Production Eng 2

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Production EngineeringProduction Engineering

Well Behavior (INFLOW PERFORMANCE)

Inflow PerformanceInflow Performance

Radial flow behaviorRadial flow behaviorVogel Inflow Performance RelationshipVogel Inflow Performance RelationshipCombined IPRsCombined IPRsGas Well IPRGas Well IPRVertical FlowVertical FlowFlow Regime & Nature of Two phase flowFlow Regime & Nature of Two phase flowChokes & Choke performanceChokes & Choke performanceWell CompletionsWell Completions

Inflow PerformanceInflow Performance

Driving force is not the reservoir pressure but the draw down - the difference in pressure between the reservoir and the wellbore. The inflow performance relationship (IPR) quantifies the flow rate from a well as a function of the draw down.

Zone of Interest in Inflow performance

Radil FlowRadil Flow

Radial flow of Oil to a well

Pressure distribution;

•Well producing at a constant flow rate.

• Inflow to the well occurs in a radial fashion and the variation in pressure with increasing radius away from the well will be a function of :

- Rock properties

- Fluid properties

- Conditions of inner and outer boundaries

of the system.

Fluid Flow in porous mediaFluid Flow in porous media

The Radial Inflow Equation for Steady State Flow

• h, re and rw are constant

• μ, and Bo are pressure dependent (possibly also k if significant compaction

Vogel Inflow Performance Relationship

IPR for a solution gas drive

Two phase liquid and gas flow occurs in the reservoir when the flowing bottom hole pressure is below the bubble point pressure.

Vogel IPRVogel IPR

Combined IPRCombined IPR

Gas Well IPRGas Well IPR

In gas wells we are faced with the problem that both fluid viscosity and compressibility are highly pressure dependent. Therefore an IPR similar to the Vogel IPR above would appear to be appropriate. However, the situation is further complicated by high flow velocities around the wellbore, which often lead to turbulent flow. The Darcy flow model assumes purely laminar flow and is not valid for the additional pressure drops caused by turbulence in gas wells.

The resulting non-linear IPR of gas wells is often expressed as:

Establishing A Well's IPR

The inflow performance relationship for a given well has to be established by a well test. In theory, one production rate with corresponding bottom hole pressure and the shut-in pressure will define the inflow performance relationship. In practice a number of flow rates may be taken to confirm the well performance. If a sample of formation fluid is taken and analysed to establish the bubble point pressure, it will be possible to decide whether to use the straight line, the Vogel or the Vogel/Glass inflow performance relationship.

Use of the IPR

The inflow performance relationship is useful as a tool to monitor well performance and predict the stimulation and artificial lift requirements of a number of wells. The IPR for a well must be known in order to size the well tubulars correctly. Based on interpolation between wells, if the initial IPR for a well is lower than expected in a particular part of the reservoir, it may then be suspected that the formation has been badly damaged during the drilling and completion phase. Mapping the IPRs across the field may highlight this situation. When wellbore damage is confirmed by a build-up survey the well may require stimulation. Even with stimulation, the inflow performance of a well will decline with falling reservoir pressure. Plotting this decline will indicate approximately when the well will have to be artificially lifted in order to maintain the required offtake rate from the field.

Vertical FlowVertical Flow

The ability to pass reservoir fluids through the tubulars is termed the vertical flow performance and it is totally dependent on the tubing size and the fluid properties. While the vertical flow of fluid in a tube is completely independent of the inflow performance of the reservoir, the two phenomenon are closely related because inflow from the reservoir and the outflow through the tubing must, obviously, be equal at the wellbore. Therefore, the capacity of the reservoir to pass fluid to the wellbore and the capacity of the tubing to pass the fluid to the surface have to be matched and be operating in equilibrium

VERTICAL FLOW

Pressure drop in oil production

In a flowing well the majority of the pressure loss can be attributed to flow in the tubing string. Typically, 75% of all the flowing pressure losses occur in the tubing, so minimising this pressure loss has a large effect in maximising the production rate from the well.

