Constant Bottom Hole Pressure (CBHP) Flashcards
Pressure Relationships in MPD: Static vs Dynamic
Static condition:
-pump off, fluid is not moving
-BHP=Hydrostatic Pressure
=0.052 x MW (ppg) x TVD (ft)
Dynamic condition:
-pump switch on, fluid in flowing
-have added pressure due to friction
-BHP=Hydrostatic pressure + Annular Friction Pressure
Where, annular friction pressure=MD (ft) x constant
How does the PRESSURES in MPD look graphically vs DEPTH.
Individually and combined.
What happens to BHP when we start moving the fluid?
As we move the fluid, we need more force, extra pressure to move the fluid against the annular friction, hence, the BHP increased.
What is Equivalent Mud Weight (EMW)?
EMW is an alternative way of expressing PRESSURE at a CERTAIN POINT in a well
It is a MW that would give the EQUIVALENT PRESSURE AT THAT POINT in the well
EMW (ppg) = Pressure (psi) / (Depth (ft) x 0.052)
What is EMW equation?
EMW (ppg) = Hydrostatic Pressure (psi) / (TVD ft x 0.052)
What is Equivalent Circulating Density (ECD)?
It is the pressure when the pump is switch on.
It is the term to express P.hydrostatic & P.AFP as an EMW
EXTRA INFO:
ECD is the combined weight of the drilling mud and any other fluids that are circulating in the wellbore during drilling divide by the cross sectional area of the well bore.
ECD takes into account the frictional pressure drop that occurs as the drilling mud circulates.
What is ECD equation?
ECD= HP + AFP / (TVD ft x 0.052)
It is calculated to determine the pressure that is being exerted on the formation being drilled and to ensure the well is being drilled safely and efficiently
What term do we use to express P.hydrostatic as an EMW?
Equivalent Static Density (ESD)
What term do we use to express Phydrostatic + Pannular friction as an EMW?
Equivalent Circulating Density (ECD)
If we want to plot ECD & ESD using EMW on the x-axis, instead of pressure, how would it look?
If taking drilling fluid returns across an MPD choke (closed system) what happens to the pressure drop across the choke when we stop circulation to make a connection?
How can we do to solve this problem to keep constant BHP?
Draw Flow Routing — Drilling ahead in MPD
Standpipe - Mud Pump - Mud Tank - Flowmeter - MPD Choke - RCD
Draw Flow Routing —Connection during MPD -Pascal’s Law
Explain this graph:
Applying 443psi SBP will replace AFP that will be loss during connection.
How would these lines be plotted as pressure gradients, or EMW?
What is the effect of EMW at different depths?
Explain Drilling Window (or Pressure Window).
ECD modeling will depend on what factors?
Draw ESD & ECD in conventional drilling.
What is Anchor Point?
What is Surge & Swab?
Surge:
When running in BHA/casing in to the hole, the pressure increase below the BHA/casing
Swab:
When pulling out BHA/casing from the hole, the pressure decrease below the BHA/casing
How do we mitigate against Surge & Swab effects in conventional drilling operations?
By tripping the pipe at a control speed
How can MPD help to mitigate against Surge & Swab effects?
When tripping out BHA/casing, the pressure below the BHA/casing decreases, hence, surface back pressure is applied to increase the pressure to normal.
What input are needed by the MPD software to calculate Surge & Swab effects?
- Hole OD
- BHA OD
- Mud viscosity
- Flow rate
- Trip speed
What is Pipe Light?
Pipe light is when the downward forces is greater than the downward forces of the pipe
What is the normal ‘upward force’ acting on DP/BHA in all wells?
Buoyancy
What is the weight of an object in fluid?
Weight in fluid= Weight in air -
Can Pipe Light occur in conventional drilling?
Yes
What makes Pipe Light possible in MPD?
What are the surface equipment for MPD - CBHP?
What are the major equipments?
