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As the well is being drilled, formation fluid flows into the wellbore and up to the surface. This is the opposite of the usual situation, where the wellbore is kept at a pressure above the formation to prevent formation fluid entering the well. In such a conventional "overbalanced" well, the invasion of fluid is considered a kick, and if the well is not shut-in it can lead to a <a href="/wiki/Blowout_(well_drilling)" title="Blowout (well drilling)">blowout</a>, a dangerous situation. In underbalanced drilling, however, there is a "<a href="/w/index.php?title=Rotating_head&action=edit&redlink=1" class="new" title="Rotating head (page does not exist)">rotating head</a>" at the surface - essentially a seal that diverts produced fluids to a separator while allowing the <a href="/wiki/Drill_string" title="Drill string">drill string</a> to continue rotating. </p><p>If the formation pressure is relatively high, using a lower density mud will reduce the well bore pressure below the pore pressure of the formation. Sometimes an inert gas is injected into the drilling mud to reduce its equivalent density and hence its <a href="/wiki/Hydrostatic_pressure" class="mw-redirect" title="Hydrostatic pressure">hydrostatic pressure</a> throughout the well depth. This gas is commonly nitrogen, as it is non-combustible and readily available, but air, reduced oxygen air, processed <a href="/wiki/Flue_gas" title="Flue gas">flue gas</a> and <a href="/wiki/Natural_gas" title="Natural gas">natural gas</a> have all been used in this fashion. </p><p><a href="/wiki/Coiled_tubing_drilling" title="Coiled tubing drilling">Coiled tubing drilling</a> (CTD) allows for continuous drilling and pumping and therefore underbalanced drilling can be utilized which can increase the <a href="/wiki/Rate_of_penetration" title="Rate of penetration">rate of penetration</a> (ROP). </p> <div class="mw-heading mw-heading2"><h2 id="Fluid_systems_used_in_underbalanced_drilling">Fluid systems used in underbalanced drilling</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Underbalanced_drilling&action=edit&section=1" title="Edit section: Fluid systems used in underbalanced drilling"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>There are several kinds of underbalanced drilling. The most common are listed below. </p> <ul><li>Dry air. This is also known as dusting. Here air compressors combined with a booster (which takes the head from the compressors and increases the pressure of the air, but does not increase the volume of air going down hole) are used and the only fluid injected into the well is a small amount of oil to reduce corrosion.</li> <li>Mist. A small amount of foaming agent (soap) is added into the flow of air. Fine particles of water and foam in an atmosphere of air bring cuttings back to the surface.</li> <li>Foam. A larger amount of foaming agent is added into the flow. Bubbles and slugs of bubbles in an atmosphere of mist bring cuttings back to the surface.</li> <li>Stable foam. An even larger amount of foaming agent is added into the flow. This is the consistency of a shaving cream.</li> <li>Airlift. Slugs and bubbles of air in a matrix of water, soap can or can not be added into the fluid flow of air.</li> <li>Aerated mud. Air or another gas is injected into the flow of drilling mud. Degassing units are required to remove air before it can be recirculated.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Advantages">Advantages</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Underbalanced_drilling&action=edit&section=2" title="Edit section: Advantages"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Under-balanced wells have several advantages over conventional drilling including: </p> <ul><li>Minimizes <a href="/w/index.php?title=Formation_damage&action=edit&redlink=1" class="new" title="Formation damage (page does not exist)">formation damage</a>. In a conventional well, <a href="/wiki/Drilling_mud" class="mw-redirect" title="Drilling mud">drilling mud</a> is forced into the formation in a process called <a href="/wiki/Drilling_fluid_invasion" title="Drilling fluid invasion">invasion</a>, which frequently causes formation damage - a decrease in the ability of the formation to transmit oil into the well-bore at a given pressure and flow rate. It may or may not be repairable. In under-balanced drilling, if the under-balanced state is maintained until the well becomes productive, invasion does not occur and formation damage can be completely avoided.</li> <li>Increases rate of penetration (ROP). With less pressure at the bottom of the well-bore, it is easier for the drill bit to cut and remove rock.