In producing systems several chemicals may be injected into a common line without regard to effect of one inhibitor upon the other. This paper examines the effect of various commonly used treating chemicals upon the efficiency of four commonly used scale inhibitors.
The generally accepted practice of chemical treatment in the oilfield is basically "use what ever materials are necessary to get the job done." Unfortunately little if any thought is given to the possible interactions between the different species of treating materials and the result of that interaction.
This paper demonstrates some of the possible results of incompatibility between scale inhibitors and other chemical treating compounds normally employed in water handling systems in the oil field.
Testing was carried out on the tube blocking type apparatus using a 0.02" PEEK tubing one meter in length as the test coil. The coil was immersed in a constant temperature water bath at 150 F. The brines were pumped through the test coil using peristaltic type tubing pumps.
Flow through the test coil was maintained at a constant 5.0 milliliters per brine, for a 10.0 milliliter per minute total flow rate. The pressure increase on the test coil was measured with a pressure transducer and a computer program to assimilate the data and display it in graphical form.
The scale Inhibitor under evaluation was added to the anion brine in all tests. Other chemicals were added to the cation brine.
All evaluations were carried out using the synthetic brine whose composition is shown in Table 1.
Commercial finished compound blends rather than the pure base inhibitor were used in all of the testing.
When working with completely water soluble materials, the required amount of compound to be evaluated was added to the cation brine. As previously noted the scale inhibitor was added to the anion brine.
With the oil soluble materials a slightly different approach was used. An amount of hydrocarbon equal to the amount of brine was mixed with the brine. (Making a 50/50-kerosene/brine mixture). In the testing depolarized kerosene was used as the hydrocarbon.
Kerosene and brine were added to a separatory funnel to which the required amount of scale inhibitor and other test material was also added. The separatory funnel was shaken vigorously by hand for one minute to assure intimate mixing. The fluids were then allowed to stand undisturbed for a period of one hour to allow the layers to separate. Water was then drawn off and used for the actual test procedure. The presence and amount of any emulsion layer was noted and recorded.
This hydrocarbon extraction procedure was used only with the oil soluble materials.