Petroleum engineering (drilling) project 2

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Class3_Fluids_HoleCleaning_SolidsControl.pdf

Drilling Engineering

Class 3

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Drilling Fluids

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Drilling Fluids

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Drilling Fluids • Purpose of Drilling Fluid

• Well Control

• Clean the Wellbore of Cuttings

• Cool the Bit

• Function Downhole Tools (PDM & Turbine Motors)

• Fluid Properties

• Rheological Properties

• HTHP

• Solids Analysis

• Electric Stability

• Water phase salinity

• Alkalinity 4

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Mud Weight/Funnel Viscosity

• The Mud Weight, MW, or fluid density, is measured in lb/gal (ppg). MW is measured with a calibrated balance.

• MW is increased by adding the mineral barite

• The Funnel Viscosity, FV, is a relative trend measured with a Marsh funnel in sec/quart

• The MW and FV trend is monitored closely and periodically by the derrickman.

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Rheological Properties

• Ratio of shear stress to shear rate

‒ Shear stress is the internal resistance of a fluid to flow at a shear rate

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Plastic Viscosity • Plastic Viscosity (cP)

• PV is the rate of change of shear stress as a function of shear rate between 300 and 600 rpm in centipoise

𝑃𝑉 = 𝜃600 − 𝜃300 • PV is related to the size, shape, and number of particles

in a moving fluid

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Yield Point

• Yield Point

• Shear stress required to initiate fluid flow

• Directly related to fluid carrying capacity

𝑌𝑃[ ൗ𝑙𝑏 100𝑓𝑡2 ] = 𝜃300 − 𝑃𝑉

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Rheological Properties

• Gel Strength

• Measure of the rigid or semi-rigid gel structure developed during periods of no flow

• Maximum measured shear stress at three rpm – Ten second gel

• After remaining static ten seconds – Ten minute gel

• After remaining static ten minutes – Thirty minutes gel

• Used in some critical drilling operations 10

HTHP Filtration

• Process of a fluid filtering through a low permeability paper filter leaving solids deposited over a 30 minute period with a pressure differential of 500 PSI and a temperature of 300°F; The build up of solid cake is measured in 64ths of an inch.

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Retort & Solids Analysis

• Retort =Oil, water and solid percent by volume

• Total Solids Percent

–Low Gravity

• Drilled Solids (2.4 - 2.8 sg)

• Commercial clays (2.6 sg)

–High Gravity

• Barite (4.2 sg)

• Hematite (5.0 sg) 12

Electric Stability

• Tests emulsion stability of fluid sample

• Measures the Voltage required to initiate conductivity

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Water Phase Salinity

• The calcium analysis results along with the chloride and water content tests, are used to calculate the WPS.

• Required to avoid water transfer and resulting swelling of formation clays

• Function of formation vertical depth, pore pressure and

salinity of the water in the shale

• Inspect the cuttings over the shakers (large sharp edged

or small like coffee grinds)

• Only needed in shales with OBM

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Advantages of an Invert Emulsion Fluid • Shale stability

• Temperature stability

• Lubricity

• Corrosion resistance

• Stuck pipe prevention

• Contaminant resistant

• Production protection

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Invert Emulsion Fluid Phases

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• Water emulsified into oil – Three phases

• oil (continuous phase) • water (discontinuous

phase) • solids (discontinuous

phase)

Emulsion

• Emulsion

‒Dispersion of one immiscible fluid into another

‒Water into oil base

‒Microscopically heterogeneous mixture

• Emulsifier

‒Surface active agent

‒Decrease interfacial tension

‒Soluble in both water and oil 17

Typical Mud Products

• Emulsifiers

• Wetting agents

• Viscosifiers

• Thinners

• Filtration reducers

• Densifiers

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Drilling Mud

• Function of Mud

• 1st means of well control

• Stabilize the wellbore

• Clean the hole

• Cool the bit and formation

• Transfer Hydraulic Horsepower HHP from mud pumps to bit

• Mud is #1 in Drilling Optimization

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Types of Drilling Fluids

• Water Based Mud: +90% water, ~$60/bbl

• Diesel Based Mud: <5% water, +$100/bbl

• Synthetic/Oil Based Mud: 50-80% water, $200/bbl

• Brine/Water

• Air

• Foam

• Synthetic and Water Based Muds are used in drilling most Horizontal Shale wells

• Synthetic Mud uses a Base Oil derived from mineral oil

• Synthetic/Oil based mud is known as an Invert Emulsion Fluid

• We will represent as SBM or OBM 20

Drilling Mud

• Mud Weight (MW)

• Typically measured in lbs/gal (ppg) with a balance

• Must be sufficient so the hydrostatic pressure will overcome the formation pressure and control the well

• Marcellus drilling uses MW from 10.0 to 13.0ppg

• A lower MW will help increase rate of penetration (ROP)

• Too high of MW will result in lost circulation and high ECD

• MW should be checked often. i.e. every 20-30min

• Keep a log of MW and monitor MW of the suction and the flowline returns

• MW[ppg] = specific gravity * 8.33ppg

• Mud Weight Equivalent (MWE) testing 21

Drilling Mud Rheology

• Funnel Viscosity (FV)

• This is a trend, not a value used for calculations

• A quick indicator when something is going on with the mud, however it will not tell you what the problem is.

