Not only are reamers important for directional drilling, but they can also be useful in straight hole applications. Reaming assemblies can straighten out and smooth over crooked holes, restore undergauge holes to gauge, and get rid of any irregularities or keyseats. They also help to prevent excessive hole curvature in short intervals, which may be experienced when entering and exiting a section of hole which forms a sharp curve. Finally, reamers can reduce the rotational torque in a wellbore, and may therefore be used as a substitute for a conventional string or near-bit stabilizer.
Reamers are made by almost all major downhole tool manufacturers, and have the same core features: sealed or open (mud lubricated) bearings, cutter types – either “nobbly” or “smooth”, and either one (so called “3-point”) or two (“6-point”) sets of cutters in a tool.
Reamer (Courtesy of NOV, 2017)
A multilateral well is a well with two or more laterals (horizontal, vertical, or deviated) drilled from a main mother well. This allows one well to produce from several reservoirs. Multilateral wells are suitable for complex geology where drilling more new wells to penetrate to those reservoirs is not economical. Lateral sections may be used to produce from a separated section in depleted, faulted, layered and heavy oil reservoirs.
Figure 1 – Multilateral Well Bashkiria drilled in 1953 (Credit – http://www.drillingcontractor.org)
Figure 2 shows how multilateral wells fit with several geological structures.
Figure 2 – Multilateral well with different geological structure
This article demonstrates how to design the well trajectory in J-shape from the surface location to the required target depth (TD).
- The surface location coordinate of Well-A is 6,543,065.00N 416,695.00E and the target is located at 6,542,213.00N 415,456.00E and the UTM zone is 31N.
- Kick off depth = 4,200’MD/4,200’TVD
- Planned build up rate = 2 degree/100 ft
- Well profile = J-profile (build and hold)
The surface location coordinate of Well-A is 6,543,065.00N 416,695.00E and the target is located at 6,542,213.00N 415,456.00E and the UTM zone is 31N. Therefore, the surface and the target for Well-A can be illustrated is Figure 1. Continue reading
Nowadays, many wells required complex well trajectory plans in order to reach reservoir sections and some of complicated well paths (Figure 1) cannot be drilled with either rotary drilling assemblies or mud motors. In order to achieve the drilling goal, rotary steerable tools are usually selected.
Figure 1 – Complex Well Paths
While the precise mechanics might vary, each rotary steerable tool uses much the same approach. Running the rotary steerable immediately above the bit serves as a sort of replacement for a near bit stab (NB stab). Most tools use three blades close to the drill bit, which act as stablizers and move in and out. While the tool turns, the blade which is turning in the opposite direction pushes against the side of the hole, giving the necessary side force to create a curved hole while drilling.
When using a steerable motor, the adjustment of the well path a series of slide drilling and rotary drilling doesn’t give a clean smooth edge, but rather creates a hole with multiple sharp edges, and straight sections between them. A rotary steerable tool, on the other hand, does give a smooth curved hole. This makes the wellbore more stable, and less resistant when tripping in and out of the hole. With higher inclinations, a smooth curve makes for an easier job of running casing or logging tools. Continue reading
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).
Figure 1 – A build rotary assembly