wells and completions

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 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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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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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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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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Vertical well

Single reservoir layer

Cased hole

Perforated


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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

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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

wells and completions

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