Bài giảng Cơ sở kĩ thuật dầu khí - Chương 7: Well completion and stimulation

WELL COMPLETION and STIMULATION
GEOPET
Bài giảng được soạn bởi 
Bộ môn Khoan – Khai thác Dầu khí
Khoa Kỹ thuật Địa chất và Dầu khí
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Well Completion and Stimulation  2
CONTENTS
1. Basic Completion Methods
2. Completion Procedure
3. Perforating
4. Stimulation
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Well Completion and Stimulation  3
1. BASIC COMPLETION METHODS
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Well Completion and Stimulation  4
 Once the design well depth is 
reached, the formation is tested 
and evaluated. 
 To complete the production well, 
casing is installed and cemented, 
and the drilling rig is dismantled. 
 A service rig is brought in to 
perforate the production casing 
and run production tubing along 
with downhole equipments. 
 Production begins after surface 
safety equipment installation 
inished.
INTRODUCTION
30’’ CASING
20’’ CASING
13 3/8’’ CASING
7’’ LINER
RESERVOIR
SEA BED
PLATFORM
Production casing (9 5/8)
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Well Completion and Stimulation  5
WHAT IS COMPLETION?
Well completion creates a 
dependable pathway to the surface 
for the hydrocarbons.
The term ‘completion’ describes 
the assembly of downhole tubulars 
and other safety equipments that is 
required to enable the safe and 
efficient production of oil or gas 
from the well after it has been 
drilled.
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Well Completion and Stimulation  6
BASIC WELL COMPLETION TECHNOLOGY
 Each drilled wellbore awaiting completion is unique. Even nearby wells 
drilled to the same reservoir can have differencies in:
 depths, 
 formation characteristics, 
 and hole sizes
 A wide variety of equipment designs and procedures have been 
developed to provide safe, efficient conduits from subsurface 
reservoirs to the surface in different situations. 
 The ideal completion design 
 minimizes initial completion and operating costs, 
 providing for the most profitable operation of an oil or gas well over 
its entire life.
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Well Completion and Stimulation  7
Natural Completions
Natural completions are those in which little or no stimulation is required 
for production. Sandstone and carbonate systems with good permeability 
and mechanical stability are ideal for natural completions. 
Stimulated Completions
These completions are generally applied to improve the natural drainage 
patterns of hard, low-permeability formations. It is used to remove 
barriers that prevent easy passage of fluids into the wellbore.
Sand-Control Completions
Sand-control completions support the formation while allowing the flow of fluids. 
They are performed in young, unconsolidated or less mechanically competent 
sandstones.
TYPE OF COMPLETION
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Well Completion and Stimulation  8
TYPE OF COMPLETION
The design of a particular completion depends on:
1. The number and type of productive zones,
2. The expected pressures and flow rates,
3. The need to control sand production,
4. The need for artificial lift or stimulation the regulations 
governing operations in the area.
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Well Completion and Stimulation  9
WELL COMPLETION ACTIVITIES
Well completion activities include:
 Conducting well test 
 Setting production casing 
 Running production tubing along with 
downhole equipments
 Installing surface safety equipments
 Starting production flow 
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Well Completion and Stimulation  10
BASIC COMPLETION METHODS
 Once we drill to the target and evaluate our well by
 Mud analysis: density & viscosity
 Well logging (electrical, ascoustic, nuclear, etc)
 Coring: at bottomhole or sidewall
 Welltest: bottomhole pressure vs time -> reservoir properties
Next decision is whether to complete or abandon it????
 In the latter case:
 set a cement plug or plugs in the hole, 
 possibly recover whatever casing can be removed, 
 and return the drill-site to its original condition. 
 The more fortunate is one in which our well not only is productive, but 
economically justifies a completion.
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Well Completion and Stimulation  11
The next step usually involves the running of the final string of casing - the 
production string. 
The manner in which this is done determines the basic completion 
method and may follow one of several configurations: (interface between 
the wellbore & reservoir)
 the openhole completion, 
 the liner completion,
 the cased and perforated completion
• Without liner
• With liner
BASIC COMPLETION METHODS
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Well Completion and Stimulation  12
 The openhole completion: the producing formation is not isolated by 
the casing, which extends only to the top of the producing interval.
 The slotted liner completion: which is not cemented and not "tied back" 
to the surface.
