Drilling Mud and its Additives
In the years since drilling muds were first used in exploratory and development wells, the technology has undergone many changes. Today, better drilling additives are used to improve the quality of drilling muds. Drilling muds are liquids that are used during drilling.
Stay with us to know drilling mud and its additives.
Drilling Mud
Drilling mud, which is also called drilling fluid, is a fluid that is sent into the well by a pump along with the drill bit. This fluid comes out of the well after the expected work is done.
Drilling mud is used for various purposes. The most important task of this fluid is to carry the drilling cuttings and to cool the drilling string and the drill bit.
Also, the drilling fluid must have sufficient density to control formation pressures, and maintain well stability. They are used to prevent damage to permeable formations by creating a filter cake to inhibit any liquid leakage.
Other duties of drilling fluids include keeping the drilling cuttings suspended when the fluid flow is interrupted, preventing the corrosion of the drilling pipes, facilitating the cementing operation, and minimizing the damage to the environment.
Classification of Drilling Fluids
In general, drilling fluids are divided into 3 categories based on their continuous phase:
- Water based fluids
- Oil based fluids
- Pneumatic fluids (gas-based fluids)
The most common drilling fluids are water-based muds. Because oil-based muds are expensive and require more environmental considerations.
Pneumatic or gas-based fluids are mostly used in underbalanced drilling operations or low-pressure reservoirs. Among the advantages of these fluids, we can mention the high speed of mud circulation and its cheapness compared to other fluids.
Water Based Fluids
The use of water-based fluid is very common. The base fluid of this mud is water. In addition to water, various mineral and chemical substances are used as additives.
Water base mud consists of liquid and solid phases.
Fresh water, salt water, saturated salt water and hard water are used as liquid phase in water-based muds.
Of course, the best type of water for making water-based drilling fluid is water that is free of salt, calcium and magnesium ions. Because these substances have adverse chemical effects and destroy the physical properties of the mud.
The solid phase of water-based mud consists of clay and additives. In general, solids are divided into reactive and inert solids.
Reactive Solids
The reactive solid phase of water-based muds consists of commercial clays, natural clays, native clays, and special native clays.
The commercial clay that is mainly used in making drilling mud is called bentonite. Bentonite by strengthening the walls of wells prevents the falling of cut stones into the well.
Native clays are mainly extracted from surface mines near the drilling site. These clays are chemically neutral and are mostly used to increase the weight of muds.
Due to their unique properties, special native clays are used in very salty waters to increase viscosity.
Natural clays are crystallizable clays that exist in some formations of the earth. This clay accidentally enters the mud during drilling and remains suspended in its liquid phase. The presence of this clay in the mud destroys its physical properties, such as kaolinite, and montmorillonite.
Inert Solids
Inert solids are chemically neutral and remain suspended in mud. These solids may have entered the mud intentionally to increase the weight of the mud . But sometimes these substances enter the fluid unintentionally, which is not pleasant like sand, limestone and dolomite.
In general, the control of the properties of water-based mud largely depends on the control of the properties of its clays. Clays have strong chemical activity in freshwater. This is while clays have little chemical activity in salty waters or oil-based mud, and their grains do not crystallize significantly. Therefore, it is easy to control the properties of these muds.
Oil Based Fluids
Oil is the base fluid of oil-based muds. Their formulation is more complex compared to water-based muds, and that’s why they have a higher price.
Shale control is one of the fundamental roles for oil-based systems. The presence of water phase with high salinity helps to prevent swelling and hydration of shales. Most oil-based fluids are composed of calcium chloride brine, which provides the best inhibitory properties over shales.
The advantages of this type of mud include excellent control in the field of controlling the loss of drilling fluid, suitable lubrication for the drilling bit, and a high ability to carry cuttings.
Among the disadvantages of using this mud, we can point out the environmental hazards and the weak connection between the cement and the well wall due to the presence of oil.
Today, it is made from crude or refined palm oil instead of diesel, which makes it more environmentally friendly.
Pneumatic Drilling Fluids
Pneumatic drilling fluids are usually used in areas where the use of conventional drilling mud is ineffective. In these fluids, air, foam or aerated fluid is generally used to circulate the cuttings out of the well hole.
In pneumatic drilling operations, a lot of specialized equipment is needed to ensure the safe management of cuttings. Also, the presence of tanks, lines, compressors and valves related to gas is needed so that the drilling operations have proper efficiency.
Pneumatic fluids are basically composed of dry gases such as air, natural gas, N2 and CO2.
In general, these fluids are considered harmless to productive formations.
Drilling Fluid Additives
Drilling fluid additives are one of the most important materials that are added to drilling fluid. These materials are added in solid form to the liquid phase of drilling mud. The solid phase of drilling mud refers to materials that are added to the liquid phase by the user. Sometimes these materials have entered the drilling mud from the formation and during drilling.
The amount of these materials in the drilling fluid varies from 5 to 50%. Solids may be active or inactive.
