Lost circulation is an occurrence in Formation when drilling fluids is lost into cracks during drilling or cementing operations. Lost circulation in drilling is always examined in two parts: prevention and remedial of loss. Prevention is to take all measures to prevent loss during drilling. This stage is usually done by technically examining the condition of the earth’s layers (geology) and recognizing the geographical area. Lost circulation treatment is also done by using additives appropriate to the structure of the earth’s layers and depending on the geological conditions, different materials and additives are used.
Preventing and controlling lost circulation reduces costs, reduces drilling time and facilitates the drilling process.
Causes of lost circulation in drilling
Lost circulation of drilling mud, which increases drilling time and costs, is one of the most important issues in the drilling industry. Causes of lost circulation must be prevented in advance in order not to lose money, time and human resources. Lost circulation occurs due to factors such as the difference between the pressure of the drilling column and the formation, the existence of gaps and the properties of the formation. To prevent this problem, there are various solutions such as reducing the weight of the mud, reducing the inlet flow to the formation, using lost circulation control materials and finally placing the cement pad.
In some formations, due to the low pressure of fluids inside the cavities compared to drilling mud, lost circulation occurs. In general, mud loss occurs because of geological reasons and drilling operation.
In drilling processes, by studying daily drilling reports on mud, geology and well diagramming, the causes of lost circulation are investigated. Furthermore, the values of the variables affecting loss circulation and the amount of loss were recorded from the well plotting reports and adjusted as a table. Then the graph of the amount of lost circulation and the factors affecting it in relation to the depth are drawn and the results were matched with lithological data. Then the loss areas are identified and solutions to solve this problem are presented.
The effect of drilling variables on the amount of lost circulation
By reviewing the daily drilling reports and well charting, drilling variables such as weight on bit (WOB), drill string rotation rate per minute, inlet flow to the well, drilling speed and mud weight are extracted. Graphs of these variables are plotted against the depth in the Excel environment to allow the study and comparison of results.
In the field of drilling variables, many factors can reduce or increase the lost, the most important factors are the weight on the bit, drilling speed, the amount of inlet mud current to the well and the amount of rotation of the drilling string in one minute. If the effect of these factors on lost circulation is precisely known, it is easy to control lost and even prevent severe cases. Some of these variables are directly related to the amount of mud lost circulation and some are inversely related.
Where does Lost circulation occurs?
Using information collected from different drilling depths, the depth of loss, geological conditions and the amount of loss are determined. Once the variable affecting the lost circulation of each area is identified, a suitable solution can be provided for each section.
For example, if the weight on the bit is a cause of waste, this factor must be controlled. Because more weight than usual on the bit causes the formation to break and this can even cause complete loss. At lower depths, factors such as drilling speed and weight on the drill are very effective.
Prevention of lost circulation
There are several solution to prevent and manage lost circulation, some of these are outlined below:
Control of pressures on the well
Drilling speed control
Drilling mud weight control
Use of anti-corrosion polymers
Drilling mud optimization
Putting cement plugs
Lost circulation materials
A drilling fluid is a mixture of liquids, solids, and sometimes gases that are pumped into a well. If the physical, chemical or rheological properties of drilling mud are not suitable, it affects safety and economic conditions. In the most appropriate drilling mud, they just pay attention to price. This leads to an increase in the overall cost of operations and a decrease the production.
In order to prevent drilling fluid wastage, control rheological properties and gelation, different chemical compounds are added to the drilling fluid. During the operation, the drilling mud may lose its original properties due to collisions with different layers of the earth. Therefor mud properties should be regularly controlled and the properties of the fluid to be constantly improved.
Various materials including minerals and chemicals are added to mud, which are used depending on the type of drilling, rock strength, formation type, drilling depth, gas layers and mineralogical composition of the rock. In general, drilling mud additives are used to create specific physical and chemical properties, including weight gain materials, viscosity control, filtration control, anti-corrosion, pH control, fluid waste control to Inside the formation and other chemicals that are effective in improving drilling fluid, he pointed out.
TEAM Chemicals is supplier of Gilsonite, Light Soda Ash, Calcium Chloride;and many other drilling mud additives and specialty chemicals. for more details please refer to product categories.
Intensity of lost circulation
Intensity of loss circulation for water-based drilling, oil-based drilling has different criteria. Drilling fluid lost is divided into three categories in terms of intensity: partial, medium and complete. The number of barrels lost per hour is the criterion for this division.
Water base drilling
Oil base drilling
25 to 100 barrels
10 to 30 barrels
Formation with lost circulation risk
There is risk of lost circulation in porous formations as well as formations with natural or induced gaps. In these formations loss causes an increase in costs and drilling time and decrease in the quality of drilled wells.
Mud loss usually occurs in formations with the following characteristics:
Stones with natural cracks
Stones with inductive slits
It should be noted that drilling fluid lost circulation sometimes occurs due to incorrect detection of the pressure gradient of rocks;
Fluid loss sometimes occurs due to incorrect determination of the pressure gradient of rocks. If the weight of the mud is higher than the pressure of the formation, the formation is broken and loss occurs. Such incidents can be minimized by accurate and proper well design.
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.
Corrosion is a natural affinity for metals to return to compounds before reduction. Oxygen corrosion in drilling industry is one of the most important factors in the destruction of metal pipes and equipment. Metals in nature are often in the form of compounds that are thermodynamically stable, lose their stability after reduction, and if they are again in close proximity to the natural environment, they are corroded and return to their original composition.
Corrosion is divided into wet and dry types. The wet corrosion mechanism is electrochemical. However, the dry corrosion is called solid-gas reactions at high temperatures. In the drilling industry wet corrosion is more common.
Corrosion of iron in drilling mud and other fluids are the other types of corrosion in drilling industry. The high electrical conductivity of fluid causes flow current and corrosion rate to increase.
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.
Introduction:The oil and gas industry is one of the largest and most important industries in the world, which is very important strategically and economically. With the development of environmental solutions in human societies, activities that endanger the environmental system will be seriously considered. For this reason, efforts have been made to reduce the environmental impact of drilling operations, especially in the use of drilling fluids. In this article, the management of green drilling fluid supply chain is investigated. First, the management of the green supply chain and related literature and the role of drilling fluids in the drilling process of oil and gas wells and the environmental effects of these materials if they are not controlled and monitored are stated. Then the management of green supply chain of drilling fluids is examined.
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.