</li> <li>Reduction of <a href="/wiki/Lost_circulation" title="Lost circulation">lost circulation</a>. Lost circulation is when drilling mud flows into the formation uncontrollably. Large amounts of mud can be lost before a proper <a href="/wiki/Mud_cake_(oil_and_gas)" title="Mud cake (oil and gas)">mud cake</a> forms, or the loss can continue indefinitely. If the well is drilled under-balanced, mud will not enter the formation and the problem can be avoided.</li> <li>Eliminates differential sticking. Differential sticking is when the drill pipe is pressed against the well-bore wall so that part of its circumference will see only reservoir pressure, while the rest will continue to be pushed by well-bore pressure. As a result, the pipe becomes stuck to the wall, and can require thousands of pounds of force to remove, which may prove impossible. Because the reservoir pressure is greater than the well-bore pressure in UBD, the pipe is pushed away from the walls, eliminating differential sticking.</li> <li>Reduces formation damage and water loss. Some rock formation has a reactive tendency to water. When drilling-mud is used the water in the drill mud reacts with the formation (mostly clay) and inherently causes formation damage (reduction in permeability and porosity). Use of under-balanced drilling can help prevent this.</li></ul> <div class="mw-heading mw-heading2"><h2 id="Disadvantages">Disadvantages</h2><span class="mw-editsection"><span class="mw-editsection-bracket">[</span><a href="/w/index.php?title=Underbalanced_drilling&action=edit&section=3" title="Edit section: Disadvantages"><span>edit</span></a><span class="mw-editsection-bracket">]</span></span></div> <p>Underbalanced drilling is usually more expensive than conventional drilling (when drilling a deviated well which requires <a href="/wiki/Directional_drilling" title="Directional drilling">directional drilling</a> tools), and has safety issues of its own. Technically the well is always in a blowout condition unless a heavier fluid is displaced into the well. Air drilling requires a faster up hole volume as the cuttings will fall faster down the annulus when the compressors are taken off the hole compared to having a higher viscosity fluid in the hole. Because air is compressible mud pulse telemetry measurement while drilling (MWD) tools which require an incompressible fluid can not work. Common technologies used to eliminate this problem are either electromagnetic MWD tools or wireline MWD tools. Downhole mechanics are usually more violent also because the volume of fluid going through a downhole motor or downhole hammer is greater than an equivalent fluid when drilling balanced or over balanced because of the need of higher up hole velocities. 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class="navbox-title" colspan="2"><link rel="mw-deduplicated-inline-style" href="mw-data:TemplateStyles:r1129693374"><style data-mw-deduplicate="TemplateStyles:r1239400231">.mw-parser-output .navbar{display:inline;font-size:88%;font-weight:normal}.mw-parser-output .navbar-collapse{float:left;text-align:left}.mw-parser-output .navbar-boxtext{word-spacing:0}.mw-parser-output .navbar ul{display:inline-block;white-space:nowrap;line-height:inherit}.mw-parser-output .navbar-brackets::before{margin-right:-0.125em;content:"[ "}.mw-parser-output .navbar-brackets::after{margin-left:-0.125em;content:" ]"}.mw-parser-output .navbar li{word-spacing:-0.125em}.mw-parser-output .navbar a>span,.mw-parser-output .navbar a>abbr{text-decoration:inherit}.mw-parser-output .navbar-mini abbr{font-variant:small-caps;border-bottom:none;text-decoration:none;cursor:inherit}.mw-parser-output .navbar-ct-full{font-size:114%;margin:0 7em}.mw-parser-output .navbar-ct-mini{font-size:114%;margin:0 4em}html.skin-theme-clientpref-night .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}@media(prefers-color-scheme:dark){html.skin-theme-clientpref-os .mw-parser-output .navbar li a abbr{color:var(--color-base)!important}}@media print{.mw-parser-output .navbar{display:none!important}}</style><div class="navbar plainlinks hlist navbar-mini"><ul><li class="nv-view"><a href="/wiki/Template:Petroleum_industry" title="Template:Petroleum industry"><abbr title="View this template">v</abbr></a></li><li class="nv-talk"><a href="/wiki/Template_talk:Petroleum_industry" title="Template talk:Petroleum industry"><abbr title="Discuss this template">t</abbr></a></li><li class="nv-edit"><a href="/wiki/Special:EditPage/Template:Petroleum_industry" title="Special:EditPage/Template:Petroleum industry"><abbr title="Edit this template">e</abbr></a></li></ul></div><div id="Petroleum_industry431" style="font-size:114%;margin:0 4em"><a href="/wiki/Petroleum_industry" title="Petroleum industry">Petroleum industry</a></div></th></tr><tr><td