Flow Regimes

Vertical Flow Equation

Gradient curves

The Nature of Two Phase Flow

Vertical flow of Liquid and Gas

Vertical Pressure LossVertical Pressure Loss

Effect of head & friction on vertical pressure loss

Effect of Slippage & friction on vertical pressure loss

IPR and IPR and tubing Intake Pressure Curve (IPC)

Intersection of IPR and IPC

ProductionProduction

The Well HeadThe Well HeadCasing heads, (20”,13 3/8th”,7”)Tubing Head,Christmas TreeProduction Choke Size

ChokeChoke

It is normal practice to control the rate at which a well flows by installing a restriction in the wellhead. As well as technical considerations, the economic climate or local government restrictions may make it necessary to limit the offtake rate to less than the well can manage. In summary, the production rate may have to be restricted in order to: • Produce the reservoir at the most efficient rate to maximise the

economic returns. • Limit the well offtake rate to that decreed by local government. • Limit the drawdown and flow rate to prevent sand entry into the

wellbore. • Prevent the coning of water or cusping of gas, which may be caused

by producing the well at too high a rate. • Protect surface equipment from fluctuations in the production rate. • Eliminate the effect of downstream pressure variations on the

producing well.

Choke performanceChoke performance

One of the requirements of a choke is that it isolates the producing well from pressure fluctuations, which occur, downstream of the wellhead so that separator and flowline pressures do not control the well. This condition exists if the rate of flow through the choke is greater than or equal to the speed of sound in the flowing medium and is called critical flow. For single phase gas flowing through a choke, critical flow exists if the following condition applies:

Production Choke SizeProduction Choke SizeVariable/Fixed, BeanFlow Area – n/64thsDown Hole Pressure & Flow

Model of a flowing wellModel of a flowing well

Tubing SelectionTubing Selection

The method by which the optimum tubing string is selected for a well involves the calculation of the IPR and the IPC for several different sets of conditions. These are usually as follows:

• IPRs for the expected life of the field, incorporating reservoir pressure decline and changes in the PI. • IPCs for different tubing sizes, at different GORs, water cuts and/or tubing head pressures, depending on the expected performance of the reservoir. • Production requirements such as maximising initial offtake, optimising production late in field life, etc.

Completion Types Completion Types with no sand controlwith no sand control

BarefootBarefoot Slotted Linerin Open HoleSlotted Linerin Open Hole

PerforatedCased HolePerforatedCased Hole

Completion Types Completion Types with Sand Controlwith Sand Control

PrepackedScreen

ChemicalSand

Consolidation

ChemicalSand

Consolidation

ExternalGravelPack

InternalGravelPack

FracandPack

Method to increase productivity by Method to increase productivity by either reducing skin (S) or increasing either reducing skin (S) or increasing permeability -thickness (Kh)permeability -thickness (Kh)Removal of near wellbore impairment

reduces skinMore formation height may be connected

with the wellbore, showing up as an increase in Kh

What is Stimulation?What is Stimulation?

Matrix Matrix StimulationStimulation

HCl Acid - HCl Acid - used for dissolving carbonates, either in the

formation or from drilling fluids

Mud Acid (HF & HCl) - Mud Acid (HF & HCl) - used for dissolving fines, clays and sandstone

Solvents -Solvents -used for dissolving waxes and asphaltenesemulsions can be broken down with surfactants

Hydraulic FracturingHydraulic Fracturing

Fracturing is a process by which we Fracturing is a process by which we create a highly conductive flow path create a highly conductive flow path from the wellbore into the reservoirfrom the wellbore into the reservoir

How?How? Pump at high pressure Breakdown the formation Open up & propagate the

fracture Fill the fracture up with

proppant

Fracture Growth

Direction

Fracfluid

injection min

Frac half length

Single & Dual CompletionsSingle & Dual Completions

Hydraulic Control Line

Surface Controlled Subsurface Safety Valve - SCSSV

Tubing

Packer

Tailpipe

Perforations10,000’

<2,000’

9,800’

ApproximateDepths

Xmas Tree

Single StringSingle String Dual StringDual String

Open Hole CompletionsOpen Hole Completions

BarefootBarefoot

SlottedLiner

Open hole completionOpen hole completion

Cased Hole CompletionCased Hole Completion

When a well is When a well is cased offcased off, all communication , all communication with the reservoir is lost.with the reservoir is lost.

