Oil & Gas- Drilling Technologies

Oil well drilling is a complex operation and the drilling industry engages the services of personnel and a complicated array of machinery and materials to drill an oil/gas well to depths greater than 6000 meters, The drilling industry has seen technological progress, however, these advances have not changed the fact that, besides the use of complicated machinery, successful drilling is a result of tremendous team effort. Numerous personnel from the operating company and several service companies work together to drill and complete an oil/gas well. A drilling rig is used to drill a hole, and this requires qualified personnel, different types of equipment the application of a great variety of techniques.

When a drilling project is commenced, two goals must be achieved:

• To drill and finish the well in a safe manner (personal injuries, technical problems) and according to its purpose;
• To complete the project with minimum cost.

The overall costs of the well must be optimized and this optimization may influence where the well is drilled (onshore – extended reach or offshore above reservoir), the drilling technology applied (conventional or slim-hole drilling), as well as the evaluation procedures, run to gather subsurface information for future drilling projects. Rotary drilling is the most efficient technology applied in the oil and gas industry. It is a drilling technology that relies on the continuous circular rotation of the bit to break rocks, while drilling fluids circulate through the bit and up the wellbore to the surface, making it possible to drill safely and efficiently the well.

Rotary drilling rig

The drilling rig consists of a set of equipment and machinery located on the so-called drilling site and normally the rig is not owned by the oil company but by drilling service companies, which hire out the rig complete with operators and which construct the well according to the client’s specifications.

Drilling Rig Systems

A drilling rig is composed of different systems:

1. The hosting system

• It the set of equipment necessary for handling any material inside the well(drill string and the casing);
• It consists of a structural part (Derrick/mast and substructure), the complex of the crown and traveling block, the draw works (hoist) and the drilling line;
• The substructure is the supporting base for the derrick, the draw works, and the rotary table, and constitutes the working floor for operations, or drilling floor.

The Hosting System

2. The rotating system

• The rotating system allows the rotation of the drill string, and it consists of the rotary table, the Kelly, and the swivel;
• In modern rigs, top drive groups together the functions of the above three items of equipment.

   

                                                  

The Kelly System                                                               The Top Drive System

3. The circulation system

• The circulation system consists of mud pumps, distribution lines, and the mud cleaning and accumulation system;
• It is the closed hydraulic circuit which allows the mud to flow from the surface to the bottom of the hole, inside the drill string, and subsequently back to the surface, in the drill string borehole annulus;
• The mud from the hole has to have the cuttings removed before being reinjected to the bottom of the hole and the mud pumps supply the energy necessary for circulation;

Drilling fluids are subdivided into three major classes:

1. Water-based muds;
2. Oil-based muds;
3. Air-based muds (used to reduce bottom hole pressure, to avoid circulation losses in surface layers, or to limit damage to productive formations).

The Circulating System

4.  The power generation system

• A power generation system is needed to run the machines driving the main components of the rig and it is provided by diesel engines, diesel-electric engines;
• Power is transferred from the engines to the different rig systems by belts, chains, and driveshafts on a mechanical rig, or by generated DC electrical power on an electric rig and it is distributed to the rotary table and mud pumps and to the draw works.

Drilling Rig Power Generation System

5.  The drill string

The drill string is an assemblage of hollow pipes of circular section, extending from the surface to the bottom of the hole.

It has three functions:

• it takes the drilling bit to the bottom of the hole while transmitting its rotation and its vertical load to it;
• it permits the circulation of the drilling fluid to the bottom of the hole;
• it guides and controls the trajectory of the hole.

                    

 Drill String                                   An Insert Tricone                                           Bit A PDC Bit

6.  Casing

• The casing is a steel tube that starts from the surface and goes down to the bottom of the hole and is rigidly connected to the rocky formation using cement slurry, which also guarantees hydraulic insulation.
• The casing supports the walls of the hole and prevents the migration of fluids from layers at high pressure to ones at low pressure.

Casing Strings

7.  Cementing

Cementing is the operation of pumping a cement slurry between the casing and the formation, and can be performed by injection into the annulus from inside the casing.

The cementing (primary cementing) serves to rigidly connect the casing to the formation and to guarantee the hydraulic insulation of the various formations, preventing the migration of the fluids from layers at high pore pressure to those at low pressure.

The centralization of the casing is particularly important, as the geometry of the well is seldom regular, but tortuous and with a variable diameter.

Primary cementing

Credits: Oil and Gas portal