Drilling fluid is a circulating fluid that meets the needs of drilling operations and has various functions during the drilling process. Drilling fluid is the blood of drilling fluid, also known as drilling fluid cleaning fluid. According to the composition of drilling fluid, drilling fluid can be divided into clear water, mud, clay-free washing fluid, emulsion, foam and compressed air. Clear water is the earliest drilling fluid and is suitable for untreated, easy-to-use areas with intact rock formations and ample water sources. Mud is a widely used drilling fluid, which is mainly used in formations with unstable pore walls, such as looseness, development of fractures, blocky, water swelling, and spalling that are prone to collapse.

Drilling fluid has at least the following 10 functions:

Sweep the bottom of the well, carrying debris. Keep the bottom of the well clean, avoid repeated cutting, reduce wear and improve efficiency.

Reduce the cooling of the drill bit and drill string and lubricate the temperature of the drill bit, reduce the wear of the drill bit, and increase the service life of the drill bit.

Prevent oil and gas reservoir contamination and wellbore collapse.

Balance (control) formation pressure, prevent blowout, lost circulation, and prevent formation fluid from contaminating drilling fluid.

Hanging debris and dosing. Reduce debris settling velocity to avoid settling.

Sand and debris can sink to the ground.

Efficient transmission of hydraulic power. It transmits the power required by the downhole power drill bit and the hydraulic power of the drill bit.

Weight portion of drill pipe and casing. The buoyancy effect of the drilling fluid on the bit and casing can reduce the load on the hoist system during trips.

Provide a large amount of formation data, and use drilling fluid, electrical measurement, debris measurement and other methods to obtain downhole data.

The rock was hydraulically broken. The high-velocity jets of drilling fluid passing through the nozzles can either directly break or help break up the rock.

Basic type

According to the dispersed continuous phase, drilling fluids can be divided into water-based drilling fluids, oil-bearing drilling fluids, gas drilling fluids, etc.

Drilling fluid is mainly composed of liquid phase, solid phase and chemical treatment agent. The liquid phase can be fresh water, brine, crude oil, diesel oil or emulsions (mixed oils and inverse emulsions). Solid phases include useful solid phases and unwanted solid phases. Chemical treatments include weapons, organic and polymeric compounds.

Water based drilling fluid

Water-based drilling fluid is a sol-suspension mixing system with water as dispersion medium, bentonite, metering agent and various chemical treatment agents as dispersion phase. Its main components are water, clay, metering agents and various chemical treatment agents.

Water-based drilling fluids can also be divided into:

(1) Fresh water drilling fluid.

(2) Brine drilling fluids (including seawater and brine drilling fluids).

(3) Calcium-treated drilling fluid

(4) Saturated brine drilling fluid.

(5) Mixed emulsified (oil-water) drilling fluid.

(6) Non-dispersed low solid phase polymer drilling fluid.

(7) Potassium-based drilling fluid.

(8) Polymer drilling fluid.

Oily Drilling Fluid

Petroleum continuous phase drilling fluid is a sol-mixing mixing system with crude oil or crude oil as dispersion medium and weighting agent, chemical treatment agent and water as dispersion phase. Its main components are crude oil, diesel oil, weighting agent, chemical treatment agent and water. It basically goes through crude oil drilling fluids, organic drilling fluids and oil-water (inverted emulsion) drilling fluids.

(1) Crude oil drilling fluid.

(2) Oil-bearing drilling fluid.

(3) Oil-in-water (anti-emulsification) drilling fluid.

Gas drilling fluid

Gas drilling fluid is a kind of drilling fluid with air or gas as drilling fluid.

Foam drilling fluid is a drilling fluid with foam as drilling fluid, and its main components are liquid, gas and foam stabilizer.

Drilling fluids are generally divided into 8 systems: non-dispersed solid polymer drilling fluids, freshwater drilling fluids, brine drilling fluids, saturated brine drilling fluids, calcium-treated drilling fluids, potassium-based drilling fluids, oil-based drilling fluids, and gas drilling fluids.

Drilling fluid is the "blood" of drilling and plays a very important role in drilling work. Therefore, drilling fluid requirements are very high, mainly in four aspects.

Drilling Cycle Requirements

The requirements of drilling fluid for drilling fluid are low viscosity, strong sand carrying capacity, low static shear force, good lubricating performance and low friction. Fewer solid particles.

Keep the borehole wall stable.

During drilling, the drilling fluid pressure column and formation pressure are used in the formation to achieve equilibrium, and the drilling fluid density is stable. The drilling fluid density thermally balances the oil and gas pressure through the drilling fluid pressure. Drilling fluids need to overcome unstable formations.

Drilling fluids are required to protect oil and gas reservoirs.

In order to prevent the drilling fluid from causing damage to the oil and gas formation, the water loss of the drilling fluid is small. Thin mud cake (after the drilling fluid loses water, the drilling fluid forms solid pressure solid particles in the oil well to form a mud ring), the solid content is low, and the hydration degree of the filtrate is low (after the filtrate enters the formation).

Important role

The harsh environment of underground drilling operations promotes the research and development of drilling fluids. During the drilling process, key tasks such as suspension, pressure control, rock stability, buoyancy, lubrication, and cooling must be carried out.