class="navbox-abovebelow" colspan="2"><div> <ul><li><a href="/wiki/Petroleum" title="Petroleum">Petroleum</a></li> <li><a href="/wiki/Primary_energy" title="Primary energy">Primary energy</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;"><a href="/wiki/Benchmark_(crude_oil)" title="Benchmark (crude oil)">Benchmarks</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Argus_Sour_Crude_Index" title="Argus Sour Crude Index">Argus Sour</a></li> <li><a href="/wiki/Bonny_Light_oil" title="Bonny Light oil">Bonny Light</a></li> <li><a href="/wiki/Brent_Crude" title="Brent Crude">Brent</a></li> <li><a href="/wiki/Dubai_Crude" title="Dubai Crude">Dubai</a></li> <li><a href="/wiki/Indian_Basket" title="Indian Basket">Indian Basket</a></li> <li><a href="/wiki/Indonesian_Crude_Price" title="Indonesian Crude Price">Indonesian</a></li> <li><a href="/wiki/Isthmus-34_Light" title="Isthmus-34 Light">Isthmus-34 Light</a></li> <li><a href="/wiki/Japan_Crude_Cocktail" title="Japan Crude Cocktail">Japan Cocktail</a></li> <li><a href="/wiki/OPEC_Reference_Basket" title="OPEC Reference Basket">OPEC Reference Basket</a></li> <li><a href="/wiki/Tapis_crude" title="Tapis crude">Tapis</a></li> <li><a href="/wiki/Urals_oil" title="Urals oil">Urals</a></li> <li><a href="/wiki/West_Texas_Intermediate" title="West Texas Intermediate">West Texas Intermediate</a></li> <li><a href="/wiki/Western_Canadian_Select" title="Western Canadian Select">Western Canadian Select</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;">Data</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left; font-weight:normal;">Natural gas</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/List_of_countries_by_natural_gas_consumption" title="List of countries by natural gas consumption">Consumption</a></li> <li><a href="/wiki/List_of_countries_by_natural_gas_production" title="List of countries by natural gas production">Production</a></li> <li><a href="/wiki/List_of_countries_by_natural_gas_proven_reserves" title="List of countries by natural gas proven reserves">Reserves</a></li> <li><a href="/wiki/List_of_countries_by_natural_gas_imports" title="List of countries by natural gas imports">Imports</a></li> <li><a href="/wiki/List_of_countries_by_natural_gas_exports" title="List of countries by natural gas exports">Exports</a></li> <li><a href="/wiki/Natural_gas_prices" title="Natural gas prices">Price</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left; font-weight:normal;">Petroleum</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/List_of_countries_by_oil_consumption" title="List of countries by oil consumption">Consumption</a></li> <li><a href="/wiki/List_of_countries_by_oil_production" title="List of countries by oil production">Production</a></li> <li><a href="/wiki/List_of_countries_by_proven_oil_reserves" title="List of countries by proven oil reserves">Reserves</a></li> <li><a href="/wiki/List_of_countries_by_oil_imports" title="List of countries by oil imports">Imports</a></li> <li><a href="/wiki/List_of_countries_by_oil_exports" title="List of countries by oil exports">Exports</a></li> <li><a href="/wiki/Posted_oil_price" title="Posted oil price">Posted oil price</a></li> <li><a href="/wiki/Price_of_oil" title="Price of oil">Price</a> <ul><li><a href="/wiki/Gasoline_and_diesel_usage_and_pricing" title="Gasoline and diesel usage and pricing">of gasoline and diesel</a></li></ul></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;"><a href="/wiki/Hydrocarbon_exploration" title="Hydrocarbon exploration">Exploration</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Core_sample" title="Core sample">Core sampling</a></li> <li><a href="/wiki/Exploration_geophysics" title="Exploration geophysics">Geophysics</a></li> <li><a href="/wiki/Integrated_asset_modelling" title="Integrated asset modelling">Integrated asset modelling</a></li> <li><a href="/wiki/Petroleum_engineering" title="Petroleum engineering">Petroleum engineering</a> <ul><li><a href="/wiki/Reservoir_simulation" title="Reservoir simulation">Reservoir simulation</a></li> <li><a href="/wiki/Reservoir_modeling" title="Reservoir modeling">Reservoir modeling</a></li></ul></li> <li><a href="/wiki/Petroleum_geology" title="Petroleum geology">Petroleum geology</a></li> <li><a href="/wiki/Petrophysics" title="Petrophysics">Petrophysics</a></li> <li><a href="/wiki/Reflection_seismology" title="Reflection seismology">Reflection seismology</a> <ul><li><a href="/wiki/Seismic_inversion" title="Seismic inversion">Seismic inversion</a></li></ul></li> <li><a href="/wiki/Seismic_source" title="Seismic source">Seismic source</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;"><a href="/wiki/Oil_well" title="Oil