• Measured in sec/qt with a Marsh Funnel

• Very sensitive to temperature: Higher temp= lower viscosity

• Rule of thumb: FV ≈ 4*MW

• FV of water is 26 sec/qt @ 68°F

• FV should be checked each time the MW is checked

• Marcellus drilling SBM is ~50-70 sec/qt

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Drilling Mud Rheology

• Plastic Viscosity PV

• Measured in centipoise (cp)

• Calculated from Viscometer lab tests 𝑃𝑉 = 𝜃600 − 𝜃300

• Measures a resistance to flow primarily caused by the amount of solids in the fluid & temperature

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Drilling Mud Rheology

• Yield Point

• Units of lb/100ft2

• Relates to attractive forces in mud (solids & liquids)

• Sensitive to temperature

• YP influences:

• Equivalent Circulating Density (ECD)

• Tripping Mud Weight

• Swab/Surge Conditions

• Hole Cleaning

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Drilling Mud Rheology

Equivalent Circulating Density (ECD)

An additional pressure on the wellbore caused by the fluid while circulating. This is due to friction in the annulus, cuttings capacity in the fluid, and fluid properties. This pressure is in addition to the hydrostatic pressure of the fluid.

𝐸𝐶𝐷[𝑝𝑝𝑔] = ∆𝑃𝑎𝑛𝑛𝑢𝑙𝑢𝑠 0.052 ∗ 𝐷

+𝑀𝑊

𝑀𝑊 = 𝑚𝑢𝑑 𝑤𝑒𝑖𝑔ℎ𝑡, 𝑝𝑝𝑔 𝐷 = 𝑑𝑒𝑝𝑡ℎ 𝑎𝑡 𝑑𝑒𝑠𝑖𝑟𝑒𝑑 𝐸𝐶𝐷 𝑐𝑎𝑙𝑐𝑢𝑙𝑎𝑡𝑖𝑜𝑛, 𝑓𝑡 ∆𝑃𝑎𝑛𝑛𝑢𝑙𝑢𝑠 = 𝑎𝑛𝑛𝑢𝑙𝑎𝑟 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑙𝑜𝑠𝑠, 𝑝𝑠𝑖

Annular ΔP is dependent on MW, YP, flow area, fluid velocity, friction factors (Re, turbulent or laminar)

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Drilling Mud Rheology

• Low Shear Yield Point (LSYP)

• Units of lb/100ft2

• Good indication of cuttings carrying capacity in horizontal wellbores

• Treat mud with a low shear modifier to increase LSYP but not impact YP

• Bio-polymers, Thixotropic, or shear thinning

• Viscosity vs. Shear Rate is inversely proportional

• There is a polymer concentration, where flow psi and suspension properties are optimized according to well conditions

𝐿𝑆𝑌𝑃 = 2𝑅3 − 𝑅6 𝑅3 = 𝐹𝑎𝑛𝑛 𝑟𝑒𝑎𝑑𝑖𝑛𝑔 @ 3𝑟𝑝𝑚 𝑅6 = 𝐹𝑎𝑛𝑛 𝑟𝑒𝑎𝑑𝑖𝑛𝑔 @ 6𝑟𝑝𝑚

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Drilling Mud Rheology

• Gel Strengths (Gels)

• Units of lb/100ft2

• Related to attractive forces in mud under static conditions

• Simulates a ‘no flow’ condition and quantifies a suspension of cuttings

• Fann 3rpm reading after static 10sec, 10min, 30min under constant temperature

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Solids Control

• Retort Analysis measures the amount of solids in mud

• Provides the following data:

• % Water, % Oil, % Solids, % LGS & HGS

• Low Gravity Solids

• Bentonite & Clays (~2.6 specific gravity)

• Drilled solids

• Can maintain a MW of 8.5 to 10 ppg

• High Gravity Solids

• Barite (~4.2 sg)

• Iron Oxide

• Maintain a MW of 9.5 to 21 ppg 28

Solids Control

• Solids Removal

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Equipment API Screen Size Micron Removed

Shale Shaker 40 381

80 234

100 178

150 105

200 74

325 44

Desander 50 to 60

Desilter 20 to 30

Centrifuge 5 to 100

Flocculation < 5

Solids Control

• Shale Shakers

• First step in the solids control process

• Receives fluid/cuttings from the flowline

• Uses API sized screens to shake fluid & cuttings. Fluid falls through the screens and is collected below in the ‘Sand Trap’ tank.

