In this article, we discussed types of gas well, each type serves a specific purpose and requires unique drilling and completion techniques.
Gas wells cater to various geological formations, drilling techniques, and production strategies, enabling the extraction of natural gas resources from diverse reservoirs.
There are a number of different types of gas wells that can be drilled. A particular well type may be best suited or most economical in the efforts to drain a specific configuration of hydrocarbons. Various drilling strategies can be adopted to place wells in specific patterns with the aim of optimizing production from a field.
There are several types of gas well, including:
Conventional wells
In the early days of the oil industry, drilling wells was a simple operation. A well location was picked at top reservoir, and the well was drilled directly down to the target as a vertical well. Then drilling became more sophisticated when the art of deviating wells was perfected. Here, the drill bit is deflected at an angle from the vertical toward a specific target. Drill into a single reservoir, typically with a single layer of permeable rock.
Vertical and moderately deviated wells are called conventional wells. They are the most common well configurations because they are relatively cheap to drill.
Sidetrack wells
A typical operation is to sidetrack a well. This is where a well has already been drilled or partly drilled and there is a need to exit out of one side of the well to a different target. A sidetrack may be required if there is an object stuck in the original hole, which cannot be fished out. In producing fields, an existing well may be sidetracked if there is no further use for that well, e.g., the oil well has watered out. A window will be cut in the casing of the original well by a special milling assembly, and drilling will then proceed out of the window toward a new target.
Horizontal wells
Drill horizontally to access more reservoir area, increasing production potential. Horizontal wells are wells where the reservoir section is drilled at a high angle, typically with a trajectory to keep the well within a specific reservoir interval or hydrocarbon zone. In a strict sense, these wells are rarely perfectly horizontal, but they tend to be near horizontal mostly, generally at an angle greater than 80° from vertical.
Horizontal wells are drilled in a specific configuration. The tangent section of the well is drilled along a deviated well path to just above the reservoir section, to what is known as the kick off point. From the kick off point, the well is drilled at an increasingly higher angle, arcing around toward an angle close to horizontal. The point at which the well enters (or lands on) the reservoir is called the entry point. From there on, the well continues at a near-horizontal orientation with the intention of keeping it substantially within the reservoir target until the desired length of horizontal penetration is reached.
Designer wells
Designer wells are types of high-angle or horizontal wells that have more than one intended target. This makes them more cost effective because the individual targets would have otherwise required several conventional wells to drain them effectively. One aim of a designer well could be to penetrate and drain more than one fault block. In mature fields, multitarget infill wells can increase the chances of finding an economic volume of oil.
READ: Nigerian Petroleum (Drilling and Production) Regulations
Multilateral wells
Drill multiple branches from a single wellbore, accessing different reservoirs or areas.
Multilateral wells are wells that have more than one branch radiating from the main borehole. Each branch can drain a separate part of the reservoir and produce into a common single wellbore. The advantage of multilateral wells is that, for the same number of drainage points, they can be somewhat cheaper than if separate wells had been drilled.
Coiled tubing drilling
Coiled tubing is continuous, small-diameter steel pipe stored on a reel at the surface. Coiled tubing can be used in place of drill pipe for new wells and short-length to medium-length horizontal sidetracks (typically with a step-out of less than 800 m [2625 ft]). A mud turbine and drill bit combination is used for coiled tubing drilling. The turbine is powered by the mud moving through it; the tubing itself does not rotate. The advantage of coiled tubing drilling is that the drilling operation is quicker than normal drilling in that the connection time involved with a jointed drill pipe is eliminated. The tubing is simply rolled in and out of the well.
Through tubing rotary drilling
Through tubing rotary drilling is a relatively inexpensive method of creating a short-length to moderate-length sidetrack of an existing well. Slim-bore drill pipe is used to drill the well, and the benefit of this is that the drill pipe is narrow enough to be run through the existing production tubing. This eliminates the time and cost involved with pulling the completion in an existing well to start drilling and then rerunning it after the well has reached total depth.