Lost Circulation is the most costly mud related drilling problem, and induced fracture. Water slurry of diatomite is used as the high fluid loss squeeze slurry in the treatment of lost circulation and in decreasing fluid loss. Diatomite decreases the required time for collecting the filtrate to 1 min comparing with the international standard which recommended the filtrate should be collected maximum within 2–3 min.
Drilling fluid, or mud, may be defined as any fluid that is used in a drilling operation. A drilling fluid is circulated or pumped from the surface, down the drill string, through the bit, and back to the surface via the annulus. It is the single most important part of any earth excavation exercise, especially when drilling for oil and gas. Selection of the best fluid to meet anticipated conditions will minimize well costs and reduce the risk of catastrophes such as stuck Drill Pipe, Loss of circulation, gas kick, etc
Lost circulation is the term used to describe the condition characterized by lack of mud returning to the surface after being pumped down a well-bore. It is caused by the loss of some or the whole of the drilling fluid or mud at any depth into the natural fissures or due to high permeability of the formation or by pressure induced fractures resulting in fluid loss and there are high costs associated with replacing drilling fluids.
Many lost circulation materials are added to drilling fluids. One of the lost circulation water base mud (WBM) additives that is considered environmentally friendly is Diatomite silica. Silicates are non-toxic and are multi-functional materials that are being used in drilling mud formulations by causing changes in density, ionic strength, and charge. Diatomite silica is needed for critical drilling mud functions such as: drill-bit cooling, bit cleaning, effective cuttings removal to surface, down hole pressure control and Shale stabilization.
Diatomite can be combined with other materials such as organic fibbers to be used as a lost circulation control material in water drilling fluids. It is typically used as a rheological modifier or processing aid in a “squeeze” treatment, it has a highly permeable nature which allows it to rapidly form a plug to bridge fractures. Diatomite produce a highly porous mineral which can be used to seal wide fractures, as it will lose fluid very rapidly to provide a solid plug on which an impermeable filter cake may then form. Silica constitutes about 78–85 % of the chemical composition of the diatom frustules. Typical high fluid loss slurry contains a mixture of diatomite, bridging agents and barite suspended in either water or oil.
Almost any type of mud can be used as a carrying fluid for spotting lost circulation materials, but fluids that have extremely high filtration rates are best. Once the initial bridge forms, filtration allows the filtrate to be lost from the slurry depositing a firm filter cake within the fracture itself. This technique should be used against all types of loss zones. There are slight differences in application to these different loss zones, but the main distinction is increasing the size of the bridging agent as the loss zone becomes more severe.