well">Drilling</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Blowout_(well_drilling)" title="Blowout (well drilling)">Blowout</a></li> <li><a href="/wiki/Completion_(oil_and_gas_wells)" title="Completion (oil and gas wells)">Completion</a> <ul><li><a href="/wiki/Squeeze_job" title="Squeeze job">Squeeze job</a></li></ul></li> <li><a href="/wiki/Differential_sticking" title="Differential sticking">Differential sticking</a></li> <li><a href="/wiki/Directional_drilling" title="Directional drilling">Directional drilling</a> <ul><li><a href="/wiki/Geosteering" title="Geosteering">Geosteering</a></li></ul></li> <li><a href="/wiki/Drill_stem_test" title="Drill stem test">Drill stem test</a></li> <li><a href="/wiki/Drilling_engineering" title="Drilling engineering">Drilling engineering</a></li> <li><a href="/wiki/Drilling_fluid" title="Drilling fluid">Drilling fluid</a> <ul><li><a href="/wiki/Drilling_fluid_invasion" title="Drilling fluid invasion">invasion</a></li></ul></li> <li><a href="/wiki/Lost_circulation" title="Lost circulation">Lost circulation</a></li> <li><a href="/wiki/Measurement_while_drilling" title="Measurement while drilling">Measurement</a></li> <li><a href="/wiki/Shale_oil_extraction" title="Shale oil extraction">Shale oil extraction</a> <ul><li><a href="/wiki/Fredrik_Ljungstr%C3%B6m#Shale_oil_extraction" title="Fredrik Ljungström">Ljungström method</a></li></ul></li> <li><a href="/wiki/Tracer_use_in_the_oil_industry" title="Tracer use in the oil industry">Tracers</a></li> <li><a class="mw-selflink selflink">Underbalanced drilling</a></li> <li><a href="/wiki/Well_logging" title="Well logging">Well logging</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;"><a href="/wiki/Extraction_of_petroleum" title="Extraction of petroleum">Production</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Petroleum_fiscal_regime" title="Petroleum fiscal regime">Petroleum fiscal regime</a> <ul><li><a href="/wiki/Petroleum_licensing" title="Petroleum licensing">Concessions</a></li> <li><a href="/wiki/Production_sharing_agreement" title="Production sharing agreement">Production sharing agreements</a></li></ul></li> <li><a href="/wiki/Artificial_lift" title="Artificial lift">Artificial lift</a> <ul><li><a href="/wiki/Gas_lift" title="Gas lift">Gas lift</a></li> <li><a href="/wiki/Pumpjack" title="Pumpjack">Pumpjack</a></li> <li><a href="/wiki/Submersible_pump" title="Submersible pump">Submersible pump (ESP)</a></li></ul></li> <li><a href="/wiki/Downstream_(petroleum_industry)" title="Downstream (petroleum industry)">Downstream</a></li> <li><a href="/wiki/Enhanced_oil_recovery" title="Enhanced oil recovery">Enhanced oil recovery (EOR)</a> <ul><li><a href="/wiki/Gas_reinjection" title="Gas reinjection">Gas reinjection</a></li> <li><a href="/wiki/Steam_injection_(oil_industry)" title="Steam injection (oil industry)">Steam injection</a></li></ul></li> <li><a href="/wiki/Midstream" title="Midstream">Midstream</a></li> <li><a href="/wiki/Petroleum_product" title="Petroleum product">Petroleum product</a></li> <li><a href="/wiki/Pipeline" title="Pipeline">Pipeline</a></li> <li><a href="/wiki/Oil_refinery" title="Oil refinery">Refining</a></li> <li><a href="/wiki/Upstream_(petroleum_industry)" title="Upstream (petroleum industry)">Upstream</a></li> <li><a href="/wiki/Water_injection_(oil_production)" title="Water injection (oil production)">Water injection</a></li> <li><a href="/wiki/Well_intervention" title="Well intervention">Well intervention</a></li> <li><a href="/wiki/Christmas_tree_(oil_well)" title="Christmas tree (oil well)">XT</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;"><a href="/wiki/History_of_the_petroleum_industry" title="History of the petroleum industry">History</a></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/1967_Oil_Embargo" title="1967 Oil Embargo">1967 Oil Embargo</a></li> <li><a href="/wiki/1973_oil_crisis" title="1973 oil crisis">1973 oil crisis</a></li> <li><a href="/wiki/1979_oil_crisis" title="1979 oil crisis">1979 oil crisis</a></li> <li><a href="/wiki/1980s_oil_glut" title="1980s oil glut">1980s oil glut</a></li> <li><a href="/wiki/1990_oil_price_shock" title="1990 oil price shock">1990 oil price shock</a></li> <li><a href="/wiki/2000s_energy_crisis" title="2000s energy crisis">2000s energy crisis</a></li> <li><a href="/wiki/2010s_oil_glut" title="2010s oil glut">2010s oil glut</a></li> <li><a href="/wiki/2020_Russia%E2%80%93Saudi_Arabia_oil_price_war" title="2020 Russia–Saudi Arabia oil price war">2020 Russia–Saudi Arabia oil price war</a></li> <li><a href="/wiki/Nationalization_of_oil_supplies" title="Nationalization of oil supplies">Nationalization</a></li> <li><a href="/wiki/Gas_Exporting_Countries_Forum" title="Gas Exporting Countries Forum">GECF</a></li> <li><a