Drilling mud may lose its properties when in contact with different layers of the earth, so the drilling mud should be evaluated at specific intervals and its lost properties should be compensated.
As a result, some chemicals and minerals are added to drilling fluid to reduce viscosity, improve mechanical and rheological properties of mud, improve cake filter properties, increase well stability, prevent formation degradation, reduce jelly properties, control colloidal behavior and prevent lost circulation. The choice of these additives depends on factors such as rock strength, fracture rate, depth, gaseous material, drilling method and mineralogical composition of the rocks. The importance of these factors has caused the production of drilling mud additives to face many complexities.
The general purpose of using drilling mud additives is filtration control, pH control, mud viscosity control, increasing the weight of drilling fluids, controlling fluid waste into the formation, protecting pipes and other chemicals that are effective in improving drilling mud performance.
In this paper, first the types of drilling mud additives are studied, then gilsonite and barite, which are widely used in the production of drilling mud additives, are examined. Gilsonite powder is a drilling mud additives which is used to control the viscosity of the mud, loss circulation and creating filter cake. The second additive in drilling mud that has been studied is barite, which plays an essential role in controlling pressure and increasing the density of drilling mud.
Types of drilling mud additives
Drilling mud additives are divided into several categories. The production of each drilling mud additive is done with different formulations according to the type of drilling and the structure of the formation.
- Weighting materials for drilling mud: Weighting materials include calcium chloride, salt, barite and calcium carbonate.
- Drilling mud viscosity enhancers: Increasing the viscosity increases the strength of the mud for raising the drilling stumps to the ground. Bentonite is one of the most widely used materials in this sector.
- 3) PH control substances: In most muds pH is kept between 9.5 and 10.5. The penetration of H2S in the drilling mud acidifies the environment and reduces the pH and increases the corrosion. For this purpose, the pH is raised even above 10. Caustic soda and calcium hydroxide are chemicals used to regulate the pH of mud
- Lost circulation control: In the drilling process, when high permeability sandstones or rift formations are encountered, some mud penetrates into the formation and causes lost circulation. At the same time, the solid particles inside the mud adhere to the surface of the formation and prevent further wastage of the mud, creating an edge called a cake filter on the surface of the formation. Materials such as bentonite, polymers, gilosonate powder and mica are used to control lost circulation in drilling fluids.
Gilsonite is a glossy black substance composed of various high molecular weight hydrocarbons and has a wide variety of colors, hardness, specific gravity and volatile constituents. From the accumulation of sediments of plant-derived compounds among the rock layers and the effects of microbial activity, pressure and heat over time, coal is formed. This coal is later changed to semi-bitumen. As the process continues, the charcoal hardens and turns into Gilsonite.
Gilsonite has several uses, including the manufacture of oil and gas pipe coatings, as an additive for drilling mud, the manufacture of industrial bitumen, the use of drilling cement, the extraction of heavy metals and its use in road construction.
Application of Gilsonite in drilling mud
In drilling oil and gas wells, Gilsonite is mainly used for cementing wells and reducing the weight of drilling mud. The most important role of Gilsonite in drilling is to prevent wastage of drilling fluid and its loss into the formation. Gilsonite must be combined with other materials such as mica to be effective in controlling waste.
If this material is used in cementing oil and gas wells, it will significantly reduce the weight of drilling mud. Gilsonite can reduce the weight of drilling fluid if added in low concentrations to the drilling mud. By increasing the concentration of this substance, the amount of weight loss in mud decreases significantly.
Use of barite in drilling pressure control
In deep oil and gas drilling by rotary method and in areas where gas or liquid pressure is high, a heavy mud is needed to control these pressures. This heavy fluid must rotate to prevent the lost circulation and control the pressure. Barite is one of the materials used in the production of drilling mud additives to control pressure. Under these conditions, barite powder is added to a normal solution of water and clay. Barite is widely used due to its weighting property, chemical neutrality and relatively cheap price.
Barite powder is added to the drilling mud to increase the density of the mud on the drill bit and thus prevent the well from eruption. Barite is used more than other drilling mud additives due to its non-corrosive, non-abrasive and insoluble properties, as well as its cheaper price. In general, the most important applications of barite in the drilling industry are standard and cost-effective weighting agents for drilling mud, increasing the density of drilling mud, cooling and lubricating the drill bit, controlling the formation pressure and strengthening the well walls.
To perform drilling operations, it is necessary to produce drilling mud in accordance with the structural of formation. Drilling mud with different characteristics is produced in different formations to control pressure, loss circulation, prevent well eruption, etc. Each of the drilling fluid additives has the ability to improve certain characteristics of the drilling fluid. Gilsonite and barite are two chemicals that can improve the properties of drilling mud. These two products are used for drilling with special formulations.