Lost Circulation in Drilling Operation

Lost Circulation in Drilling Operation

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.

lost circulation in drilling operation

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
Chemical inhibitors
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 GilsoniteLight Soda AshCalcium 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 drillingOil base drilling
partial<25 barrels10 barrels
medium25 to 100 barrels10 to 30 barrels
Complete>100 m330 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:

Loose formations
Stones with natural cracks
Stones with inductive slits
Channel formations

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.

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Our main export materials in TEAM Company is Calcium Chloride, Soda Ash (Sodium Carbonate), Caustic Soda Flakes(Sodium Hydroxide), Hematite, Gilsonite, .

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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.

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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 used to control lost circulation in drilling formations.

Gilsonite usage in drilling fluids

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. The amount of water required is approximately one liter per three kilograms. This size should be such that it does not block the slurry ducts and is not so small that it cannot fill the joints and cracks of the formations.

Gilsonite grain size is in the range of 200-325Mesh. Because these grains have low shear strength, they break under high pressure.

Gilsonite in Cementing Oil Well

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