Lesson 8 Aerated Fluid drilling - PETE 689 Underbalanced...

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Unformatted text preview: PETE 689 Underbalanced Drilling UBD Lesson 8 DEA­101 Aerated Fluid Drilling Chapter 4.1 Harold Vance Department of Petroleum Engineering Definition Definition Introduction of gas into a drilling fluid for the purpose of reducing the hydrostatic head. Harold Vance Department of Petroleum Engineering Gaseated Mud Gaseated Mud Uses Control lost circulation. Avoid differential pressure sticking. Increase drilling rate. Reduce or avoid reservoir damage. Harold Vance Department of Petroleum Engineering Gaseated Mud Advantages Equivalent Mud Weight reduction down to 4ppg. Simple system. Not much can go wrong that can’t be fixed. Harold Vance Department of Petroleum Engineering Gaseated Mud Hole Problems Pressure Surges. Velocity Surges. • These can lead to hole caving and/or reservoir damage. Harold Vance Department of Petroleum Engineering Gaseated Mud Gaseated Mud Environmental Problems Large volumes of water or oil. Oil emulsifying into mud. Residual H2S in cuttings. Foaming with oil. Room on location. Harold Vance Department of Petroleum Engineering Gaseated Mud Fluid Density Range FRESH WATER FRESH WATER OIL BASE MUD OIL GASEATED MUD LWSA FOAM WITH BACK­PRESS STABLE FOAM MIST AIR, GAS 0 1 2 3 4 5 6 FLUID DENSITY (PPG) Harold Vance Department of Petroleum Engineering 7 8 9 Aerated Systems Aerated Systems Historical preference ­ drilling mud. Historical preference ­ drilling mud. Future use ­ clear fluids and mud. Future use ­ clear fluids and mud. • Diesel oil. • Other synthetic or light oils. • Water. • Water w/polymers. Harold Vance Department of Petroleum Engineering Gaseated Systems Gaseated Systems General Pressure and Volume Requirements Maximum pressure: +/­ 10,000 kPa (1,500 psi) Volume: 20­45 m3 (700­1,500 scfm) Harold Vance Department of Petroleum Engineering Annular Velocity Rules Annular Velocity Rules of Thumb for Hole Cleaning Conventional AV > 120 fpm (vertical). Conventional AV > 150 fpm (Horizontal). This should be enough to clean the bit and the bottom of the hole. Harold Vance Department of Petroleum Engineering Planning ­ Initial Volumes Planning ­ Initial Volumes Start with 2/3 the amount of mud needed for 120 ft/min annular velocity. This can be increased for horizontal wells or other problems. Harold Vance Department of Petroleum Engineering Planning ­ Initial Volumes Planning ­ Initial Volumes Start with 30 times as much air at STP as mud. 30 X (Mud gpm X 7.5) = SCF air at STP. Harold Vance Department of Petroleum Engineering Gaseated Injection Ratios Gaseated Injection Ratios 5 40 1 1 Injection ratio at STP varies. • 5 gas/1 liquid. oLess doesn’t do much good. • 40 gas/1 liquid. oMore is very unstable. Harold Vance Department of Petroleum Engineering Definition Definition Ratio ­ at surface conditions, Ratio the Ratio of gas to fluid, where fluid is expressed as 1 (e.g. 20/1) Harold Vance Department of Petroleum Engineering Definition Quality ­ The % gas in a system. Quality (This is ordinarily a foam term). This may be expressed as a %, a decimal, or as a number. Harold Vance Department of Petroleum Engineering Gaseated Injection Ratios Gaseated Injection Ratios Upper limit of stability is about 10/1 or 90% Quality at the top of the hole. Beyond that there is severe surging. Harold Vance Department of Petroleum Engineering Surface Injection Surface Injection Ratio vs. Downhole “Foam” Quality 8,000 ft Hole 9 ppg “Mud” Surface Ratio 10:1 (Gas: “Mud”) Quality: 91% at Surface ­ 3% at the bit Harold Vance Department of Petroleum Engineering Foam Quality and Mud Ratio