In order to regain communication, the well In order to regain communication, the well must be must be perforatedperforated..

Well Head and completion equipmentWell Head and completion equipment

X-mass treesX-mass trees

Production platformsProduction platforms

Dissolved gas drive reservoirDissolved gas drive reservoir

Gas Cap drive reservoirGas Cap drive reservoir

Water Drive reservoirWater Drive reservoir

Typical Hdrocarbon phase diagramTypical Hdrocarbon phase diagram

Production SystemProduction System

Surface Valve and well head chokeSurface Valve and well head choke

Conventional horizontal seperatorConventional horizontal seperator

Artificial LiftArtificial Lift

Why?Why?

When ?When ?

Artificial Lift methodsArtificial Lift methods

Gas LiftGas Lift

Advantages and disadvantagesAdvantages and disadvantages

Gas lift design considerationGas lift design consideration

DisadvantagesDisadvantages

Rod PumpsRod Pumps ESPESP Hudraulic PumpHudraulic Pump Gas LiftGas Lift

1.1. Friction in Friction in crooked holescrooked holes

2.2. Pump wear Pump wear with solids with solids production.production.

3.3. Free gas Free gas reduces pump reduces pump eff.eff.

4.4. Downhole Downhole corrosion corrosion inhibition inhibition difficult.difficult.

5.5. Heavy equp. Heavy equp. For offshore For offshore use.use.

1.1. Not suitable Not suitable for shallow, for shallow, low volume low volume wells. wells.

2.2. Full workover Full workover required to required to change pumpchange pump

3.3. Cable damage Cable damage during during installation.installation.

4.4. Cable Cable deteriorates at deteriorates at high temp.high temp.

5.5. Gas and solids Gas and solids intolerant.intolerant.

1.1. High surface High surface pressure.pressure.

2.2. Free gas Free gas reduces pump reduces pump eff.eff.

3.3. Power oil Power oil systems systems hazardoushazardous

4.4. High minimum High minimum Low FBHP, Low FBHP, abandonment abandonment pressure may pressure may not be not be reached.reached.

1.1. Lift gas may Lift gas may not be not be available.available.

2.2. Not suitable Not suitable for viscous for viscous crude oil.crude oil.

3.3. Casing must Casing must withstand lift withstand lift gas pressuregas pressure

4.4. High minimum High minimum Low FBHP, Low FBHP, abandonment abandonment pressure may pressure may not be reachednot be reached

Production Optimisation & (workover)

Examples :Examples : Removal of Wellbore Damage (Acidisation)Removal of Wellbore Damage (Acidisation)

Reduce Water Production (isolate water zone)Reduce Water Production (isolate water zone)

Increase Production (by adding more perforations/etc)Increase Production (by adding more perforations/etc)

Lifting Method OptimisationLifting Method Optimisation

Pressure Support to Enhance RecoveryPressure Support to Enhance Recovery

Why : to improve a well performance and/or gather some data that will increase the Understanding of well behaviour and therefore improving the field overall performance.

Production Optimisation

Optimisation Type

Inflow Outflow

Removal of reservoir Damage

Water/Gas shut-off

Additional Perforations

Screen (wws) cleaning

Bean-ups

lifting Method Optimisation. convert BP to ESP replace damaged Pump upgrade the pump

Artificial Lift ( Examples)

Sandy wellViscous OilMax flow rate = 1500 bpd

Pr < PbDeviated wellSolid productionMax flow rate = 8000 bpd

Sandy wellLight Oil

Very good FBHP with aquifar support.