BASIC COMPLETION METHODS
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Well Completion and Stimulation  13
 The cased and perforated completion
 Without liner: cementing the production casing across the 
productive interval and then perforating the casing for production
 With liner: a liner is cemented and perforated as a cased and 
perforated completion
BASIC COMPLETION METHODS
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Well Completion and Stimulation  14
 One of these configurations will be the basis for the completion design, 
which may incorporate:
 one or multiple strings of tubing: single, dual, or triple, etc
 and a variety of tubing components to facilitate production 
(production method): pumping, flowing, etc.
 from one or multiple zones: single or multiple zones
 For our purposes, a cased and perforated well with a single tubing 
string will serve to illustrate the typical completion procedure.
BASIC COMPLETION METHODS
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Well Completion and Stimulation  15
Subsea production systems are wells 
located on the sea floor, as opposed to 
at the surface. The safety equipments 
are installed underwater on the seabed.
They enable early production from 
deepwater, remote, and marginal fields.
Subsea production system offer a 
 ... y researchers realized that the fracture would close once the 
hydraulic pressure was relieved, 
 a solid material is added to the fracturing fluid to "prop" open the 
fracture. 
 Initial jobs consisted of perhaps 500 to 1000 gallons of gelled kerosene 
(napalm) as a fracturing fluid, with perhaps 1/2 lb of sand per gallon 
(Neely 1977). 
 These early fractures were assumed to be horizontal, following 
the bedding planes of the rock.
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Well Completion and Stimulation  60
FRACTURING
 Since that time, an enormous amount of research and field application 
of fracturing techniques has been carried out. 
 Theoretical mathematical models have been developed that permit 
engineers to predict the type of fracture and productivity increase that 
will result from a certain magnitude fracture treatment. 
 These calculations prevent the unnecessary use of enormous amounts 
of 
 costly fracture fluid, 
 proppant material, 
 and equipment horse power
by tailoring the treatment to the particular well.
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Well Completion and Stimulation  61
FRACTURING
 Although there is still some disagreement among theorists concerning 
the behavior of rock under stress, we now know that:
 Fracture orientation is dependent upon geologic conditions, 
 And that most fractures are vertical rather than horizontal.
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Well Completion and Stimulation  62
FRACTURING
 In order to significantly improve a well's productivity, a fracture must 
conduct fluid at a rate that is several orders of magnitude greater than 
the conductivity of the rock itself. 
 Creating a high-conductivity fracture involves
 selecting the appropriate fluid, additives, and proppant,
 determining the optimum volume of material to be pumped,
 pumping the material at the appropriate rate and pressure.
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Well Completion and Stimulation  63
FRACTURING
 Desirable features for a fracturing fluid include
 the ability to remain in the fracture and not leak off into the formation, 
 the viscosity necessary to transport the proppant into the fracture, 
 the ability to flow back into the well easily after depositing the 
proppant, 
 and low cost. 
 Water-based polymer solutions are popular, as are gel led hydrocarbons 
for water-sensitive formations. 
 A wide variety of additives are available to reduce fluid friction in piping, 
prevent fluid loss from the fracture, control contamination, and insure 
compatibility with the formation. 
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Well Completion and Stimulation  64
FRACTURING
 The standard proppant used to hold open the fracture is silica sand. 
 Sand can be crushed, however, in deep formations where fracture-
closure stresses are high. 
 In such cases sintered bauxite, zirconium oxide, or other high-
strength materials are substituted for sand. 
 The goal is to create at least a partial monolayer of proppant within the 
fracture, holding the fracture open, but not plugging it completely.
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Well Completion and Stimulation  65
FRACTURING
 High-strength proppant forms a single layer of particle that holds open 
the fracture and permits flow
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Well Completion and Stimulation  66
FRACTURING
 At the wellsite, the equipment required for a large fracturing job is 
somewhat more sophisticated than that required for an acid 
stimulation. 
 The fracturing fluid is held in tanks, where any necessary additives are 
mixed. 
 Proppant is sorted in similar containers, from which it is conveyed to 
high-rate blenders.
 Blenders combine the fracture fluid with the proppant and send the 
mixture to the pumping system.
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Well Completion and Stimulation  67
FRACTURING
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Well Completion and Stimulation  68
FRACTURING
 These blenders are critical to the fracturing procedure because, once 
the pumping process is under way, interruption of it can result in 
bridging of the proppant in the tubing or the fracture. 
 The job will fail and retreatment will be required. 
 Often, for major fracturing treatments, large volumes of fluid must be 
pumped at high pressure. This usually means that standard size pump 
trucks must be hooked up in parallel to a manifold. 