Foam Quality and Mud Ratio Surface Based on 9 lb/gal Mud Air/Mud Ratio =10/1 Q = 91% R = 1.4/1 1000’ Q = 58% R = 0.23/1 2000’ Q = 18% R = 0.09/1 4000’ Q = 8% R = 0.05/1 R = 0.03/1 6000’ Q = 5% 8000’ Q = 3% Harold Vance Department of Petroleum Engineering Aerated Systems Aerated Systems (­) Gas causes reduction in bottom hole pressure. (+)Friction due to velocity causes addition to bottom hole pressure. Harold Vance Department of Petroleum Engineering Calculations Calculations General Gas Law P1 * V1 P2 * V2 = T1 * Z1 T2 * Z2 Harold Vance Department of Petroleum Engineering Foam Quality and Mud Ratio Foam Quality and Mud Ratio Surface Based on 9 lb/gal Mud Air/Mud Ratio =10/1 Q = 91% R = 1.4/1 1000’ Q = 58% R = 0.23/1 2000’ Q = 18% R = 0.09/1 4000’ Q = 8% R = 0.05/1 R = 0.03/1 6000’ Q = 5% 8000’ Q = 3% Harold Vance Department of Petroleum Engineering Gaseated Bottom Hole Pressure Check (more or less) ∆ p =P(circ1) ­ P(circ2) ∆ p = decrease in BHP P(circ1) = mud circulating pressure. P(circ2) = gaseated circulating pressure. Harold Vance Department of Petroleum Engineering Gaseated Bottom Hole Pressure Check (more or less) ∆ p = ∆ Vmud / (Vann x fg) ∆ Vmud = ∆ in pits in bbls Vann = Vol ann bbl/ft fg = Fluid gradient psi/ft Harold Vance Department of Petroleum Engineering Typical Volume Requirement Chart Typical Volume Requirement Chart (After Phillips Pet. Co.) Cubic Ft of Air at 14.7 Psia and 60°F Per Barrel of Mud 180 160 140 120 100 No Dynamic effects: Friction Separation Desired Fluid Weight, Ppg 80 60 40 20 Req'D. Reduction, Ppg 2.0 5.0 10 4.0 4 1,000 2,000 3,000 4,000 5,000 0 6,000 Drilling Depth in Feet 7,000 8,000 3.0 1.0 0.5 9,000 10,000 Harold Vance Department of Petroleum Engineering Aerated Systems Aerated Systems Single Biggest Problem Pressure Surges Harold Vance Department of Petroleum Engineering Aerated System Pressure Aerated System Pressure Surges Typical Bottomhole Pressure Survey Typical Bottomhole Pressure Survey During an Underbalanced Drilling During an Underbalanced Drilling Operation Operation (N2 Circulation Prior to Connections) Hydrostatic Pressure Connections/Slugs Hydrostatic Pressure Pressure Pressure Reservoir Pressure Reservoir Pressure Time Time Harold Vance Department of Petroleum Engineering Flow Regimes Flow Regimes Depend on Velocity Variations Bubble Flow Slug Flow Churn Flow Harold Vance Department of Petroleum Engineering Annular Flow Threshold Velocities for Threshold Velocities for Maintaining a Mixture of Gas and Fluid Liquid Velocity ft/sec 100 A Bubble 10 Annular B 1 C Slug 0.1 A B Churn 0.01 0.1 1 10 100 Gas Velocity ft/sec 1000 Separation of Gas and Fluid Separation of Gas and Fluid Large hole ­ low velocity • Polymer to increase viscosity. • Increase velocity as much as reasonable. Harold Vance Department of Petroleum Engineering Separation of Gas and Fluid Small hole ­ high velocity. Medium depth. Best use of gaseated systems. Harold Vance Department of Petroleum Engineering Keeping the System Together Keeping the System Together Gas retention in the mixture. • Viscosity. o Polymers. o Gel strength. • Fluid velocity. • Small bubbles. o Jet bit. o Shut blooie line on connections. Harold Vance Department of Petroleum Engineering Gas Fluid Mixing System Gas Fluid Mixing System Harold Vance Department of Petroleum Engineering Separating the Gas from the Separating the Gas from the Mud at the Surface Spin in the separator. Time. Shale shaker screen. Gentle mixing. Low viscosity. Low gel strength. Deep rather than shallow pits. Harold Vance Department of Petroleum Engineering Vertical Separator with Spin Vertical Separator with Spin Optional 3 psi Pressure Flapper Gas Gas