Drilling Rigs and Technologies
3.1
Drilling rigs and technologies
3.1.1 Introduction
The term drilling indicates the whole complex of operations necessary to construct wells of circular section applying excavation techniques not requiring direct access by man. To drill a well it is necessary to carry out simultaneously the following actions: a) to overcome the resistance of the rock, crushing it into small particles measuring just a few mm; b) to remove the rock particles, while still acting on fresh material; c) to maintain the stability of the walls of the hole; d) to prevent the fluids contained in the drilled formations from entering the well. This can be achieved by various drilling techniques. In this chapter rotary drilling rigs will be examined. These are, in practice, the only ones operating today in the field of hydrocarbons exploration and production. The drilling rigs used on land are complexes of mobile equipment which can be moved in reasonably short times from one drill site to another, drilling a series of wells. In particular, the typical rotary rig for drilling onshore medium to deep wells, indicatively more than 3,000 metres, will be described below. Rigs for shallower depths use analogous but somewhat simpler techniques because of the smaller stresses to which the rig is subject. See Chapter 3.4 for offshore drilling. In rotary drilling the rock is bored using a cutting tool called the bit, which is rotated and simultaneously forced against the rock at the bottom of the hole by a drill string consisting of hollow steel pipes of circular section screwed together. The cuttings produced by the bit are transported up to the surface by a drilling fluid, usually a liquid (mud or water), or else a gas or foam, circulated in the pipes down to the bit and thence to the surface. The rotation is transmitted to the bit from the surface by a device called the rotary table (or by a particular drive head), or by downhole motors located
directly above the bit. After having drilled
Drilling rigs and technologies
3.1.1 Introduction
The term drilling indicates the whole complex of operations necessary to construct wells of circular section applying excavation techniques not requiring direct access by man. To drill a well it is necessary to carry out simultaneously the following actions: a) to overcome the resistance of the rock, crushing it into small particles measuring just a few mm; b) to remove the rock particles, while still acting on fresh material; c) to maintain the stability of the walls of the hole; d) to prevent the fluids contained in the drilled formations from entering the well. This can be achieved by various drilling techniques. In this chapter rotary drilling rigs will be examined. These are, in practice, the only ones operating today in the field of hydrocarbons exploration and production. The drilling rigs used on land are complexes of mobile equipment which can be moved in reasonably short times from one drill site to another, drilling a series of wells. In particular, the typical rotary rig for drilling onshore medium to deep wells, indicatively more than 3,000 metres, will be described below. Rigs for shallower depths use analogous but somewhat simpler techniques because of the smaller stresses to which the rig is subject. See Chapter 3.4 for offshore drilling. In rotary drilling the rock is bored using a cutting tool called the bit, which is rotated and simultaneously forced against the rock at the bottom of the hole by a drill string consisting of hollow steel pipes of circular section screwed together. The cuttings produced by the bit are transported up to the surface by a drilling fluid, usually a liquid (mud or water), or else a gas or foam, circulated in the pipes down to the bit and thence to the surface. The rotation is transmitted to the bit from the surface by a device called the rotary table (or by a particular drive head), or by downhole motors located
directly above the bit. After having drilled
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