• Larger sized solids travel across the screen and fall into a container to be disposed of.

• Video

• http://www.slb.com/services/miswaco/services/solids_control.aspx

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Solids Control

• Centrifuge

• Centrifuge receives fluid containing fine particles from the ‘Sand Trap’

• Removes fine particles from fluid by creating G forces. Solids in the fluid with higher specific gravity will separate from the lighter weight fluid base.

• Cleaner fluid that exits the centrifuge is typically lighter in weight and called ‘Effluent’

• Video

• http://youtu.be/kkAaij_65Zo

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Class Problem

Building Volume- Oil Based Mud (OBM)

• Make 1,000 bbls of 12ppg OBM with OWR 75/25

• Given base oil wt. = 7.0 ppg

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Class Problem

• Oil/Water Weight (OWW) 𝑂𝑊𝑊 → 𝑉1𝑀𝑊1 + 𝑉2𝑀𝑊2 = 𝑉1 + 𝑉2 𝑀𝑊𝐹

0.75𝑏𝑏𝑙𝑠 ∗ 7.0𝑝𝑝𝑔 + 0.25𝑏𝑏𝑙 ∗ 8.33𝑝𝑝𝑔 = 0.75 + 0.25 𝑂𝑊𝑊

𝑂𝑊𝑊 = 7.33𝑝𝑝𝑔

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Class Problem

• Calculate the Oil/Water volume needed to build the 1000bbls of OBM

• Use Barite as weighting agent

• 4.2sg * 8.33ppg= 35ppg

• 35ppg * 42gal/bbl = 1470 ppb

𝑉𝑂𝑊 = 35 −𝑀𝑊𝐹 35 − 𝑂𝑊𝑊

∗ 𝑉𝐹 = 35 − 12𝑝𝑝𝑔

35 − 7.33𝑝𝑝𝑔 ∗ 1000𝑏𝑏𝑙𝑠 = 831𝑏𝑏𝑙𝑠

• Volume of Water needed

• 831*0.25 = 208 bbls of water

• Volume of Base Oil needed

• 831*0.75 = 623 bbls of base oil 34

Class Problem

• Calculate the amount of Barite needed

#𝐵𝑎𝑟 = 1470 𝑀𝑊𝐹 − 𝑂𝑊𝑊

35 −𝑀𝑊𝐹 ∗ 𝑉𝑂𝑊

#𝐵𝑎𝑟 = 1470 12 − 7.33

35 − 12 ∗ 831 = 248,032𝑙𝑏𝑠

𝐵𝑎𝑟 𝑏𝑏𝑙𝑠 = 248,032𝑙𝑏𝑠 ÷ 1470𝑝𝑝𝑏 = 169𝑏𝑏𝑙𝑠

• Check Material Balance

𝑉𝐹 = 208 + 623 + 169 = 1000𝑏𝑏𝑙𝑠 → 𝑜𝑘 35

Hole Cleaning

• Factors that influence hole cleaning

• ROP, RPM, flow rate, mud properties, inclination

• Flow rate is controlled by rig pumps and pressure

• Don’t drill faster than you can clean the hole

• Keep the fluid moving

• Spinning drill string helps ‘mix-up’ the cutting beds in high angle wellbores

• Most difficult hole to clean is between 30 and 60 degrees INC

• Periodically send sweeps/pills

• Circulate a ‘bottoms up’

• Calculate a B/U (in # of strokes) 36

Hole Cleaning

• Carrying Capacity Index (CCI)

• Used as an indicator of good hole cleaning parameters in holes less than 35deg INC

• If CCI < 1.0, expect poor hole cleaning

• If CCI > or = 1.0, expect good hole cleaning

𝐶𝐶𝐼 = 𝑀𝑊 ∗ 𝑌𝑃2 𝐴𝑉[

𝑓𝑡 𝑚𝑖𝑛

]

14,000 ∗ 𝑃𝑉

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Hole Cleaning

• Annular Cylindrical Volume

𝑉 𝑏𝑏𝑙𝑠 = 𝑑𝑜2 𝑖𝑛 − 𝑑𝑖2(𝑖𝑛)

1029.4 ∗ 𝐿(𝑓𝑡)

• Calculate a “bottoms up”, B/U, in # of strokes for the given well. *Ignore the BHA diameter difference

Hole TD = 18,000’ MD; 7250’ TVD

Last Casing String: 9-5/8” 36ppf J-55 set at 4000’

Bit Size = 8-3/4”

Drill Pipe Size = 5”

Calibrated Pump output = 0.081 bbls/stk

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