Surface equipments for MPD — CCBHP:
- Rotating Control Device (RCD)
- MPD choke
- MPD back pressure pump
- NRVs in BHA
- Flowmeter (coriolis)
-
Major Equipments:
- RCD
- MPD choke
- Flowmeter (coriolis)
What is RCD for? Main purpose?
RCD is used to close the annulus at surface, divert the return to a special flow line while allowing drill pipe to rotate
What are the 3 main variations of RCD?
Rotate & Passive (RCD - Passive)
Rotate & Active (RCD - Active)
Pressure Control Device
What is Rotation & Passive?
What is Rotation & Active?
What is PCD?
RCD operating Range vs DP RPM graph
pressure rating of the RCD decreases as the RPM of the drillpipe increases.
RCD Sealing Element — 4 types of material
• Polyurethane (200 °F)
– Performs best in SBM/OBM
– Poor resistance to hot water
– Good fatigue life, can significantly withstand more cycles of repeated stretching.
• Natural Rubber (200 °F)
– Performs best with WBM
– Can be used with some SBM/OBM
– Costs less and more effective in absorbing vibration.
• Nitrile (250 °F)
• Butyl Elastomer (300 °F)
What are the source of deformation of RCD sealing element?
• Frictional Forces
• Side Loading Due to Rig Mid-Alignment
• Chemical Deterioriation
• Seal Wear at contact due to abrasion, cut, etc caused by tool joints
• Temperature Exposure
What are the sealing element failure observed and its causes?
Sealing element observed:
• Splitting – Excessive deformation – Fatigue.
• Loss of Interference – wear
• Cut & tear caused by tool joint, bit
• Reaction to fluid used
Causes of sealing element failure:
- Hard banding
- Corroded pipe
- Miss alignment
Function of Buffer Manifold
To route flow to MPD choke manifold.
Only in deepwater operations
Function of Junk Catcher
To remove drilling cuttings in drilling mud from plugging the Coriolis Flowmeter
- Optional - if Flowmeter is at downstream of MPD choke
- Requirement - if Flowmeter is upstream of MPD choke
Function of MPD Choke Manifold and its characteristics?
- Used to apply and control back pressure at top of well
- Have 2 identical ‘arms’
- Has 1 open pipe in the middle - bypass flow/gut line/flowline - used for cementing
- protected by pressure relief valve -during surge, open & relief pressure
- during drilling normally open both chokes, but if arm A got plugged, use B and clean A
Types of MPD Choke?
- Hydraulic
- Electric
Function of Flowmeter (Coriolis)
Measures:
- Return FR (Flow out)
- Density
- Temperature
Characteristics of a Flowmeter (coriolis)
- It is placed either downstream or upstream of the MPD choke
- give accurate calculation of kick
(more accurate than TTK) - can detect dynamic kick very quick
- Effective for single fluid
- Affected by gas (>10%) - give defected reading
Flowmeter - Coriolis Principle
- If got flow, got lag vibration due to angular momentum change
Coriolis Flowmeter - Density Measurement
- If low density liquid, tension of the spring is less
- if high density, tension of the spring is more
Tension is proportional to Density
How to solve gas problem in Flowmeter?
Before gas come out across MPD choke, pinch the valve to minimize pressure. To prevent gas coming out from fluid
Non Return Valves (NRV)
Barriers in drill string
Position: above circulating sub or any potential leak paths
2 types of NRV:
- Flapper (drop ball)
- Plunger
Process Flow Diagram (PFD) and
Pipework & Instrumentation Diagram (P&ID)
PFD - simplified version of P&ID
P&ID - use in operation
What are the 5 types of MPD Drivers?
- CBHP
-narrow margin well
-well ballooning/breathing
-uncertain pressure window
-HPHT wells
-wellbore instability
-depleted/overbalance zones - PMCD
- massive losses (carbonate) - UBD
- avoiding formation damage
- tight sandstone
- reservoir characterisation
- depleted/overbalance zones - CCS
- avoid stuck pipe in drilling/connections - DGD
- shallow sections in deepwater (very low FG)
- for environmental protection
- to control BHP (riser level management)