 The fluid is pumped down the tubing, drillpipe, or casing by this system 
into the formation. 
 A wellhead protector is often inserted through the Christmas tree to 
protect its interior from the abrasive, high-pressure fracturing fluid.
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Well Completion and Stimulation  69
Sand Control
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Well Completion and Stimulation  70
SAND CONTROL
 While a certain amount of sediment will always be produced along with 
formation fluids, sand control is the technology and practice of 
preventing sand flow from unconsolidated sandstone formations. 
 Such a problem is often found 
 in Tertiary sediments, 
 at shallow depths, 
 and in areas such as Nigeria, Indonesia, Trinidad, Venezuela, 
Canada, the U.S. Gulf Coast, and the Los Angeles Basin (Patton 
and Abbott 1982). 
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Well Completion and Stimulation  71
SAND CONTROL
Sand production leads to any or all of the following problems:
 Casing collapse;
 Abrasion of downhole and surface equipment;
 Reduced productivity;
 Completely plugged ("sanded-up") wells.
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Well Completion and Stimulation  72
SAND CONTROL
 Methods for controlling sand production have generally involved one of 
three approaches:
 an epoxy resin that can be injected into the formation near the 
wellbore and allowed to harden; this cements the sand grains 
together and by consolidating them prevents their movement.
 a metal screen and sand grain barrier that screens out the 
formation sand but does not inhibit fluid flow into the wellbore; or
 a combined treatment involving fracture stimulation and sand 
control, known as a “frac and pack” treatment.
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Well Completion and Stimulation  73
SAND CONTROL
 Metal wire-wrapped screens and gravel packs work in a manner 
analogous to a large crowd of people trying to leave a theatre through 
a small door. Each could pass through the door individually, but when 
several try at once they form a "bridge" that prevents those at the rear 
of the pack from moving at all. 
 In sand control, bridging methods employ wire-wrapped screens or 
slotted casing, both of which have carefully sized openings that allow 
the formation sand to be deposited against them. 
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Well Completion and Stimulation  74
SAND CONTROL
In the case of gravel packs, carefully sized 
clean sand is placed outside the screen to 
retain the formation sand at its outer edge.
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Well Completion and Stimulation  75
SAND CONTROL
 Correct sizing of both 
 the gravel pack sand 
 and the gravel pack screen 
requires knowledge of the information about formation grain size 
distribution that had been obtained from cores. 
 Guidelines have been developed to select sand and screen sizes that 
will prevent formation sand movement but not inhibit formation fluid 
flow.
 Gravel packing may be carried out in an openhole completion in which 
under-reaming has enlarged the volume of the pack to enlarge the 
hole prior to placing the gravel pack sand outside the screen by the 
reverse circulation technique.
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Well Completion and Stimulation  76
SAND CONTROL
Typical Open Hole Gravel Pack Installation Typical Cased Hole Gravel Pack Installation
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Well Completion and Stimulation  77
SAND CONTROL
 An inside gravel pack may also be accomplished in a cased and 
perforated completion. 
 Three common types of inside gravel packing are shown in 
1. Wash down, where the gravel is placed in the hole and the screen 
“washed” through it by circulating, 
2. Reverse circulation, where the sand is pumped down the annulus 
and the carrying fluid returned up the tubing, 
3. Crossover allows the sand slurry to be pumped down the tubing, 
depending on the method of sand placement.
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Well Completion and Stimulation  78
SAND CONTROL
Wash down Reverse 
circulation 
Cross over
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Well Completion and Stimulation  79
SAND CONTROL
Gravel packs require 
 There is a good bond between casing and formation, 
 The perforations be large and free of debris, 
and that the gravel pack sand is 
 Evenly placed around the screen 
 And not mixed with formation sand or dirty completion fluid.
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Well Completion and Stimulation  80
SAND CONTROL
 Sand consolidation techniques are best applied to shorter completion 
intervals. 
 Careful mixing and injecting of the plastic resins is important to prevent 
the mixture from hardening either too far into the formation from the 
wellbore or inside the casing. 
 Although some permeability is lost in this technique, no restrictions to 
flow are placed inside the casing as is the case in gravel packing. 
 This is attractive if future downhole work is anticipated and the 
wellbore may need to be cleaned out.
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Well Completion and Stimulation  81
SAND CONTROL
 “Frac and Pack” completion methods combine 
 hydraulic fracturing 
 and gravel packing into a single well treatment. 
