History
The use of drilling fluids for drilling wells was first suggested in 1833 by French engineer Fauvelle. Observing a rope drilling operation in which the drilling apparatus encountered water, he noticed that spouting water very effectively removes drill cuttings from the well. He invented an apparatus in which it was supposed to pump water under the drill rod, from where the drill cuttings were washed out with water to the surface between the drill rod and the wellbore.
Types of drilling fluids
Drilling fluid formulations have changed as oil production has evolved. Over the centuries they have changed from "drilling mud" to multicomponent mixtures with adjustable in a wide range technological properties. Today there are four main types of muds - water-based, hydrocarbon-based, gaseous muds and foam. The search for the optimal drilling fluid recipe - inexpensive but effective - continues.
Water-based fluids are divided into:
- clayless drilling compositions, such as ordinary process water, all sorts of suspensions and polymer-based muds, and so on;
- clay drilling fluids based on mineralized or fresh water, as well as fluids containing gypsum, clay particles and chlorine elements.
Main Functions and Purpose of Drilling Fluids
1. Cooling and lubricating the surfaces of the drill bit. Since the work of this tool is always associated with the appearance of a lot of friction, it is necessary to use lubricating compositions that simultaneously reduce the temperature of the tool in order to increase its wear resistance;
2. Bottom-hole cleaning. Many drilling fluids make it possible to effectively wash the drilled rock out of the borehole and bring it to the surface. The quality of such cleaning depends on the physical and chemical properties of the particular composition, as well as on the geological features of the drilled rocks, therefore, in the process of preparation it is necessary to take into account the composition of rocks of a particular field;
3. Formation of a purification layer on the walls of the wellbore. The casing formed on the walls of the wellbore is characterized by low permeability, which provides stability in the upper sandy zone of the geological section and makes it possible to separate the wellbore from highly permeable layers;
4. Prevention of water, gas and oil manifestations;
5. Protecting the walls of the well against collapses that occur when drilling rocks based on unstable clay;
6. Such an important sphere of drilling compositions application as providing qualitative opening of productive horizons stands apart. Many of today's drilling fluids prevent contamination of the reservoir during drilling-in and avoid complete plugging, which makes it very difficult to develop;
7. Reducing the cost of fixing the well with strings;
8. Obtaining data necessary for analysis during the operation of exploratory wells. This is also one of the auxiliary functions of such compositions, because together with them the cuttings and particles of rocks, which are the subject of study, are brought to the surface;
9. Increasing the resistance to corrosive effects of equipment and pipes;
10. Ensuring compliance with the requirements of industrial safety and minimizing the harm caused to the environment.
Drilling Fluid Circulation in the Well
Most drilling fluids in drilling operations circulate through the following cycle:
1. The drilling fluid is mixed and stored in special tanks.
2. The mud pump pumps the mud from the tank through the drill string and into the hole.
3. The drill mud travels through the pipes to the bottom of the hole, where the drill bit breaks the rock.
4. The mud then begins to return to the surface, carrying the rock particles (cuttings) that have been separated by the bit.
5. The mud rises through the annulus, the space between the borehole wall and the drill pipe. A typical diameter of the drill pipe is about 12.7 cm. At the bottom of a deep well, it may be about 20 cm in diameter.
6. At the surface, the drilling fluid passes through a return line, a pipe that leads to a vibrating screen.
The sieve consists of a series of vibrating metal grids that are used to separate the mud from the cuttings. The solution flows through the screen and returns to the sieve.
The slurry particles fall into a trough for removal. They may be cleaned before being discharged, based on environmental and other considerations. Some cuttings particles are sampled by geologists for condition studies inside the well.