Answer : PCP

Answer : GL

Answer : NO AL

Artificial Lift ( Advantages)

Gas LiftGas Lift

ESPESP

Hydraulic PumpsHydraulic Pumps

Artificial Lift selectionArtificial Lift selection

Advantages & DisadvantagesAdvantages & Disadvantages

AdvantagesAdvantages - - No volumes constraintsNo solids problemsLow costNo Deviation constraintsNo GOR limits

DisadvantagesDisadvantages

Require high pressure gas Inefficient at low production ratesLimited drawdown capabilityRequires integral casingSafety aspects of high pressure gas

Gas Lift Completion DesignGas Lift Completion Design

Outlines;Outlines;

Well Completion DesignWell Completion Design

The Integrated Production The Integrated Production SystemSystem

Inflow performance relationship Inflow performance relationship (IPR)(IPR)

Well Completion DesignWell Completion Design

The Drillers drill wells, which then have to be completed.The Drillers drill wells, which then have to be completed.

The 3 main functions of a completion are:The 3 main functions of a completion are: Connect reservoir to well & bring fluids to surface Protect the casing Safeguard the well

Also need to maximise productivity while minimising life cycle cost.Also need to maximise productivity while minimising life cycle cost.

Inflow & Outflow DesignInflow & Outflow Design

Before you look at the hardware of a completion, you need to Before you look at the hardware of a completion, you need to predict what the well will do:predict what the well will do: What will it produce? How much? What are the pressures & temperatures? How long will it produce? Will there be any changes in the lifetime of the well? What are the uncertainties?

To do this you need to consider the flow from the reservoir to the To do this you need to consider the flow from the reservoir to the well well (Inflow)(Inflow) and the flow from the bottom of the well to surface and the flow from the bottom of the well to surface (Outflow).(Outflow).

Single & Dual CompletionsSingle & Dual Completions

Hydraulic Control Line

Surface Controlled Subsurface Safety Valve - SCSSV

Tubing

Packer

Tailpipe

Perforations10,000’

<2,000’

9,800’

ApproximateDepths

Xmas Tree

Single StringSingle String Dual StringDual String

Open Hole CompletionsOpen Hole Completions

BarefootBarefoot

SlottedLiner

Perforating TechniquesPerforating Techniques

ElectricWireline

Logging Truck

Packer

Tubing

Derrick

Electric WirelineConveyedPerforatingGuns

TubingConveyedPerforating(TCP)Guns

Improve productivityImprove productivity

Artificial liftArtificial lift Some oil wells can’t flow on their own If you suck harder the well will flow faster

Sand controlSand control Can you allow sand production?

StimulationStimulation Is the formation damaged & so has productivity been impaired?

Production System;Production System;

provide provide a a conduit conduit for the flow of fluids from the for the flow of fluids from the reservoir reservoir to to the the off take point off take point atatsurfacesurface, and sometimes also from the surface to the , and sometimes also from the surface to the subsurfacesubsurface,,separate separate the produced reservoir fluids from each other,the produced reservoir fluids from each other,minimize minimize the production or the negative effects of the production or the negative effects of by-by-productsproducts,,store store the produced fluids if they cannot immediately be the produced fluids if they cannot immediately be exportedexportedmeasure measure the amounts of fluids produced and the amounts of fluids produced and control control the the production processproduction processprovide provide a part of the a part of the energy energy required to transport fluids required to transport fluids through the system.through the system.

The main functions of an oil and gas production system are to

The Integrated Production SystemThe Integrated Production System

Flowing Wells Flowing Wells Pwf > Hydrocarbon Column Pressure

Production TubingProduction TubingThe Well HeadThe Well Head

Casing Heads, Tubing Head, Christmas Tree

Initial ProductionInitial ProductionFactors Affecting ProductionFactors Affecting ProductionSkin & PISkin & PI

Wellbore Damage – Negative Acidizing - Positive

Design & complete wellsDesign & complete wells

Vertical, deviated or horizontal well?Vertical, deviated or horizontal well? Where are drilling from & to? Optimise production

Single or dual completion?Single or dual completion? How many reservoirs? Commingled or separate production?