href="/wiki/OPEC" title="OPEC">OPEC</a></li> <li><a href="/wiki/Seven_Sisters_(oil_companies)" class="mw-redirect" title="Seven Sisters (oil companies)">Seven Sisters</a></li> <li><a href="/wiki/Standard_Oil" title="Standard Oil">Standard Oil</a></li> <li><a href="/wiki/History_of_the_petroleum_industry_in_Canada" title="History of the petroleum industry in Canada">Canada</a></li> <li><a href="/wiki/History_of_the_petroleum_industry_in_France" title="History of the petroleum industry in France">France</a></li> <li><a href="/wiki/History_of_the_oil_industry_in_India" title="History of the oil industry in India">India</a></li> <li><a href="/wiki/Petroleum_industry_in_Iraq" title="Petroleum industry in Iraq">Iraq</a></li> <li><a href="/wiki/History_of_the_petroleum_industry_in_Norway" title="History of the petroleum industry in Norway">Norway</a></li> <li><a href="/wiki/History_of_the_oil_industry_in_Saudi_Arabia" title="History of the oil industry in Saudi Arabia">Saudi Arabia</a></li> <li><a href="/wiki/History_of_the_petroleum_industry_in_the_United_States" title="History of the petroleum industry in the United States">United States</a></li> <li><a href="/wiki/History_of_the_Venezuelan_oil_industry" title="History of the Venezuelan oil industry">Venezuela</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;">Provinces<br />and fields</th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/List_of_natural_gas_fields" title="List of natural gas fields">List of natural gas fields</a></li> <li><a href="/wiki/List_of_oil_fields" title="List of oil fields">List of oil fields</a></li> <li><a href="/wiki/Caspian_Sea" title="Caspian Sea">Caspian Sea</a></li> <li><a href="/wiki/East_Midlands_Oil_Province" title="East Midlands Oil Province">East Midlands Oil Province</a></li> <li><a href="/wiki/East_Texas_Oil_Field" title="East Texas Oil Field">East Texas</a></li> <li><a href="/wiki/Gulf_of_Mexico" title="Gulf of Mexico">Gulf of Mexico</a></li> <li><a href="/wiki/Niger_Delta#Nigerian_oil" title="Niger Delta">Niger Delta</a></li> <li><a href="/wiki/North_Sea_oil" title="North Sea oil">North Sea</a></li> <li><a href="/wiki/Permian_Basin_(North_America)" title="Permian Basin (North America)">Permian Basin</a></li> <li><a href="/wiki/Persian_Gulf" title="Persian Gulf">Persian Gulf</a></li> <li><a href="/wiki/Prudhoe_Bay_Oil_Field" title="Prudhoe Bay Oil Field">Prudhoe Bay</a></li> <li><a href="/wiki/Oil_reserves_in_Russia" title="Oil reserves in Russia">Russia</a></li> <li><a href="/wiki/Oil_reserves_in_Venezuela" title="Oil reserves in Venezuela">Venezuela</a></li> <li><a href="/wiki/Western_Canadian_Sedimentary_Basin" class="mw-redirect" title="Western Canadian Sedimentary Basin">Western Canadian Sedimentary Basin</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;">Other topics</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/List_of_abbreviations_in_oil_and_gas_exploration_and_production" title="List of abbreviations in oil and gas exploration and production">Abbreviations</a></li> <li>Classification <ul><li><a href="/wiki/Sweet_crude_oil" title="Sweet crude oil">sweet oil</a></li> <li><a href="/wiki/Sour_crude_oil" title="Sour crude oil">sour oil</a></li></ul></li> <li><a href="/wiki/Oil_shale_gas" title="Oil shale gas">Oil shale gas</a></li> <li><a href="/wiki/Orphan_wells" title="Orphan wells">Orphan wells</a></li> <li><a href="/wiki/Peak_oil" title="Peak oil">Peak oil</a> <ul><li><a href="/wiki/Fossil_fuel_phase-out" title="Fossil fuel phase-out">fossil fuel phase-out</a></li> <li><a href="/wiki/Predicting_the_timing_of_peak_oil" title="Predicting the timing of peak oil">timing</a></li></ul></li> <li><a href="/wiki/Petrocurrency" title="Petrocurrency">Petrocurrency</a></li> <li><a href="/wiki/Petrodollar_recycling" title="Petrodollar recycling">Petrodollar recycling</a></li> <li><a href="/wiki/Petrofiction" title="Petrofiction">Petrofiction</a></li> <li><a href="/wiki/Shale_band" title="Shale band">Shale band</a></li> <li><a href="/wiki/Shale_gas" title="Shale gas">Shale gas</a></li> <li><a href="/wiki/Swing_producer" title="Swing producer">Swing producer</a></li> <li><a href="/wiki/Unconventional_(oil_and_gas)_reservoir" title="Unconventional (oil and gas) reservoir">Unconventional (oil and gas) reservoir</a> <ul><li><a href="/wiki/Heavy_crude_oil" title="Heavy crude oil">heavy crude</a></li> <li><a href="/wiki/Oil_sands" title="Oil sands">oil sands</a></li> <li><a href="/wiki/Oil_shale" title="Oil shale">oil shale</a></li> <li><a href="/wiki/Tight_oil" title="Tight oil">tight oil</a></li></ul></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;">Companies and<br />organisations</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Major<br /><a href="/wiki/List_of_oil_exploration_and_production_companies" title="List