottoms, quaternary amines, nitrogen heterocyclics, Mannich reaction products, thioureas and organosulfur compounds. Inhibitors are generally surface active either because of the intentional addition of surfactants to solubilize and disperse various components or because of the innate surfactant-like properties of certain ingredients. These surfactant materials can adsorb properties of certain ingredients. These surfactant materials can adsorb on the formation matrix, changing the formation's wettability, and can reduce the brine/oil interfacial surface tension, allowing formation of emulsions. During completion and workover operations, brines invade the producing formation. Consequently, the permeability of the formation may be impaired by emulsion blockage or by the same mechanisms that protect metal equipment. This paper examines the impact of corrosion inhibitors on the permeability of formations. permeability of formations. LABORATORY TEST METHOD Laboratory tests designed to simulate well conditions were performed in order to study the effect of brines containing corrosion inhibitors. The permeameter used for this study had the capability of operating as a constant differential pressure or a constant flow-rate instrument. Tests run on the instrument prior to this study had shown that the 95% confidence interval was 16.7% return permeability for the constant differential-pressure operating mode and 1.8% return permeability for the constant flow-rate operating mode. To maintain constant differential pressure, the flow rate during the tests had to vary greatly. As the flow pressure, the flow rate during the tests had to vary greatly. As the flow rate varies, the shear drag of the flowing fluid on the stationary connate fluid varies which changes the residual connate water saturation. It has been well documented that any change in residual water saturation has a dramatic effect on the relative permeability. Therefore, the higher variability for the constant differential pressure mode was believed to be caused by the varying flow rates. Even though constant differential pressure more closely simulates actual well conditions, it was decided to pressure more closely simulates actual well conditions, it was decided to use the constant flow-rate mode during this study to maximize the precision of the data. A photograph and a piping diagram of the permeameter are illustrated in Figures 1 and 2.To gain more precision, all cores were stabilized in respect to the saturating "formation brine" and the oil used in the permeability tests. p. 215 |
