Drilling rigs are composed of various systems, which has a specific task in drilling operations. Due to the fact that drilling methods has changed from impact to rotary drilling, drilling rig systems have become more complex and consist of more parts. Depending on the type and depth of drilling, the specifications of the formation etc. other drilling systems may be added to the below systems. In general, it can be said that each drilling rig consists of the following main systems.
Power is the energy required to start an engine. Drilling rig power system provides required power for drilling by internal combustion engines that use diesel fuel. The use of gas fuel engines is also becoming popular. Number of required engines depends on the depth of the well being drilled.
The power generated by mechanical and electrical actuators is transmitted to the components of the rig. In mechanical rigs, power is transmitted to the rig components by a set of belts, chains, and wheels. The drilling rig power system in most drilling rigs for deep and semi-deep wells is electric. This is because maintenance and installation of these types of rigs is easier than mechanical rigs.
Drilling rig systems, with the help of a hosting System, guide the drill pipe string into or out of the well. The Hosting System is also responsible for piping the well. The hosting system includes Substructure rig (steel structure), drilling draw works (sometimes called hoist), Crown Block, Traveling Block, hook and drilling cable. The hosting system includes substructure rig (steel structure), drilling draw works (sometimes called hoist), Crown Block, Traveling Block, hook and drilling cable.
Substructure provides the necessary support for the rig and rotary table structure. Therefore substructure and rotary table can withstand the load applied by the drill pipe string either when suspended in the well or when it is placed on the rig structure. In addition, the height of the substructure is adjusted to provide space under the drilling rig for large blow out valves. Drilling draw works, drilling control panels, doghouse and other equipment are located at the bottom of the drilling rig. These equipments are located at suitable distance from the ground due to the height of the Substructure).
Draw works in the drilling rig systems are also called hoists. Drilling draw works is a very large winch that twists the drill wire to move the drill pipe and drill string up or down.
Drilling cable, called a cable or wire rope, is made by twisting several steel wires. This cable is designed to withstand heavy loads in the drilling rig. Drilling wire or cable must be wrapped around a Draw works on the rig, so stringing-up is required.
The rotary system, as an important part of the drilling system, is responsible for rotating the drill pipe and drill bit.The rotary system includes:
Recirculation system circulates the drilling fluid to the drill and then transfer it to the ground for treatment and reuse. For rotary drilling, the fluid must circulate downward through the drill pipe string around the drill and then flow upward through the annular space between the drill pipe string and the well wall. Drilling mud after passing through the drill pipe string, comes out of the drill nozzles and moves from the annular space to the wellhead.
The recirculation system uses the following equipment to circulate, purify, and recirculate the fluid:
If the recycling system uses air or gas to circulate the fluid, the compressor must also be added to the above equipment. The main purpose of using the mud circulation system is:
The drilling fluid is usually liquid and sometimes it can be air or gas. Most of the liquid fluid is water with oil (usually diesel fuel). Drilling mud pump is one of the most essential components of a fluid circulation system. The pump pressure pushes the fluid from the fluid chamber through the drill pipe string to the drill and the depth of the well. It then returns to the pit through the empty space between the well wall and the drill pipe string.
Well control system is used to prevent eruptions. Well eruption is the uncontrolled flow of gas, oil or other fluids in the well into the space outside the well or underground layers. This condition occurs when the pressure inside the formation is greater than the pressure applied to it by the drilling mud. A well eruption can destroy a drilling rig, waste oil, and possibly damage the environment. Fluid (oil, gas or salt water) erupts at very high pressure from the wellhead. The fluid coming out of the well often ignites, especially in cases where the fluid contains gas, and becomes a roaring fire. Well control equipment includes the following components: B.O.P., Accumulators, Chokes, Choke Manifolds. The drilling rig system uses the following equipment in the control section: B.O.P., Accumulators, Chokes, Choke Manifolds.
In addition to the main equipment of drilling rig system, other additional is required. Power, lifting, rotating, recycling and well control systems have additional equipment that is added to the main equipment and prepares the drilling rig for drilling operations. The number and type of this additional equipment depends on the type of drilling rig. In addition to these effects, other factors such as land conditions, weather, distance from service centers and transportation should also be considered.
To start the operation of modern drilling rigs, AC generators are used, which mostly work with the help of diesel fuels or natural gas. This motor-generator set is used to generate the required power of drilling catapults, rotary tables and drilling mud pumps. In addition to the above, the energy produced by this system is used to set up the rig, shale shaker motors, mud pit agitators, centrifugal pumps, engine cooling fans and other ventilation systems.