of oil exploration and production companies">petroleum<br />companies</a></div></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"></div><table class="nowraplinks navbox-subgroup" style="border-spacing:0"><tbody><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left; font-weight:normal;"><a href="/wiki/Big_Oil" title="Big Oil">Supermajors</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/BP" title="BP">BP</a></li> <li><a href="/wiki/Chevron_Corporation" title="Chevron Corporation">Chevron</a></li> <li><a href="/wiki/Eni" title="Eni">Eni</a></li> <li><a href="/wiki/ExxonMobil" title="ExxonMobil">ExxonMobil</a></li> <li><a href="/wiki/Shell_plc" title="Shell plc">Shell</a></li> <li><a href="/wiki/TotalEnergies" title="TotalEnergies">TotalEnergies</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left; font-weight:normal;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;"><a href="/wiki/National_oil_company" title="National oil company">National oil<br />companies</a></div></th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Abu_Dhabi_National_Oil_Company" title="Abu Dhabi National Oil Company">Abu Dhabi National Oil Company</a></li> <li><a href="/wiki/ANCAP_(Uruguay)" title="ANCAP (Uruguay)">ANCAP</a></li> <li><a href="/wiki/Bharat_Petroleum" title="Bharat Petroleum">Bharat Petroleum</a></li> <li><a href="/wiki/China_National_Offshore_Oil_Corporation" title="China National Offshore Oil Corporation">China National Offshore Oil Corporation</a></li> <li><a href="/wiki/China_National_Petroleum_Corporation" title="China National Petroleum Corporation">China National Petroleum Corporation</a></li> <li><a href="/wiki/Ecopetrol" title="Ecopetrol">Ecopetrol</a></li> <li><a href="/wiki/Equinor" title="Equinor">Equinor</a></li> <li><a href="/wiki/Gazprom" title="Gazprom">Gazprom</a></li> <li><a href="/wiki/Hindustan_Petroleum" title="Hindustan Petroleum">Hindustan Petroleum</a></li> <li><a href="/wiki/Indian_Oil_Corporation" title="Indian Oil Corporation">Indian Oil Corporation</a></li> <li><a href="/wiki/Iraq_National_Oil_Company" title="Iraq National Oil Company">Iraq National Oil Company</a></li> <li><a href="/wiki/KazMunayGas" title="KazMunayGas">KazMunayGas</a></li> <li><a href="/wiki/Kuwait_Petroleum_Corporation" title="Kuwait Petroleum Corporation">Kuwait Petroleum Corporation</a></li> <li><a href="/wiki/Grupa_Lotos" title="Grupa Lotos">Lotos</a></li> <li><a href="/wiki/Naftogaz" title="Naftogaz">Naftogaz</a></li> <li><a href="/wiki/National_Iranian_Oil_Company" title="National Iranian Oil Company">National Iranian Oil Company</a></li> <li><a href="/wiki/National_Iranian_South_Oil_Company" title="National Iranian South Oil Company">National Iranian South Oil Company</a></li> <li><a href="/wiki/NNPC_Limited" title="NNPC Limited">NNPC Limited</a></li> <li><a href="/wiki/Oil_%26_Gas_Development_Company" title="Oil & Gas Development Company">Oil & Gas Development Company</a></li> <li><a href="/wiki/Oil_and_Natural_Gas_Corporation" title="Oil and Natural Gas Corporation">Oil and Natural Gas Corporation</a></li> <li><a href="/wiki/Orlen" title="Orlen">Orlen</a></li> <li><a href="/wiki/PDVSA" title="PDVSA">PDVSA</a></li> <li><a href="/wiki/Pemex" title="Pemex">Pemex</a></li> <li><a href="/wiki/Pertamina" title="Pertamina">Pertamina</a></li> <li><a href="/wiki/Petrobangla" title="Petrobangla">Petrobangla</a></li> <li><a href="/wiki/Petrobras" title="Petrobras">Petrobras</a></li> <li><a href="/wiki/PetroChina" title="PetroChina">PetroChina</a></li> <li><a href="/wiki/Petronas" title="Petronas">Petronas</a></li> <li><a href="/wiki/Petrovietnam" title="Petrovietnam">Petrovietnam</a></li> <li><a href="/wiki/PTT_Public_Company_Limited" title="PTT Public Company Limited">PTT Public Company Limited</a></li> <li><a href="/wiki/QatarEnergy" title="QatarEnergy">QatarEnergy</a></li> <li><a href="/wiki/Rosneft" title="Rosneft">Rosneft</a></li> <li><a href="/wiki/Saudi_Aramco" title="Saudi Aramco">Saudi Aramco</a></li> <li><a href="/wiki/Sinopec" title="Sinopec">Sinopec</a></li> <li><a href="/wiki/SOCAR" title="SOCAR">SOCAR</a></li> <li><a href="/wiki/Sonangol_Group" title="Sonangol Group">Sonangol</a></li> <li><a href="/wiki/Sonatrach" title="Sonatrach">Sonatrach</a></li> <li><a href="/wiki/TPAO" title="TPAO">TPAO</a></li> <li><a href="/wiki/YPF" title="YPF">YPF</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left; font-weight:normal;"><a href="/wiki/Energy_trading" class="mw-redirect" title="Energy trading">Energy trading</a></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Enron" title="Enron">Enron</a></li> <li><a href="/wiki/Glencore" title="Glencore">Glencore</a></li> <li><a href="/wiki/Gunvor" title="Gunvor">Gunvor</a></li> <li><a