The percussion method of drilling, cable tool, churn drills, sputter, or pounders it’s sometimes referred to, is one of the oldest cutting actions utilized in the drilling industry. Developed in China over 4,000 years ago, the cable tool is tried and true, responsible for millions of successful wells around the world. This system is still used today because of its own unique advantages, which include one person operation, low equipment cost compared to other systems. Simple, rugged design requiring minimal maintenance. Low horsepower requirements of this rig, and finally cable tools have proven to be virtually indestructible. These machines are mainly used today for drilling in unconsolidated materials and soft rock formations where relatively shallow depth wells are required approximately 100 feet or less. Slow penetration rates are characteristic of this drilling system.
Support equipment required for this drilling process are basic, a small truck with welding equipment, torches and a small amount of makeup water. A separately mounted deck engine powers the rig. The cable tool uses the percussion cutting action, utilizing a 1,200 pounds real string, and usually a carbide button bit. This bit goes up and down once per second, performing four important drilling functions at once, penetrating the material beneath the bit, reaming the sides of the hole, crushing the geology into fine particles and mixing these cuttings with water.
The drilling action in conjunction with approximately five gallons of introduced water mixes with the cuttings, which require bailing after approximately four feet of drilling. This flushing system requires the drill string to be tripped out of the hole and the bailer to be tripped into the hole. The bailer is simply a hollow tube with a check valve on the bottom, which fills with the cutting slurry mixture. The action of the dart valve enables the bailer to collect cuttings for ID and recording purposes as per regulation 9903 as well as removing accumulating cuttings by dumping them in the mud spa. The bailer is also useful for measuring approximate water pumping rates and levels at any time during the well construction. The cuttings from the borehole are usually well mixed and small in size, representing an accumulation of the formations encountered since last bail.
Cable tool drillers have developed the ability to interpret the feel of the drill string to improve well log accuracy and in identifying aquifers. The cable tool drilling process typically consists of drilling, removing the cuttings, identifying the geology, monitoring the waterflow, if present, and then advancing the casing. There are two methods for casing advancement, the drive cap and the drive blocks. The drive cap is primarily used by cable tool operators until such time as increased friction is encountered.
The drive blocks that enable more energy to be transferred, to assist with driving the casing down. The casing advancement continues in overburdened situations until such time as a suitable aquifer is encountered, or until the casing is firmly seated in bedrock after which casing is no longer required as the geology itself or rock stabilizes the hole. The large bull reel shown here supports the cable, which in turn supports the drill stream. The speed at which it is turning here is typical of hole advancement in unconsolidated material. Ideally, casing is added in 10 foot sections to improve efficiency. Additional casing sections are usually welded, ensuring a watertight seal as required per regulation 903. The annular space between the working casing of the permanent casing is commonly grouted after borehole construction.