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7/21/2019 Wells and Completions
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Wells and CompletionsSubsea Engineering
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Topics
Well LifecycleCompletions overview
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Well Lifecycle process overview
So just where does oil come from?
Hydrocarbon deposits originate from the
remains of plants and animals.
Over millions of years the organic matter
decayed and decomposed under conditions of
extreme pressure and heat into what we know
today as hydrocarbon products.
These may be found in liquid, gaseous, and
solid form but they all consist of the same base
elements, hydrogen (~13% by weight) and
carbon (~ 87%).
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Cycle of Deposition
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The Earth beneath our feet
The extent of reservoirs is dependent on the
structure of the earths crust
Where movement of the earths
various layers along geological fault lines is
excessive then it is these layers that are
pushed into mountains and valleyscreating
conditions conducive to the formation of oilbearing rock.
The natural fault line barriers usually prevent the migration of hydrocarbon products
and encourage their accumulation.
The majority of hydrocarbon accumulations are located between the depths of 7,000
- 13,000 feet although discoveries of new hydrocarbon areas are now being found
underneath existing reservoirs at depths up to 15,000feet.
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Just how Long has it been there?
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Oil in Place
An oil reservoir should not be thought as some
underground cavern full of oil and gas at a pressure.
Usually the hydrocarbons exist within the structure of
porous rock like a sponge full of water
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How much Oil?
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Drilling Process Overview Stage 1
Geological data is
gathered and
interpreted by
geophysicists and
geologists looking at
where, when, and at
what depth there could
be hydrocarbons in
place
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Initially by using ...Seismic data
Subsurface formations are
mapped by measuring the
time taken for acoustic
pulses generated in the
earth to return to the
surface after reflection or
refraction from interfaces
between geological
formations with different
physical properties
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Drilling Process Overview Stage 3
Drilling engineers
start the process of
designing the well in
conjunction with thegeologists, reservoir
engineers and well
completion specialists
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Things like.....
Rig Selection Permits & Legislative compliance
Blow Out Prevention
Casing Design
Mud Programme Solids Control Systems
Drill Bit Options
Directional Drilling Requirements
Logging (evaluation) Programme
Completion Requirements
HS&E (Health, Safety & Environmental) Aspects
... To name but a few...
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Drilling Process Overview Stage 4
The next stage is the
construction of the
well using drillingequipment suitable for
the pressure and
hazards expected
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Well Types
Wildcat: Little or no previous drilling exploration activity in the area
Exploratory: Geological target selection based on seismic data, and
geological modeling i.e. no previous drilling in the prospective horizon
Appraisal: Delineates the reservoirs boundaries, usually drilled after
the exploratory discoveries
Producers: Drilling into a known reservoir
Infill: Drilling in known productive portions of the reservoir that have
not been properly drained. This is usually done later in the life of the
reservoir
Re-entry: Existing well re-entered to deepen, side-track, complete, or
re-complete
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Others Include..
Step out - usually from an existing borehole,
but is used to probe for reservoir boundaries
Injector: -producing wells are often reversed in toinjectors to maintain reservoir pressure - water, gas or
steam are injected to flood the oil and gas toward the
designated producer.
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Drill Bits are used to cut / crush the rock
Roller Cone
PDC
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Drill Bits Cont
Roller cone - so called because each of the three cones rotate
independently , running on ball / race bearings or journal type
friction bearings. Cutting action is by digging or crushing the
rock
PDC means Polycrystalline Diamond Compacts - wafers of
man made diamonds used to shear the formation.
Natural diamond on a solid steel mould - used for very hardformations
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The Bottom Hole Assembly - BHA
Basic elements only - things like motors, MWD, LWD,
Jars also form part of the BHA
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Drilling Fluids Mud
Cool and lubricate the bit, drill string, and to clean the bottom of the hole
Carry cuttings to surface
Remove cuttings from the mud at surface minimize possible subsequent
formation damage Control formation pressures and to maintain hole integrity
Assist in well logging operations
Minimize corrosion of the drill string, casing and tubing, minimize
contamination problems
Minimize torque, drag and pipe sticking propensities, improve drilling rate
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Drilling Fluids Mud
A complete and
comprehensive mud plan
must be included in the
well planning process.
The drilling fluid programme must be designed to satisfy the
highest priority requirements for drilling the prospective well,
especially well control
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Drilling Fluids Mud
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Casing
Protects the newly drilled hole
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Casing - Facts
Casing strings are usually cemented in the hole to isolate the troublesome
zones behind the casing from deeper formations to be drilled
It is also used to isolate high-pressure formations below the casing from
the weaker shallower ones
Cement is normally placed behind the casing in a single or multiple stagetechnique. The single stage pumps cement down the casing and up the annulus
To stop the cement Utubing a backpressure valve is fitted at the bottom of
the casing. It is drilled out after the cement has hardened.
Liners are cemented in a slightly different fashion as they are usually run on
the end of drill pipe. The cement slurry has to run through the pipe prior to
entering the liner annular space
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Casing More Facts
Casing setting depths are directly affected by geological conditions. In some cases,
the prime criterion for selecting casing seats is to cover exposed,
severe lost circulation zones
In others, the seat selection may be based on differential sticking problems, perhaps
resulting from pressure reduction in the field
In deep wells, however the primary consideration is usually based on controllingabnormal formation pressures and preventing the exposure to weaker shallow zones.
Selecting casing seat depths for
pressure control purposes starts
with knowing geological conditionssuch as formation pressure and
fracture gradients.
