Shock subs, also known as vibration dampeners, are used to absorb vibrations and bit shock loads in drill collar strings. They usually feature long integral elastomeric elements, which serve to transmit torque and weight to the bit simultaneously. When drilling is being carried out at shallow depths, intermittent hard and soft streaks, along with broken formations, can transmit vibrations to the surface, where they are easily detected. With greater depths, though, these vibrations might not be detected because the drill string cushions them. However, they will still cause damage to the bit, as well as bottom hole assembly components and the drill string.
Shock Sub (Vibration Dampeners), Hunting (2018)
Some advantages of using a shock sub include:
Offering faster drilling rates, since optimum bit weight and rotary speed may be used on the bit constantly.
Increasing the bit length by reducing shock loads.
Cutting damage to drill collars, drill pipe, and downhole tools by reducing bouncing.
Reduced connection damage, because the elastomeric element absorbs both torsional and axial loads, so that connections are not at risk if the bit stalls.
Reduced damage to surface equipment, including swivels, blocks, and wirelines.
Rotary drilling assemblies can typically control a directional of a well by having proper stabilizer placement. With this kind of drilling assembly, only inclination can be controlled and a well cannot be directionally oriented to required direction. In this article, it briefly describe how stabilizer placement can affect the well direction.
Rotary Build Assembly (Fulcrum Assembly)
When a drill collar is supported at both ends but not held vertically, its own weight causes it to sag in the middle. This phenomenon is used in rotary drilling assemblies to create the necessary side force at the bit to alter the angle (Figure 1).
Even outside the drilling industry, the concept of directional drilling, whereby a drill is precisely guided through a particular target, is a fascinating one. This article will describe about applications of directional drilling in oil and gas industry. Later on, we will discuss in several aspects of directional drilling such as directional drilling tools, well path design, wellbore navigation tools, etc. Let’s get started.
Why Drill Directional Wells?
It is a fact that it is always more expensive to drill a deviated well to a target not directly below the rig location, as opposed to simply drilling down vertically to the target.
However, there is good reason why a directional well might be used: in some circumstances, it can actually lower the total cost of the project. Some potential reasons for this include:
Multiple exploration wells from a single wellbore
It is possible to drill a well to evaluate it, and then cement it back up. This well may then be deviated from its original path to an additional target. This may be done in order to evaluate multiple compartments in a single reservoir, if it is naturally split into several sections, or to extend the knowledge of the structure using a single well.
Figure 1 – Example of Multiple Exploration Wells from a Single Wellbore
Scale factor represents distortion from a mapping system since the Earth is mapped into a flat surface, but the actual surface is in curvature. Figure 1 illustrates a scale factor with a reference location of the Earth’s surface. If the location is above the map projection plan, the scale factor will be less than 1.0. However, if the location is below the mapping projection, the scale factor will be more than 1.0. A scale factor less than 1 means that the actual distance on the Earth’s surface is longer than the actual distance on the map. Whereas, the scale factor of more than 1 demonstrates that the actual distance on the Earth is shorter than the map distance.