Baffle Inlet Tangent Spin Shelf Float Linkage To Shaker or Mud Pit Outlet Valve Harold Vance Department of Petroleum Engineering Level Control Methods Methods of Controlling Surges Harold Vance Department of Petroleum Engineering Aerated System Pressure Aerated System Pressure Surges Typical Bottomhole Pressure Survey Typical Bottomhole Pressure Survey During an Underbalanced Drilling During an Underbalanced Drilling Operation Operation (N2 Circulation Prior to Connections) Hydrostatic Pressure Connections/Slugs Hydrostatic Pressure Pressure Pressure Reservoir Pressure Reservoir Pressure Time Time Harold Vance Department of Petroleum Engineering Boosting Techniques Boosting Techniques Connection Fill DP with gas. Turn off gas. Fill DP with mud to first string float. • Turn off liquid. • Make connection. • • • Harold Vance Department of Petroleum Engineering Special Downhole Equipment Special Downhole Equipment to Limit Surging Jet sub. Parasite string. Dual casing string. Dual drill pipe. Constant circulating subs. Harold Vance Department of Petroleum Engineering Jet Sub Advantages Jet Sub Advantages No preplanning or changes. Easier to start circulation. Lower pressure surges. Gas injection pressure is lower. Lowest gas use. Harold Vance Department of Petroleum Engineering Special Downhole Equipment to Limit Surging Jet sub. Parasite string. Dual casing string. Dual drill pipe. Constant circulating subs. Harold Vance Department of Petroleum Engineering Basic Concept Basic Concept Most expansion occurs above 3,000’. Below 3,000’ there is no advantage to increasing gas injection above 200 scf/bbl (ratio of 35:1). Harold Vance Department of Petroleum Engineering Advantages of Parasite String Advantages of Parasite String Avoid heads by circulating during connections and trips. Easy to get circulation started. Simple operations. Harold Vance Department of Petroleum Engineering Problems Problems With Parasite String Need to drill larger surface hole. Slows down casing running and makes it more complex. Always the possibility of smashing or plugging the string when running it. Uses more gas than a jet sub. Harold Vance Department of Petroleum Engineering Casing Spider Casing Spider Adapter For Parasite String Slot Cut for 2 1/16” Tubing 3” Harold Vance Department of Petroleum Engineering Special Downhole Equipment Special Downhole Equipment to Limit Surging Jet sub. Parasite string. Dual casing string. Dual drill pipe. Constant circulating subs. Harold Vance Department of Petroleum Engineering Wellhead Setup Wellhead Setup for Dual Casing String Harold Vance Department of Petroleum Engineering Advantages of Dual Casing Advantages of Dual Casing Minimizes the chance of crushing the string. Inner string retrieved and used again. Can be set very deep. Harold Vance Department of Petroleum Engineering Problems with a Dual String Problems with a Dual String Requires change in well head. Extra string of stream line casing. Gas volume storage will unload well. Harold Vance Department of Petroleum Engineering Special Downhole Equipment Special Downhole Equipment to Limit Surging Jet sub. Parasite string. Dual casing string. Dual drill pipe. Constant circulating subs. Harold Vance Department of Petroleum Engineering Dual Drill Pipe Dual Drill Pipe It is a mining tool and seldom used in the oil field. Harold Vance Department of Petroleum Engineering Constant Circulating Subs Constant Circulating Subs Used in the late 1960’s, no longer available. Good for connections. No advantage on trips. Lots of extra subs. Harold Vance Department of Petroleum Engineering Constant Circulating Sub Float Pins Full opening float 2” Airline 2” Airline Quick