oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

gas well An oil well is a drillhole boring in Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas m ...

drilling, lost circulation occurs when

drilling fluid In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also us ...

, known commonly as "mud", flows into one or more geological formations instead of returning up the

annulus Annulus (or anulus) or annular indicates a ring- or donut-shaped area or structure. It may refer to: Human anatomy * ''Anulus fibrosus disci intervertebralis'', spinal structure * Annulus of Zinn, a.k.a. annular tendon or ''anulus tendineus com ...

. Lost circulation can be a serious problem during the

drilling Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ra ...

of an

oil well An oil well is a drillhole boring in Earth that is designed to bring petroleum oil hydrocarbons to the surface. Usually some natural gas is released as associated petroleum gas along with the oil. A well that is designed to produce only gas may ...

Consequences

The consequences of lost circulation can be as little as the loss of a few dollars of

, or as disastrous as a blowout and loss of life, so close monitoring of tanks, pits, and flow from the well, to quickly assess and control lost circulation, is taught and practiced. If the amount of fluid in the

wellbore A borehole is a narrow shaft bored in the ground, either vertically or horizontally. A borehole may be constructed for many different purposes, including the extraction of water ( drilled water well and tube well), other liquids (such as petrole ...

drops due to lost circulation (or any other reason),

hydrostatic pressure Fluid statics or hydrostatics is the branch of fluid mechanics that studies the condition of the equilibrium of a floating body and submerged body "fluids at hydrostatic equilibrium and the pressure in a fluid, or exerted by a fluid, on an imme ...

is reduced, which can allow a gas or fluid which is under a higher pressure than the reduced

to flow into the

. Another consequence of lost circulation is "dry drilling". Dry drilling occurs when fluid is completely lost from the well bore without drilling coming to a halt. The effects of dry drilling range from as minor as destroying a bit to as serious as major damage to the wellbore requiring a new well to be drilled. Dry drilling can also cause severe damage to the drill string, including snapping the pipe, or damage to the drilling rig itself.

Control

Although preferred, stopping lost circulation completely is not always possible or required. Controlled losses allow drilling to continue while keeping the

full, preventing an influx of gas or fluid into the

, known as a "kick", which can lead to a blowout. A number of options are available when lost circulation occurs, depending on the severity. Losses may be controlled by increasing the viscosity of the fluid with

bentonite Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-mon ...

and/or polymers, or with the addition of other additives, which typically include organic plant matter. Total losses can be regained through conventional use of increased viscosity and additives, or through use of unconventional methods such as pumping of large organic particles (like

kenaf Kenaf tymology: Persian ''Hibiscus cannabinus'', is a plant in the family Malvaceae also called Deccan hemp and Java jute. ''Hibiscus cannabinus'' is in the genus ''Hibiscus'' and is native to Africa, though its exact origin is unknown. The name ...

), paper, and large mica flakes with a high viscosity fluid. If total losses occur and circulation cannot be regained, several options are available, depending on the operational requirements and depth being drilled in relation to desired production geological zones. Continuing drilling while pumping

is one option, though continued drilling while pumping

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

is less costly and more often used. Sometimes the cuttings from continued drilling will aid in reducing leaks or stop losses altogether. A third option is to cement the zone where the losses occur, and to drill through the cement and continue drilling the well. This third option is very often the most cost effective if severe losses occur, as lost circulation sometimes cannot be controlled with other methods.

Additives

* There are many different types and particle sizes used as lost circulation materials (LCM). Products are both organic and synthetic man-made materials. Examples of lost circulation materials are: calcium carbonates, crushed mica, cellulosic plant particles, graphite and dolomites. Plant organic particles are usually micronized to go through a 230 mesh screen. Plant materials that have been used are kenaf, walnut hulls, peanut hulls, coconut coir, and grape

pomace Pomace ( ), or marc (; from French ''marc'' ), is the solid remains of grapes, olives, or other fruit after pressing for juice or oil. It contains the skins, pulp, seeds, and stems of the fruit. Grape pomace has traditionally been used to prod ...

. * Polymers are also sometimes used to increase the viscosity. Though these are more costly, they are more compatible with several types of fluid systems. * Additives which physically plug or seal the losses, including sawdust, flaked cellophane, and crushed or ground gypsum. * Other common and cheaper additives are shredded newspaper and cotton seed hulls. Cotton seed hulls are less preferred as they may cause wear to pump swabs and springs. Both of these are generally only used when either fresh or

salt water Saline water (more commonly known as salt water) is water that contains a high concentration of dissolved salts (mainly sodium chloride). On the United States Geological Survey (USGS) salinity scale, saline water is saltier than brackish water, ...

is being used for the drilling fluid. * When drilling in salt formations, brine is typically used, as it does not as readily dissolve salt, preventing the formation of washouts. Washouts not only contribute to loss of circulation, but can jeopardize the integrity of the wellbore itself.

Additive considerations

Several factors are considered in what additives are used: *Hole size being drilled. *

Drilling fluid In geotechnical engineering, drilling fluid, also called drilling mud, is used to aid the drilling of boreholes into the earth. Often used while drilling oil and natural gas wells and on exploration drilling rigs, drilling fluids are also us ...

in use. The additives must be compatible. *Depth of the well in regards to geological stability. *Depth of well in relation to the desired production zones. Plugging a production zone is not a desired outcome. *Drill bit nozzle sizes. If the additive(s) will not go through the drill bit, they cannot be used. *Other drill string mechanical equipment such as a mud motor or MWD tools. If the additive(s) will not go through the drill string, they cannot be used.

References

{{Reflist Drilling fluid

Consequences

Categories

Control

Additives

Additive considerations

References