 They are designed to create relatively short, highly conductive 
fractures in reservoirs of moderate to high permeability. 
 Frac and pack techniques have come into wide use, and in some 
areas have largely supplanted the more conventional sand control 
methods described above. 
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Well Completion and Stimulation  82
SAND CONTROL
 Areas of application include
- bypassing near-wellbore formation damage that can’t be removed 
with acid treatments.
- increasing formation support of casing in reservoirs that have 
formation compacting tendencies.
- vertically connecting productive intervals in thin, laminated sand-
shale sequences.
- Improving productivity in some low-permeability reservoirs
- alleviating problems caused by high wellbore differential pressure.
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Well Completion and Stimulation  83
SAND CONTROL
 The decision to complete a well with sand control is not always easy. 
 For example, in a formation where sand production may occur, the completion 
designer may risk the cost of a future workover in order to save the immediate 
expense of a gravel pack. 
 This may be particularly true if multiple producing zones in the well will 
require future work down hole. 
 Of course, the cost of remedial work to clean out and gravel-pack a sanded-up 
well may be much higher than if the work had been done during the original 
completion. 
 This is particularly true at some offshore locations where the cost of simply 
moving a work over rig on to a producing structure can be enormous. 
 With sand control, as with other facets of the completion procedure, decision 
making is dependent on a number of factors.
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Well Completion and Stimulation  84
Completion Components
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Well Completion and Stimulation  85
Well Head
Reservoir
Packer
Safety 
Valve
Gas Lift 
Valve
X-mas Tree
Tubing 
hanger
Production
Tubing
Perforation
Hydraulic 
Control Line
Pump Out 
Plug Sump
Oil Well After Completion
COMPLETION COMPONENTS
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Well Completion and Stimulation  86
30’’ CASING
9 5/8’’ CASING
20’’ CASING
13 3/8’’ CASING
7’’ LINER
PRODUCTION TUBING
RESEVOIR
SEA BED
PLATFORM
Only this casing
is visible 
from outside
Production casing (9 5/8)
WELL HEAD EQUIPMENT
COMPLETION COMPONENTS
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Well Completion and Stimulation  87
The parts of a downhole equipment are:
Gas Lift Valve
Safety Valve
Hydraulic Control Line
Pump Out Plug
Packer
DOWNHOLE EQUIPMENT
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Well Completion and Stimulation  88
DOWNHOLE EQUIPMENT
Packer
Packer is a device consisting of a 
sealing device, a holding or setting 
device and an inside passage for 
fluids. It expands externally to seal the 
well bore. It helps in blocking the fluids 
through the annular space between 
the pipe and the well bore wall. 
Packers use flexible, electrometric 
elements that expand. It is set 
hydraulically from the surface.
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Well Completion and Stimulation  89
DOWNHOLE EQUIPMENT
Gas Lift Valve
The gas lift valve is a device installed on a gas 
lift cylinder or mandrel. This device is used to 
control the flow of gas between the exterior and 
interior of well tubing. It consists of an inlet, 
outlet, a main valve, a main chamber and so 
on. The design of the side pocket is such that 
the components that are installed do not 
obstruct the flow of production. This enables
access to the well bore and the other 
components of completion.
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Well Completion and Stimulation  90
DOWNHOLE EQUIPMENT
Safety Valve
A safety valve is a device that is 
installed in the upper well bore to 
provide emergency closure of the 
channels that produce oil. The 
valve has a housing and a movable 
valve element that controls the flow 
of fluid in the 
well. 
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Well Completion and Stimulation  91
DOWNHOLE EQUIPMENT
Hydraulic Control Line
Hydraulic control line is a device filled with hydraulic fluid and connected 
to a hydraulic fluid source. 
Hydraulic control line is used to operate the safety valve. When the 
control line is pressurized up to a certain pressure limit, the safety valve 
opens. Its one end connects at the top of the safety valve and the other 
end to a pressurizing panel at the surface. It is lowered along with the 
safety valve while lowering the tubing string during completion.
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Well Completion and Stimulation  92
Well Head
The surface termination of a wellbore 
that incorporates facilities for installing 
casing hangers during the well 
construction phase is the well head. 
The well head is installed on top of the 
casing before starting to drill. It has 
two or three sections. Each section 
has two flanges to facilitate the 
connections at both the ends.
SURFACE CONTROL EQUIPMENTS 
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