connect Tool Joint O.D. Harold Vance Department of Petroleum Engineering Fluids and Gasses Fluids and Gasses Harold Vance Department of Petroleum Engineering Gaseated Systems Gases Air Nitrogen • Cryogenic • Manufactured Natural Gas Exhaust Gas Harold Vance Department of Petroleum Engineering Gaseated Systems Gaseated Systems Clear Fluids Diesel oil. Water. Saline. Other light oils. • Mineral oils. • Synthetic oils. Harold Vance Department of Petroleum Engineering Gaseated Systems Gaseated Systems Drilling Mud Conventional gel based mud. Low lime mud. Xanthan gum mud. • • • Thixotropic (holds gas). Easily broken gel strength. (Several commercial systems available). Harold Vance Department of Petroleum Engineering Corrosion Corrosion Harold Vance Department of Petroleum Engineering Always Remember: Corrosion cannot be stopped. It can only be controlled Harold Vance Department of Petroleum Engineering Corrosion Control pH Corrosion Control pH Keep pH above 9 Steel becomes passive above pH = 11 Harold Vance Department of Petroleum Engineering Corrosion Control Don’t use air. Oxygen corrosion is the most common type of corrosion. There are other types of corrosion and scaling. Harold Vance Department of Petroleum Engineering Corrosion Inhibitors Corrosion Inhibitors Harold Vance Department of Petroleum Engineering Organo­Phosphate Esters Organo­Phosphate Esters ANIONIC Foamer compatible. Good solubility. Limited scale inhibition. Relatively high temperature. Biodegradable. Excellent oxygen control. 500­2,000 ppm concentration. Harold Vance Department of Petroleum Engineering Chromates Chromates ANIONIC Extremely soluble in water. Foamer compatible. Relatively high temperature. 200­1,200 ppm concentration. Low solids system. pH > 8 Heavy metal carcinogen. Harold Vance Department of Petroleum Engineering Nitrates Nitrates ANIONIC Foamer compatible. 60­70% chromate effectiveness. Require high pH. Require high concentration. Harold Vance Department of Petroleum Engineering Phosphates Phosphates ANIONIC Primary scale inhibitor. Foamer compatible. Raise pH to 8­12. Not sufficient by themselves. Produce calcium phosphate. scale in high calcium fluid. Harold Vance Department of Petroleum Engineering Amines Amines Cationic Effective In Mud Systems. Work Well In Gas/Air. Form Protective Film. Film Easily Penetrated by Monatomic Oxygen. Foamer Incompatible. Harold Vance Department of Petroleum Engineering Equipment for Equipment for Gaseated Systems Harold Vance Department of Petroleum Engineering Rotating Head Rotating Head Harold Vance Department of Petroleum Engineering Drill String Floats Drill String Floats Harold Vance Department of Petroleum Engineering Separators Separators Typical Closed System UBD Operation Harold Vance Department of Petroleum Engineering Simple Aerated Mud Separator Simple Aerated Mud Separator Overflow Pipe De­Aerator Mud Flow Line Harold Vance Department of Petroleum Engineering Vertical Separator with Baffles Vertical Separator with Baffles Gas to Flare Gas Gas Baffle Gas vent 14 Feet Inlet flow Mud Baffle From Choke Manifold (2,3 or 4 inlets) Mud Solids or Cleanout ~8 Fee t From Choke Manifold Harold Vance Department of Petroleum Engineering Mud to Pit Vertical Separator with Spin Vertical Separator with Spin Optional 3 psi Pressure Flapper Gas Gas Baffle Inlet Tangent Spin Shelf Float Linkage To Shaker or Mud Pit Outlet Valve Harold Vance Department of Petroleum Engineering Level Control SWACO Super Mud Gas Separator SWACO Super Mud Gas Separator Gas Out 83 Mmcf/d From Well “U” Tube Level Control Harold Vance Department of Petroleum Engineering Fluid Out 50,000 bpd Closed Separator Harold Vance Department of Petroleum Engineering Schematic of Closed Separator Schematic of Closed Separator Gas Out Gas Adjustable Partition Plate Solids Transfer Pump Oil Mud Well Effluents In Solids Harold Vance Department of Petroleum Engineering Typical Horizontal Separator Typical Horizontal Separator 9’ x 50’ (3m x 15m). 