Drilling

In the oil and gas industry, well drilling is performed with a drilling rig. In this stage, the rocks are drilled by the rotation and force applied on a drill bit located in the extremity of a drill string, which consists of collars (thick walled pipe) and drill pipes (thin walled pipes). During this process, cuts are formed and removed through the injection of drilling fluid or mud, to allow for the drainage of debris through the annulus of the well.  

The main components of a rig are listed bellow:

 The derrick supports the entire load and enables the setup of the rest of the equipment.  

The crown block supports the entire load that is transmitted to it through the drilling line (steel line).

The traveling block is suspended by the drilling line, at the bottom there is a loop that holds the hook. Along with the crown block, the traveling block makes up a pulley system that moves the drill string, allowing it to descend and ascend within the well. 

The drill string is suspended within the hook by a swivel, which allows for the injection of the drilling fluid through the interior of the string, it returns through the annulus by making perforated cuts. The traveling block-hook system is moved by the energy from the draw works, which winds and unwinds the drilling line, moving the drill string.  

The rotary table transmits rotation to the drilling line while the mud pump supplies enough energy for the drilling fluid to circulate and transport the cutting out of the well through the annulus.

In Brazil, the drilling of oil and gas wells began onshore in the 1930s, and the first discovery took place in 1939, in Lobato, Bahia. Offshore drilling began in 1968, and the first discovery of oil in the coast of Brazil occurred the following year, in the Guaricema field, in Sergipe. In the mid-1970s the first oil discovery in the Campos basin took place, leading to the expansion of drilling activities in this basin and to a great number of discoveries. The Santos basin is a major highlight in the development of Brazilian petroliferous basins, because enormous pre-salt section discoveries were made in it.     

In order to perform drillings in ultra deep waters and under high-pressure conditions it is necessary to use the appropriate drilling rigs. The oil industry offers many different drilling rig options, which are selected according to the drilling objective, considering characteristics such as the location, the water depth that needs to be perforated, the final depth of the well, the production volume, and the characteristics of the expected oil

Drilling rigs can be fixed or floating. To learn more about them, click here.

There are four different types of oil wells: vertical, horizontal, directional, and multilateral, and the decision about what type should be drilled depends on the cost analysis of the drilling, the location, and the reservoir’s characteristics, as well as the location of the available rig.   

Vertical wells are drilled vertically into the area of interest. QGEP produces gas in the Manati field through this kind of well.

Directional wells are drilled when the objective is to reach an area of interest that is not found vertically in the direction of the wellhead.

Horizontal wells are drilled when the objective is not only to reach an area that is not found vertically in the direction of the wellhead, but also to maximize the contact with the reservoir and, consequently, increase the well’s productivity. These are the types of wells used for oil production in the Atlanta field.

For a same project, vertical wells are the least expensive while the horizontal wells are the most expensive, this cost is not the determining factor in the decision because the well’s productivity may vary enormously depending on the chosen methodology. Multilateral wells are used when the objective is to produce several wells simultaneously, using the same wellhead. Vertical wells are more commonly used in the exploratory phase, and are also widely used in onshore production, since the drilling costs are smaller than those of offshore wells. The Manati gas production wells are vertical.    

A well’s drilling is divided into multiple phases. After each phase it is necessary to cover up the section in order to ensure that it is safe to proceed to the next; this process is repeated until the final objective of the well is achieved. This casing is simply a column which is smaller in diameter than that of the bit used in the drilling; its role is to isolate the well from the formations and to support it. 

Last updated on 2015-05-04T15:32:06

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