Perforated or open holePerforated or open hole How stable is the hole? Do you need zonal isolation

Production TubingProduction Tubing Steel Pipe run with Production Packer

The Well HeadThe Well HeadCasing Heads, (20”,13 3/8th”,7”)Tubing Head,Christmas Tree

The Well HeadThe Well HeadCasing heads, (20”,13 3/8th”,7”)Tubing Head,Christmas TreeProduction Choke Size

Initial ProductionInitial ProductionPerforationTCPWireline Perforation

Production Choke SizeProduction Choke SizeVariable/Fixed, BeanFlow Area – n/64thsDown Hole Pressure & Flow

Factors Affecting ProductionFactors Affecting ProductionReservoir Fluid PropertiesPorosity & PermeabilityRock/Fluid PropertiesProduction Design CriteriaProduction History

Inflow Performance of Oil Wells (Open Hole and Cased Hole Inflow Performance of Oil Wells (Open Hole and Cased Hole Completions)Completions)A useful inflow performance indicator in oil wells is the A useful inflow performance indicator in oil wells is the productivity index (Pl) of a zone which defines the potential productivity index (Pl) of a zone which defines the potential production rate per unit of drawdown. In general the Pl will production rate per unit of drawdown. In general the Pl will remain constant over a range of production rates, i.e. a remain constant over a range of production rates, i.e. a straight line Pl relationship, as long as the flowing bottom straight line Pl relationship, as long as the flowing bottom hole pressure Pwf is greater than the bubble point pressure hole pressure Pwf is greater than the bubble point pressure Pb, i.e. in the absence of free gas. Below Pb the inflow Pb, i.e. in the absence of free gas. Below Pb the inflow performance will become rate dependent and some form of performance will become rate dependent and some form of curved IPR will generally be required to accurately describe curved IPR will generally be required to accurately describe the inflow performance. the inflow performance.

Straight Line IPRStraight Line IPR

The straight line IPR uses a constant The straight line IPR uses a constant productivity index (PI) to describe productivity index (PI) to describe stabilised flow into the wellbore, where:stabilised flow into the wellbore, where:

This relationship is satisfactory if only This relationship is satisfactory if only liquid flow occurs in the reservoir and liquid flow occurs in the reservoir and non-Darcy (rate dependent) flow effects non-Darcy (rate dependent) flow effects are negligible. are negligible.

Straight Line IPRStraight Line IPR

The stabilised flow of a slightly compressible fluid of constant The stabilised flow of a slightly compressible fluid of constant compressibility into the wellbore of a single well completed over the compressibility into the wellbore of a single well completed over the entire producing interval in a bounded radial reservoir is given by the entire producing interval in a bounded radial reservoir is given by the semi-steady state equation: semi-steady state equation:

The skin effect, s, is generally determined from transient The skin effect, s, is generally determined from transient flow analysis, The pressure drop due to skin is defined as: flow analysis, The pressure drop due to skin is defined as: Skin Skin Wellbore Damage – Negative Acidizing – Positive

The Pl relationship can be rewritten in terms of the The Pl relationship can be rewritten in terms of the drawdown, i.e: drawdown, i.e:

The conversion constant C1= 2π (Sl units) = 7.08 x 10-3 (field units)

Radial Flow SystemRadial Flow System

Average PermeabilityAverage Permeability

Production TechnologyProduction Technology

The basic elements of a production system areThe basic elements of a production system are

• • the the near-wellbore area near-wellbore area of the reservoir, i.e. a zone of several of the reservoir, i.e. a zone of several meters in radial direction around the meters in radial direction around the wells wells at the depth of the at the depth of the reservoir,reservoir,

• • the wells from the reservoir to the the wells from the reservoir to the well head well head at surface,at surface,• • the the flowlines flowlines from the well heads to the from the well heads to the surface facilitiessurface facilities,,• • the surface facilities, consisting of the surface facilities, consisting of separatorsseparators, , pumpspumps, ,

compressors compressors and other equipment for and other equipment for treatment treatment and and measurementmeasurement, and, and

• • storage tanks storage tanks and and pipelines pipelines up to the off take point or up to the off take point or sales sales pointpoint, which can e.g. be a valve at the entrance of a gas , which can e.g. be a valve at the entrance of a gas transport pipeline or the off-loading point of an oil transport pipeline or the off-loading point of an oil terminal terminal supplying tankers.supplying tankers.

Production Eng 2

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