Secondary Water Troubles.—Secondary water enters the oil zones due to five causes, namely: 1. Accidents to the casing used in shutting off the water sand.
2. Faulty cementing of the water sand.
3. Cave-ins, due to the withdrawal of a large quantity of sand from the oil stratum, thus allowing water to enter the oil zone from above.
4. Cases where no effort has been made to shut off file water formation, especially in prospect holes.
5. Water from neighboring wells.
Accidents to the casing that shuts off the water may result from the dropping of sharp-pointed tools, bailers or sand pumps into the hole, or from falling tubing. The casing may be eaten, due to the corroding action of the minerals in the water, and later collapse. The cutting action of sand in a flowing well is often sufficient to cut the casing. Sometimes the casing is defective or is not put together properly. Again, the sudden shifting of the sands in the oil zone may cause the casing to pull apart or break at the water string.
Accidents to the cement may result from the causes enumerated above, without, however, affecting the casing to any marked degree. Again the cement may be improperly mixed, the action of the water upon it may destroy its efficiency, or it may be so porous that it will not withstand the water which seeps through it and in times wears large channels. Where the water pressure is great, the cement may be ineffective.
Caving around the casing is of common occurrence in the California fields. Where large quantities of sand, often 50,000 to 100,000 cu. ft., are taken from the oil zones, there must of neces sity be left some form of cavity underground. This cavity leaves the roof above it unsupported. Where the roof consists of soft shale or clay, caving is inevitable. If the distance between the oil zone and the water stratum is slight, such a caving would assuredly admit water to the oil sand.
In cases where no effort is made to shut off water, the con sequences are often very dangerous to the life of the field. Then the water has free scope and soon floods the near-by portion of the field and later may spread over a large extent of good terri tory. "Wild-cat" drillers are especially prone to neglect the
proper precautions to shut off water. When he strikes oil the speculator sells his property and leaves the purchaser to shoulder the burden of responsibility. Sometimes these properties stand idle a long time and in consequence become worthless.
One well may make water and later flood other adjacent wells. Such water introduced into other wells may also be classed as secondary water, as improper casing methods allow this infiltra tion of water from one well to another.
Correcting Water fact that should be empha sized is that in most cases water troubles can be to a great extent eliminated, and in others entirely overcome. The methods employed are largely those of common sense and practical engineering. The beneficial results of such treatment are quite apparent. Wells that have made as much as 100 bbl. of water and only 4 or 5 bbl. of oil have, when the water was shut off, produced 10 to 20 bbl. of oil and no water.
The shutting off of water also decreased the lifting expense to a very marked degree. Wells that once pumped in the third hole were later pumped in the second, and instead of pumping 24 hr. were pumped only 4 or 5 hr. per day, which makes a large saving in expense and also in the wear and tear of rods and tubing.
Shutting off the water increased the production of casing-head gasoline on.one lease from 400 gal. per day to an average of 1400 gal., and only three wells were treated.
In starting to correct water troubles, it is essential to know: 1. Whether the water is primary or secondary.
2. Whether or not natural flooding has taken place.
3. Whether or not the well has been drilled too deep.
4. Whether or not casing trouble in the well is letting in water.
5. Whether or not water is coming from a neighboring well.
To ascertain these facts a careful survey of the property and its neighbors must be made. Natural conditions must be studied and maps and cross sections made.