Most of these generators are capable of generating 50 to 350 kW of energy. In some cases, larger units with more power are also used. In general, one of these generators is responsible for generating the required power of a drilling rig without considering the energy required for the Hosting system, rotary and pumping. The second unit of the generator motor system is used as the first set of storage. The second unit of the generator motor system is used as reserve the first set of storage.
In mechanical rigs a small compressor producing compressed air, provides the required air for clutches and pneumatic controls. The compressor has a tank to store compressed air. Diesel-electric drilling rigs are rigs that supply their required power through diesel engines that drive electric generators. In these rigs, an electric compressor is used to produce compressed air with a pressure of 650 to 1000 kPa. Compressed air is used to start pneumatic controls, start main engines, pneumatic elevators, air pumps on the BOP unit and etc.
The instrumentation system is the key part of a drilling rig system. Drilling instrumentation system measures the weight of the drill pipe string, drilling mud level, pump pressure, rotational speed and other variables are measured.
Due to the high cost of maintenance and operation of drilling rig systems, the best possible type of equipment should be used. This can only be achieved by employing a skilled, experienced workforce familiar with the drilling equipment so that they can, prevent possible damages during drilling operation. Also, using up-to-date and safe equipment, in addition to reducing the operation risks associated with the work, also significantly reduces the costs of equipment failure. Safety, skilled labor and up-to-date equipment are therefore the most important issues regarding drilling rig systems and equipment.
Sama Karimi is chemical engineer, drilling fluids specialist and product manager. She’s is involved in technical aspect of chemical export project at TEAM. Her effective communication skills made her to be our contact person for many reigns.
She is chemical engineer, and drilling fluids specialist at TEAM. Before that she was a drilling fluid engineer for 3 years. In this role, she was responsible to work on new type of drilling fluids additives and specialty chemicals along with managing a team of two drilling fluids production expert. Her efforts and success in this role helped to reduce waste and general costs of mud production projects.
She is graduated from Farzangan High School and entered the chemical field at Iran University of Sciences and Technology.
Drilling mud can be considered as the most important factor in the drilling process. Any problem in the production of drilling mud or mud circulation system will stop drilling operations and result in heavy fines. Proper selection of mud circulation system is effective in preventing possible breakdowns and reducing downtime. This systems are made of different parts, which will be introduced in the following.
Drilling mud problems may be due to mud composition or the mud circulating system selection. The composition of added materials to the mud is determined depending on the drilling conditions, formation structure, drilling depth etc. For example, Hematite is added to the drilling mud composition in high pressure wells to control the pressure caused by the formation. It is clear that the selection of materials to be add to the mud requires special expertise. But in this article, without considering the composition of drilling mud, the systems used to circulate the mud in drilling are examined.
For drilling in different areas with different geological structure, the capabilities of drilling methods should be examined. Studies show that most of Iran’s oil reservoirs are tougher in comparison to many countries and the formations have many cracks. For this reason, due to the lost circulation of mud in these cracks, there is always the risk of financial cost and damages.
The main priority in drilling such formations is the use of Under Balanced Drilling (UBD) method. Also in resources that are sensitive to the penetration of fluids and solids and UBD method should be used. In formations with shale fracture cracks, due to high mud lost circulation, the use of conventional drilling methods causes lots of damage in drilling operations. In these cases, the best type of drilling is to use UBD drilling with fluids such as foam. High drilling speed is an influential factor in drilling operations in these areas. However, in formations which the well wall has low strength and stability (increasing the probability of well collapse) as well as formations that swell and reduce the diameter of the well or watery formations, UBD drilling is not recommended.
Gilsonite usage in drilling fluid is as high-temperature, high-pressure filtration control additives in drilling mud. This mineral can be used in all oil based mud and all temperatures. Also, mixed Gilsonite is used effectively in water-based mud systems.
Gilsonite powder reduce API and HPHT fluid loss in all oil-base muds. It has the ability to stabilize drilling mud and thus prevent erosion of pit. It helps improve the overall emulsion stability, Thermal stability and suspension characteristics of most oil-base formulations. Gilsonite also increase viscosity, especially at lower temperatures due to its partial solubility and reduces torque and drag.
Mud with Gilsonite creates a narrow and strong wall inside the wells. It is also used to control lost circulation in drilling formations.
The purpose of using Gilsonite in cementing oil wells is mainly to lighten the slurry and increase its volume. Gilsonite is a solid hydrocarbon that belongs to the category of asphalts. The type of this mineral used in cementing wells has fine and coarse black grains. Gilsonite used in cementing oil wells is a mixture of fine and coarse black grains. This mixture should be such that it does not block the grout channels and at the same time, it should not be too small that it cannot fill the seams and gaps of the formations. Gilsonite grain size is in range of 200-325Mesh, because these grains have low shear strength, they break under high pressure.
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