href="/wiki/Mercuria" title="Mercuria">Mercuria</a></li> <li><a href="/wiki/Naftiran_Intertrade" title="Naftiran Intertrade">Naftiran Intertrade</a></li> <li><a href="/wiki/Trafigura" title="Trafigura">Trafigura</a></li> <li><a href="/wiki/Vitol" title="Vitol">Vitol</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left; font-weight:normal;">Others</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/APA_Corporation" title="APA Corporation">APA Corporation</a></li> <li><a href="/wiki/Cenovus_Energy" title="Cenovus Energy">Cenovus Energy</a></li> <li><a href="/wiki/Cepsa" title="Cepsa">Cepsa</a></li> <li><a href="/wiki/ConocoPhillips" title="ConocoPhillips">ConocoPhillips</a></li> <li><a href="/wiki/Devon_Energy" title="Devon Energy">Devon Energy</a></li> <li><a href="/wiki/Eneos_Holdings" title="Eneos Holdings">Eneos Holdings</a></li> <li><a href="/wiki/Galp_Energia" title="Galp Energia">Galp Energia</a></li> <li><a href="/wiki/Hess_Corporation" title="Hess Corporation">Hess Corporation</a></li> <li><a href="/wiki/Husky_Energy" title="Husky Energy">Husky Energy</a></li> <li><a href="/wiki/Imperial_Oil" title="Imperial Oil">Imperial Oil</a></li> <li><a href="/wiki/Lukoil" title="Lukoil">Lukoil</a></li> <li><a href="/wiki/Marathon_Oil" title="Marathon Oil">Marathon Oil</a></li> <li><a href="/wiki/Marathon_Petroleum" title="Marathon Petroleum">Marathon Petroleum</a></li> <li><a href="/wiki/Occidental_Petroleum" title="Occidental Petroleum">Occidental Petroleum</a></li> <li><a href="/wiki/OMV" title="OMV">OMV</a></li> <li><a href="/wiki/Phillips_66" title="Phillips 66">Phillips 66</a></li> <li><a href="/wiki/Port_Harcourt_Refining_Company" title="Port Harcourt Refining Company">Port Harcourt Refining Company</a></li> <li><a href="/wiki/Reliance_Industries" title="Reliance Industries">Reliance Industries</a></li> <li><a href="/wiki/Repsol" title="Repsol">Repsol</a></li> <li><a href="/wiki/Suncor_Energy" title="Suncor Energy">Suncor Energy</a></li> <li><a href="/wiki/Sunoco" title="Sunoco">Sunoco</a></li> <li><a href="/wiki/Surgutneftegas" title="Surgutneftegas">Surgutneftegas</a></li> <li><a href="/wiki/TechnipFMC" title="TechnipFMC">TechnipFMC</a></li> <li><a href="/wiki/TNK-BP" title="TNK-BP">TNK-BP</a></li> <li><a href="/wiki/Tullow_Oil" title="Tullow Oil">Tullow Oil</a></li> <li><a href="/wiki/T%C3%BCpra%C5%9F" title="Tüpraş">Tüpraş</a></li> <li><a href="/wiki/Valero_Energy" title="Valero Energy">Valero Energy</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;"><div style="display: inline-block; line-height: 1.2em; padding: .1em 0;">Major<br /><a href="/wiki/List_of_oilfield_service_companies" title="List of oilfield service companies">services<br />companies</a></div></th><td class="navbox-list-with-group navbox-list navbox-even" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/Amec_Foster_Wheeler" title="Amec Foster Wheeler">Amec Foster Wheeler</a></li> <li><a href="/wiki/Baker_Hughes" title="Baker Hughes">Baker Hughes</a></li> <li><a href="/wiki/Cameron_International" title="Cameron International">Cameron International</a></li> <li><a href="/wiki/CGG_(company)" class="mw-redirect" title="CGG (company)">CGG</a></li> <li><a href="/wiki/CH2M" title="CH2M">CH2M</a></li> <li><a href="/wiki/Chicago_Bridge_%26_Iron_Company" title="Chicago Bridge & Iron Company">Chicago Bridge & Iron Company</a></li> <li><a href="/wiki/China_Oilfield_Services" title="China Oilfield Services">China Oilfield Services</a></li> <li><a href="/wiki/Enbridge" title="Enbridge">Enbridge</a></li> <li><a href="/wiki/GE_Power" title="GE Power">GE Power</a></li> <li><a href="/wiki/Halliburton" title="Halliburton">Halliburton</a></li> <li><a href="/wiki/Nabors_Industries" title="Nabors Industries">Nabors Industries</a></li> <li><a href="/wiki/Naftiran_Intertrade" title="Naftiran Intertrade">Naftiran Intertrade</a></li> <li><a href="/wiki/NOV_Inc." title="NOV Inc.">NOV Inc.</a></li> <li><a href="/wiki/Petrofac" title="Petrofac">Petrofac</a></li> <li><a href="/wiki/Saipem" title="Saipem">Saipem</a></li> <li><a href="/wiki/Schlumberger" title="Schlumberger">Schlumberger</a></li> <li><a href="/wiki/Snam" title="Snam">Snam</a></li> <li><a href="/wiki/Subsea_7" title="Subsea 7">Subsea 7</a></li> <li><a href="/wiki/TC_Energy" title="TC Energy">TC Energy</a></li> <li><a href="/wiki/Transocean" title="Transocean">Transocean</a></li> <li><a href="/wiki/Valaris_Limited" title="Valaris Limited">Valaris Limited</a></li> <li><a href="/wiki/Weatherford_International" title="Weatherford International">Weatherford International</a></li> <li><a href="/wiki/John_Wood_Group" title="John Wood Group">John Wood Group</a></li></ul> </div></td></tr><tr><th scope="row" class="navbox-group" style="width:1%;text-align:left;">Others</th><td