50 psi (345 kpa) wp. 5 mmcf/d and 500­600 bbls. • 141,000 m3/d and 87m3 liquid. Orifice meter run. Harold Vance Department of Petroleum Engineering Vertical Separator Vertical Separator Harold Vance Department of Petroleum Engineering Typical Vertical Separator Typical Vertical Separator 4’ x 15’ (1.3m x 3m). 500 psi (3450 kPa). 25 MMcf/d and 10,000 bbls/d (700,000 m3 gas/d and 1,590 • m3/d liquid). Orifice Meter, Level Control, Dump Valves. Harold Vance Department of Petroleum Engineering Surface Surface Equipment Closed System Harold Vance Department of Petroleum Engineering Underbalance Drilling Spread Underbalance Drilling Spread Harold Vance Department of Petroleum Engineering Gas Separation System Gas Separator Gas Separator System Ensures all fluid is degassed prior to return to the system. Harold Vance Department of Petroleum Engineering Open Skimmer Open Skimmer Oil Trap Oil Overflow Drilling Fluid/Water Solids Harold Vance Department of Petroleum Engineering Sample Catcher for Closed System Sample Catcher for Closed System (Alpine, 1996) Harold Vance Department of Petroleum Engineering Harold Vance Department of Petroleum Engineering Gaseated Drilling Techniques Gaseated Drilling Techniques Harold Vance Department of Petroleum Engineering Techniques Techniques Flowline returns do not represent downhole conditions. Harold Vance Department of Petroleum Engineering Initiating Gaseated Drilling Initiating Gaseated Drilling Unloading the Hole Start Pumping gas/mud system. When pump pressure gets too high for the air compressor, stop pumping air. Pump mud until the pressure goes back down. Harold Vance Department of Petroleum Engineering Drilling Drilling There will be alternate heads of gas and mud. Heading cycle may be as long as 5 minutes. Harold Vance Department of Petroleum Engineering Control Heading Control Heading Increase viscosity. Increase mud volume(velocity) Decrease gas. Add 2 TO 3 atm of backpressure 30 to 50 psi. Decrease bit jet size. Harold Vance Department of Petroleum Engineering Connections Connections Gas and fluid will separate. Fill the drill pipe with gas before connection. Then fill to first string float with mud to keep connection dry. Harold Vance Department of Petroleum Engineering Pressure on the Annulus Pressure on the Annulus Shut in the well on connections to keep the gas under pressure. If the well is strongly flowing, the choke may have to be left slightly open. Harold Vance Department of Petroleum Engineering Gaseated System Gaseated System Making a Trip For lost circulation (well not flowing) no problem with trip. For flowing well: • Displace clean clear fluid over reservoir and kill with a floating mud cap. • Use a deployment valve. Harold Vance Department of Petroleum Engineering Gaseated System Gaseated System Stripping is a reasonable and safe technique Planning on snubbing out the pipe light stands is a bad planning practice because of the time expense. Harold Vance Department of Petroleum Engineering After a Trip After a Trip Go to bottom and unload hole with alternate mud and gas. Working back to bottom while gassing us each zone will not be successful unless you keep the well shut and bleed a little pressure. Harold Vance Department of Petroleum Engineering End End Harold Vance Department of Petroleum Engineering ...
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