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Main Functions of the Casing String
Consolidate unstable formations that have just been drilled through
Contain any pressures that may be encountered
Separate any different pressure regimes
Provide structural support for the BOPs and diverters
Protect sensitive formations from contamination
Provide a suitable environment for installation of production or
testing equipment such as packers, downhole valves, tubing, liner
hangers etc.
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Completing the Well
When a well has been
drilled and cased it
must now be
Completed in orderto produce the
hydrocarbons residing
in the reservoir
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Completing the Well - Facts
The Christmas tree provides connection and isolation between the wellbore andproduction equipment. There are usually automatic valves fitted that are fail safe i.e.
master valve and wing valve with hydraulic cylinders to open them and springs to
close them
The automatic valves, including the downhole safety valve, are usually connected to
the platform or control point ESD system
Flow string systems are the components used in the tubing string to conduct
produced fluids from the reservoir to the surface. They can include tubing, mandrels
and nipples, flow couplings, sliding sleeves, side mandrel pockets for gas lift valves
and backpressure valves
Packers provide the annular seal between the tubing and the production casing. They
must be able to withstand high differential pressures and still maintain an effective
seal
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Completing the Well - Facts
Choosing the proper size of flow string can
affect reservoir performance to some
degree
The tubing string should be sized to allow
for optimum production with a minimum
tubing size.
Since this pressure is the driving energy that
forces fluids out of the reservoir any
wasteful source of pressure dissipation can
cause lower primary reservoir recovery
Well completions involve placing flow
control equipment at the surface and in the
tubing string.
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Drilling Process Overview Stage 5
Once the well has been completed
and is flowing for commercial
purposes, it has to be maintained
with occasional intervention work for
replacement of worn parts e.g.
leaking down-hole safety
valves, and to gather pressure and
Temperature information for
reservoir management
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Post DrillingProduced Oil can be processed and stored ready for tankering in Floating Production,
Storage and Offloading (FPSO) Vessels
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Subsea pipelines can be used for transportation
Post Drilling Cont
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Monitoring
Detailed reservoir
models and simulations are
constantly updated as new
development drilling data
becomes available enabling
effective Field Management
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Drilling Process Overview Stage 6
Abandonment - this is the
stage when the reservoir is
depleted and seabed or land
is returned to its natural
environment
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General structure of an Oil company
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How a drilling contractor is structured
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Drilling Service Companies
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Topics
Well LifecycleCompletions overview
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Objectives of a Completions
To establish a safe, efficient and effective connection between the
reservoir so that hydrocarbons can be produced
Definition of the objective is affected by:
Purpose/use of the well (producer, injector..)
Environmental constraints (regulation, location..)
Drilling results (casing sizes, depth, deviation..)
Reservoir properties (pressure, temperature..)
Operational issues (completion method, equipment..)
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Completion Components
Upper completion
Across the well path but the reservoir section
Lower completion
Across the reservoir interval
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Completion Components
Vertical well
Single reservoir layer
Cased hole
Perforated
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Completion Components
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Reservoir considerations in Completiondesign
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Reservoir Drive Mechanisms
The energythat moves crude oil and natural gas from the subsurface
rock to the production well is called the reservoir drive. There are two
types of drive mechanism:
Natural drive Utilizes reservoir energy
Artificial drive Utilizes additional sources of energy
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Natural Drive Mechanisms
Three main mechanisms
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Artificial Drive Mechanisms
Water injection
Steam injection
Chemical injection
Miscible gas injection
Water Injection
C i f R i D i
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Comparism of Reservoir DriveMechanisms
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Reservoir & Well Types
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Lower Completions
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What is the Lower Completion andwhat are its main functions ?
It is the interface between the reservoir and the wellbore
It must allow effective communication between the
reservoir and the well
It must address the specific reservoir requirements such
as sand control or selectivity
It must allow whenever possible access to the reservoir
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Types of Lower Completions
Classification is not well defined but we can divide them
into:
1. Open hole
2. Cased and Perforated
Sometimes sand control are also considered a type
of lower completion
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Open Hole
Maximum productivity
Single reservoir
Lacks casing support
No selectivity of inflow
Difficult to control gas
and/or water influx
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Cased and Perforated
Impaired productivity
Multiple reservoirs
Mechanical support Selective inflow
Isolation
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Upper Completions
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What is the Upper Completion andwhat are its main functions ?
The upper completion must provide a safe and efficient path for the
hydrocarbons to flow from the wellbore to surface
It must contain and control the fluids through the life of the well
It must transport the hydrocarbons using as little energy as possible
Provide communication between the tubing and the annular side
if required
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Types of Upper Completions
Many different types are described in the literature, can be
classified in two main groups:
Single zone reservoirs
Multiple reservoirs or multiple zone reservoirs
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Single Zone Completions
l l
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Single Zone Completions
MAIN FEATURES
Through tubing perforating possible
Packer can be set with the tree in place
Fully/partially retrievable completion
Reservoir section can be left isolated and tubing retrieved
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Multiple Zone Completions
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Multiple Zone Completions
MAIN FEATURES
Separate or commingled production
Retrieval of a tubing string is possible without having to remove the
next interval completion
Through tubing perforating is possible
Up to 6 zones have been produced with multiple zone completions
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Completions a safe and efficient link between the reservoir and the production
facilities
Affected by regulation, environmental issues, drilling, reservoir characteristics,
well type
Design process is composed of:
Objectives & design criteria
Determine reservoir & well deliverability
Conceptual design & strategy
Detailed design, Planning, preparation (procurement..)
Installation, Test & Evaluation
It has two main elements: Upper & Lower completion
Summary