class="navbox-list-with-group navbox-list navbox-odd" style="width:100%;padding:0"><div style="padding:0 0.25em"> <ul><li><a href="/wiki/American_Petroleum_Institute" title="American Petroleum Institute">American Petroleum Institute</a></li> <li><a href="/wiki/Canadian_petroleum_companies" class="mw-redirect" title="Canadian petroleum companies">Canadian petroleum companies</a></li> <li><a href="/wiki/Intercontinental_Exchange_Futures" title="Intercontinental Exchange Futures">Intercontinental Exchange Futures</a></li> <li><a href="/wiki/International_Association_of_Oil_%26_Gas_Producers" title="International Association of Oil & Gas Producers">International Association of Oil & Gas Producers</a></li> <li><a href="/wiki/International_Energy_Agency" title="International Energy Agency">International Energy Agency</a></li> <li><a href="/wiki/Society_of_Petroleum_Engineers" title="Society of Petroleum Engineers">Society of Petroleum Engineers</a></li> <li><a href="/wiki/World_Petroleum_Council" class="mw-redirect" title="World Petroleum Council">World Petroleum Council</a></li></ul> </div></td></tr></tbody></table><div></div></td></tr><tr><td class="navbox-abovebelow" colspan="2" style="font-weight:bold;"><div> <ul><li><span class="noviewer" typeof="mw:File"><span title="Category"><img alt="" src="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/16px-Symbol_category_class.svg.png" decoding="async" width="16" height="16" class="mw-file-element" srcset="//upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/23px-Symbol_category_class.svg.png 1.5x, //upload.wikimedia.org/wikipedia/en/thumb/9/96/Symbol_category_class.svg/31px-Symbol_category_class.svg.png 2x" data-file-width="180" data-file-height="185" /></span></span> <a href="/wiki/Category:Petroleum_industry" title="Category:Petroleum industry">Category</a></li></ul> </div></td></tr></tbody></table></div> <p><b>References</b> </p><p>Nas, Steve, Chapter 12 Underbalanced Drilling, from Petroleum Engineering Handbook, Volume II, Editor Robert Mitchell, 2007, pages II-519 to 569. Handbook available from Society of Petroleum Engineers. <a rel="nofollow" class="external autonumber" href="http://www.spe.org">[1]</a> </p>    </div><noscript><img src="https://login.wikimedia.org/wiki/Special:CentralAutoLogin/start?useformat=desktop&type=1x1&usesul3=0" alt="" width="1" height="1" style="border: none; position: absolute;"></noscript> <div class="printfooter" data-nosnippet="">Retrieved from "<a dir="ltr" href="https://en.wikipedia.org/w/index.php?title=Underbalanced_drilling&oldid=1259368293">https://en.wikipedia.org/w/index.php?title=Underbalanced_drilling&oldid=1259368293</a>"</div></div> <div id="catlinks" class="catlinks" data-mw="interface"><div id="mw-normal-catlinks" class="mw-normal-catlinks"><a href="/wiki/Help:Category" title="Help:Category">Category</a>: <ul><li><a href="/wiki/Category:Drilling_technology" title="Category:Drilling technology">Drilling technology</a></li></ul></div><div id="mw-hidden-catlinks" class="mw-hidden-catlinks mw-hidden-cats-hidden">Hidden categories: <ul><li><a href="/wiki/Category:Articles_that_may_contain_original_research_from_December_2010" title="Category:Articles that may contain original research from December 2010">Articles that may contain original research from December 2010</a></li><li><a href="/wiki/Category:All_articles_that_may_contain_original_research" title="Category:All articles that may contain original research">All articles that may contain original research</a></li><li><a href="/wiki/Category:Articles_lacking_in-text_citations_from_February_2024" title="Category:Articles lacking in-text citations from February 2024">Articles lacking in-text citations from February 2024</a></li><li><a href="/wiki/Category:All_articles_lacking_in-text_citations" title="Category:All articles lacking in-text citations">All articles lacking in-text citations</a></li><li><a href="/wiki/Category:Articles_with_multiple_maintenance_issues" title="Category:Articles with multiple maintenance issues">Articles with multiple maintenance issues</a></li></ul></div></div> </div> </main> </div> <div class="mw-footer-container"> <footer id="footer" class="mw-footer" > <ul id="footer-info"> <li id="footer-info-lastmod"> This page was last edited on 24 November 2024, at 20:18<span class="anonymous-show"> (UTC)</span>.</li> <li id="footer-info-copyright">Text is available under the <a href="/wiki/Wikipedia:Text_of_the_Creative_Commons_Attribution-ShareAlike_4.0_International_License" title="Wikipedia:Text of the Creative Commons Attribution-ShareAlike 4.0 International License">Creative Commons Attribution-ShareAlike 4.0 License</a>; additional terms may apply. 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