Drilling in Unconsolidated Formations

Drilling in Unconsolidated Formations

You are now about to begin to drill the well and in most cases you will be drilling with a tricone bit or a larger hammer bit. In either case, the bit will be large enough to give you a hole to allow the pipe to go easily into the hole.

Assuming that you are drilling with a tricone bit in the overburden, you will attach the tricone bit to the bottom of the drill pipe or kelly depending on the type of machine you are using by means of a sub. In well drilling terminology, a sub is an adapter from one type or one size of thread to another type or size of thread. Once the tricone bit has been placed on the machine you are ready to start drilling.

You lower the bit to the ground and start the rotation at a fairly rapid 35 to 50 rpm. Then, gradually turn on the air. The air then blows through the rod, out of the bit with the bit rotation, and you are ready to start drilling. You would apply a light down-pressure to the kelly or drill pipe forcing it into the ground.

At this point you must be very careful to watch that pieces of rock or dirt are not thrown into your eyes for the air will be throwing the material at the base of the bit out in all directions since there is no hole to cause it to come straight up. As the bit rotates, the down pressure is continuously applied to cause the bit to drill its way into the ground. At this point you would not want to put heavy down-pressure on the bit for it would cause the hole to become crooked.

You would continue on with this until you had drilled the length of the kelly or drill rod, depending on the type of machine. At this point the machine rotation would be stopped, the air left to blow a short period of time to clean the hole thoroughly, and then the air would be cut off.

With a top-head drive machine you would then attach a drill rod wrench such as the centralizer fork chuck under the flat portion of the drill rod and by reversing the rotation of the head you would unscrew the joint. The drill rod wrench would hold the rod in place when the head is not attached. The head would then be raised up to the top of the derrick and a new drill rod would be connected to it, and then lowered down and threaded onto the top of the drill rod that was in the hole.

Once this is tightened up, the drill rod wrench would be removed and you would then be ready to start your rotation and air and go back to drilling. In the case of a kelly type machine you would (1) pull the kelly from the hole, (2) place your drill rod wrench on the bit sub, (3) disconnect the kelly, (4) add a drill rod to the top of the bit sub, (5) take off the drill wrench, (6) lower the new drill rod into the hole, (7) attach the drill rod wrench to the top of the new drill rod and (8) attach the kelly to the top of the new drill rod thus connecting your drive line. The wrench would then be removed, the kelly lowered into the table and drilling would resume.

While this drilling is taking place you will note that a pile of cuttings builds up around the hole. You as a helper are expected to keep this cleared away from the hole and out from under the driller's feet. You should, as standard practice, save a sample of cuttings that are coming from the hole every ten feet, or at any change of formation, to determine what formations you are passing through.

This process would be continued until you reach the top of the rock. You would then drill two to five feet into the rock to allow room to insert pipe to obtain a sanitary seal.

Once the hole has been drilled into the top of the rock, the driller would blow the hole quite vigorously to get it as clean as possible in order that he might not have any problem in placing the pipe in the hole. While the drilling is taking place, you, the helper, should be lining up casing to go into the well, measuring it, and attaching the drive shoe to the bottom of the pipe and then to the hoisting mechanism the driller uses, making it ready to go into the hole.

Once the hole is good and clean the driller will remove the drill from the hole and you will be helping to disconnect each length of drill rod as it comes out and to stack it in its proper position on the machine. Care should be used in handling the drill rod so as not to batter or damage the threads. Once all the drill rods are out of the hole and the bit taken off, you are ready to install the casing.

In the event the hammer is used to drill the overburden, the principle is the same for drilling, the only difference being that the hammer would have the action of the hammer type bit instead of the cone type bit to cut the formation. In some areas of the United States, the overburden is so loose that it is impractical to try to drill an open hole with air through the overburden. In these cases the driller quite frequently drills the overburden using the hydraulic rotary process.