Active solids have a physical and chemical effect on the drilling fluid. Among these materials, we can mention bentonite, salts, polymers, as well as any material that is added to mud to change its viscosity.
Inactive solids are materials that only have a physical effect on the drilling mud, such as barite and limestone powder, which only increase the weight of the mud.
If these materials (active and inactive) enter the drilling mud from the formation, they may cause undesirable changes in the drilling mud, which are also called harmful materials, such as sand.
As mentioned, a wide range of drilling fluid additives are used today. Clays, polymers, weighting agents, fluid loss control additives, gilsonite, dispersants or diluents, inorganic chemicals, and surfactants are the most common types of additives used.
The most important functions of conventional drilling mud additives are:
- Increasing Density
- Control of Fluid Loss
- Surfactants
- Loss of Circulatory Control
- Diluters
Increasing Density
Additives such as barite are often added to drilling fluids to increase density. This is done to provide the necessary hydrostatic pressure in the depths of the well. Increasing the density of drilling mud prevents the penetration of fluids from the formation into the well. It also inhibits the destruction of the well due to high pressure during drilling. Various materials are used to increase the density of drilling fluids, including siderite, calcium carbonate, hematite, ilmetite, and galena.
Control of Fluid Loss
To prevent the loss of drilling fluid, it is necessary to add additives to improve the filter cake properties.
Filter cake properties such as thickness, hardness, uniformity and cake permeability are very important. Because the formation of an unsuitable cake can cause many problems in drilling. Additives like bentonite, clay, dispersants ,and polymers such as starch are usually added to drilling mud to improve filter cake properties.
Surfactants
Surfactants reduce the surface tension between contact surfaces between phases. These materials are used to change the colloidal state of clay from fully dispersed to controlled flow.
Loss of Circulatory Control
In terms, the loss of the entire drilling fluid in the subsurface is called lost circulation. It usually occurs in fractured rocks and permeable sandstones due to increased pressure. Special materials are used to prevent additional losses of drilling fluid during the operation. Materials such as fibers, crushed car tires, calcium carbonate, marble, formica and mica are used.
Diluters
The thick filter cake narrows the space between the pipe and the well. Diluents are used to improve fluid loss control and reduce filter cake thickness.
These substances reduce the tendency of mud to form mud cakes. Quebracho, which is a type of tannin, is used as a mud thinner and to fight cement contamination.
Other Additives
There are many other additives for drilling fluids. To control pH, lime, caustic soda, soda ash and bicarbonate of soda are used.
Fluids full of starch (especially salt mud) contain bactericides to kill bacteria.
They also use soda ash, bicarbonate of soda, caustic soda and non-specific polyphosphates to reduce calcium in seawater and treat cement pollution.
Next, Infinity Galaxy as an international supplier of gilsonite and bitumen introduces Gilsonite which is one of the drilling mud additives.
Gilsonite
Gilsonite (natural asphalt or natural bitumen), also known as Uintahite or Asphaltum, is a pure hydrocarbon with a melting point between 160 and 220 degrees Celsius.
Gilsonite has been discovered in different regions of the world, but its large-scale production is mainly observed in Iran.
Gilsonite is found as a black, hard substance with a shiny surface. Due to the fragility of this material, it is supplied in the form of lumps and powder.
Gilsonite as Drilling Mud Additive
Lost circulation occurs when the fluid encounters fractures or formations of very high permeability (such as a gravel bed and vugular limestone).
As mentioned, lost circulation can be overcome by adding materials to the drilling fluid.
To solve this problem, common granular additives including gilsonite, expanded perlite, plastic and crushed walnut shells are used.
Gilsonite is used in drilling fluids and oil well cement. Gilsonite is used as an additive to control high temperature and high-pressure filtration in drilling mud.
Adding refined gilsonite to water-based drilling fluids minimizes wellbore damage by stabilizing problematic shales and removing highly permeable sands.
Addition of gilsonite to oil well cements reduce slurry weight without loss of compressive strength. It is also an effective blocker for sealing fractures in weak formations during cementing.
Among the other advantages of gilsonite, it can be said that it prevents the accumulation of sediments and therefore the drilling tool is less trapped. Also, gilsonite delays the erosion of the well, and as a result, drilling the well becomes easier.
Another feature of this material is that it has a very high adhesive strength. For this reason, it is impermeable to water.
Gilsonite is one of the materials used to drill deep wells. This material is also used to dig deep wells in the seas.
Typically, gilsonite powder used in drilling mud has a particle size of about 45-75 micrometers, ash content range of 5-10%, softening point between 185-220°C.
In general, the use of gilsonite in drilling has advantages such as the following:
1- The resulting slurry has a low density without adding a large volume of water
2-Stabilizer of problematic shales
3- This material is compatible with other additives and is resistant to acidic, alkaline and corrosive materials
4- It resists the hydration of the slurry
5- The temperature range of its use is wide
6- As a result of pressure, it does not become lumpy or colonized
7- During the cementing of oil wells, it closes the seams and cracks of the well.
