"Packers are usually employed for testing with the idea of continued use for remedial purposes. The common packer makes use of an ex panding rubber to effect a seal. Although the rubber is decomposed in time by oil and water, such packers are frequently left in wells for permanent correction of water troubles. Hemp has been used success fully in this connection, and will probably endure longer than rubber. The efficiency of a packer may sometimes be increased by caving for mation or by the addition of mud or sand put in from the surface.
Muddy Water Used to Indicate Leak in Casing.—" The point of entry of water into a well may sometimes be determined by using thin mud fluid or muddy water. The well should be filled as high as practicable with muddy water, with a hole open to bottom or otherwise. The fluid should then be bailed off of the top, and a careful watch kept to note the thinning of the mud and the appearance of clear water. As the fluid level is lowered in the hole, the head of infiltrating water will again overbalance the fluid column in the well, with the result of thinning up the mud with clear water. As soon as the bailer has reached the point of inflow, it will pick up practically clear water. The point of inflow is thereby approxi mately located.
Dyes and Colorless Substances Used for Tracing Underground Flow of Water.—" Suitable dyes can sometimes be used to good advantage for indicating underground fluid connections and the direction of movement. Dye can also be used for testing the efficiency of a water string.
"The world war has greatly retarded the use of dyes since 1914, due to scarcity and prohibitive prices. Varying degrees of success have accompanied experiments in connection with oil field conditions. Some dyes are decolorized by the reducing action of petroleum compounds, and by hydrogen sulphide, or are absorbed by mud and formations. Such dyes are usually unsuitable for oil well purposes.
"The subject has not received the attention it merits, but it seems likely that experimentation will now be undertaken to determine the best dyes and best methods of application. Some of the dyes that are absorbed or reduced by crude oil may be used successfully when the fluid carries a large percentage of water. The following case noted in the Casmalia field by the writer will serve as an illustration. Seven pounds of red dye, which was probably one of the aniline group, was placed in the bottom of a well. Samples of water from the neighboring
producing wells were taken frequently, but no color was at first noted. The production of water in this area is in excess of 50 per cent. One of the samples, after standing for several days, turned pink. The water produced in this area carries easily noticeable amounts of hydro gen sulphide, which gas was possibly responsible for the temporary decoloration of the dye. Upon standing exposed most of the gas passed off from the sample, and a regeneration of the color of the dye was effected.
"It is said that the dye eosin is not affected by hydrogen sulphide, nitric acid, magnesium sulphate, sodium hydroxide, alcohol or gaso line. The price and supply however, prohibit its use at present.
" The United States Geological Survey has used fluorescein extensively for tracing the flow of underground waters in connection with water supply problems. It is said to be a delicate dye which is only slightly affected by the normal ingredients of natural waters; to be decolorized by acids and affected by sdme forms of unstable organic matter. A loss of color due to acidity can be restored by making the sample alkaline.
"A demonstration with dye is reported from the Midway field. Ten lbs. of red aniline dye was used, and the time required to appear in a neighboring well was four days. In another instance in the same field, 10 lbs. of green dye demonstrated underground connection between wells after two hours and forty-five minutes had elapsed. In this case the coloration at the point of sampling lasted about 30 hours. Although the flow of water from one well to another had been suspected, failures to demonstrate it have been made where 50 to 100 lbs. of dye was used.
"The chemical nature and intensity of a dye will influence the amount that should be used for a given set of conditions. In testing the effi ciency of a water string 2 to 5 lbs. of good dye would probably suffice, while for use to show underground flow, 10 lbs. or more would be advisable. When testing a water string, the dye is put behind such casing and washed down with a stream of water. The pumping of the well should not be suspended. The appearance of dye in the production will indicate a casing leak or defective shut-off. When testing for under ground connection, the dye should be released at the bottom of the suspected well, and this well remain shut down during the time of test.