BÀI GIẢNG MÔN HOÀN THIỆN GIẾNG

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.

WELL COMPLETION and STIMULATION

Bài giảng được soạn bởi

Bộ môn Khoan – Khai thác Dầu khí

Khoa Kỹ thuật Địa chất và Dầu khí

1 BASIC COMPLETION METHODS

 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

INTRODUCTION

30’’ CASING 20’’ CASING

13 3/8’’ CASING

7’’ LINER

RESERVOIR

SEA BED PLATFORM

Production casing (9 5/8)

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

BASIC WELL COMPLETION TECHNOLOGY

 Each drilled wellbore awaiting completion is unique Even nearby wells drilled to the same reservoir can have differencies in:

 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

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

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.

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

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 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

 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

 The cased and perforated completion

 Without liner: cementing the production casing across the productive interval and then perforating the casing for

 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

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 means

of producing field extremities not

reachable by directional drilling from

existing platforms, or where field

economics do not justify the installation

SUBSEA COMPLETION

2 COMPLETION PROCEDURE

COMPLETION PROCEDURE

 After the contract casing crew runs the final casing, cementing follows the usual procedure , although stage cementing may be necessary to cement an extremely long string

 The production string has been hauled out to the location and the inside diameter checked to make sure that imperfections will not prevent the subsequent running in of tubing and packers after the string is set

 Special care: to prevent the possibility of future leaks

 If stage cementing is necessary:

 the bottom section is first cemented in place and then

 a series of plugs are pumped down the casing to open ports that allow the upper end of the annulus to receive cement

 After the cement has set, the inside of the casing must be

 drilled out and

 flushed clean of cement and other debris to a depth below that

of the proposed completion

It is important that the inside diameter of the production

COMPLETION PROCEDURE

COMPLETION PROCEDURE

It is also important that the cement

form a competent seal between the

casing and borehole over the entire

openhole interval To ensure this,

 an acoustic cement bond log is

sometimes run on wireline

 to determine if voids exist

between casing and hole because cement has bypassed the drilling fluid.

COMPLETION PROCEDURE

 If the bond is poor in an area, particularly if the area is between

productive formations, a cement squeeze will be required

 Often the cement bond log is run in conjunction with a gamma ray log and a casing collar log The drilling engineers can correlate this gamma ray log with the logs run earlier during formation logging

 This correlation is important because as we zero in on the target -

the productive formation - our need to locate tools precisely relative to that formation is critical

⇒ The open hole logging sondes are subjected to a greater amount

of "drag" when being pulled up the hole, the depths at which

COMPLETION PROCEDURE

 If we were to perforate the casing according to the openhole log depths, we might miss the formation entirely By using the

correlation log and casing collar log to set packers and perforate,

we are assured of precise placement

 At this point, many operators

 move the drilling rig off location and

 replace it with a less expensive, and often less powerful, completion rig

⇒ This gives the operator time to design the rest of the completion, provide for a sales contract, and order equipment.

 The casing may also be pressure tested,

 and a filtered completion fluid may be circulated into the well to displace the drilling mud prior to perforating

 This fluid is usually a heavy brine, because it:

o provides the hydrostatic pressure needed to control the well,

COMPLETION PROCEDURE

 If perforating is to be done at this point ,

 the tubing is removed and

 the perforating gun is lowered and positioned according to the correlation log and casing collars

 It is critical that the gun be placed precisely ;

 once inaccurate perforations are made, they can only be plugged off with a costly cement "squeeze."

COMPLETION PROCEDURE

 With the well perforated , it may now be time to stimulate the well

by either

 acidizing or

 hydraulically fracturing the formation.

 Acid can be used to dissolve formation-damaging particles left by the drilling mud or, in carbonate formations, to create flow

passages by dissolving portions of the rock itself

 Hydraulic fracturing involves the high-pressure pumping of fluid into the formation to split the rock apart and increase its flow capacity of tight formations

COMPLETION PROCEDURE

Normally, a completion packer is run and set next , either incorporated into the tubing string or set independently on electric wireline

 The packer is pressure tested to ensure its sealing ability (Many

shallow, low pressure wells, however, do not require a packer to isolate the casing from produced fluids.)

 The tubing must then be "spaced out." ⇒ This requires that a length of tubing be removed from the upper end so that it can be "landed" in the tubing head, which is some distance bellow the rotary table

 Once the tubing has been landed in the tubing head, a temporary plug can be set inside the tubing while the BOP stack is removed and the

surface flow control equipment ("Christmas tree") installed ⇒ This plug

is then removed through the Christmas tree, and the well is completed.

COMPLETION PROCEDURE

 Of course, this procedure will vary according to

 the specific brands of equipment being installed,

 the characteristics of the well,

 and the policies of different companies,

 but the essential sequence of operations will be followed

 One variation is the procedure for perforating, which may be

done after the tubing has been run

⇒ This approach allows the formation to be perforated and

immediately "cleaned up" by allowing it to flow as soon as the perforations are created.

COMPLETION PROCEDURE

The rig will often be moved off location at this point, allowing the well to brought on production On an offshore platform, the rig may be skidded to the next well slot

 If a rod pump is required on the well, it may be installed at this time and the necessary rods and downhole pumping

mechanism run into the tubing

 If gas lift valves have been incorporated into the tubing string, gas may be used to blow the completion fluid out of the tubing and permit the well to flow on its own

In some cases, the well will be "swabbed in" at this point , by running a close-fitting plunger into the tubing on wireline and pulling it back up, thereby displacing the completion fluid in the tubing and allowing the formation to flow

3 PERFORATING

 The use of cemented steel casing to line the wellbore and isolate producing zones is only practical when a method for easily

reopening those zones for production exists

 Jet perforating is the procedure whereby an explosive charge is

used to selectively open passages to the formation through the casing and cement sheath This method:

relies on a conical-shaped charge of explosives to produce a high pressure stream of particles

casing to penetrate casing, cement, and rock

⇒ This technique has pressure, temperature, and penetration

 Jet perforating guns consist of

 a carrier with a series of explosive charges linked together by

a detonating cord

 A variety of gun designs exist; they vary according to :

- the gun is to be run on an electric conductor line or attached

to the bottom of the tubing;

- the gun is to be run through the casing on electric line or tubing, or is to be lowered through the tubing on electric line;

- the gun is retrievable following detonation or is expendable (meaning it is destroyed when the gun is fired);

 Wider, longer perforations require

 larger, stronger jet charges,

 and, larger guns to hold them

 The charge itself is held in a metal case

that is linked to similarly shaped charges by a detonating cord ending in

an electric detonator

 When the gun is fired, an electric

current from the surface sets off the blasting cap detonator , which

When a charge is fired

 The metallic liner collapses to form a stream

of high pressure, high velocity jet particles

 Traveling at 30,000 ft/sec (9100 m/sec), the jet

stream strikes the casing at some 15x10 6 psi (100x 106kPa) a fraction of a second after detonation, to form a perforation.

a) before detonation b) after detonation, showing collapsing liner & swelling casing.

c) volatilizing metal liner and formation of particle

 Retrievable hollow carrier guns have cylindrical steel bodies with closed ports opposite each jet charge

 Fully expendable guns enclose the charges in a frangible aluminum

or ceramic case that disintegrates on firing.

 while semiexpendable guns consist of wire or metal strip carriers that are retrieved after firing

 Through-casing and through-tubing guns of these types differ

primarily

• 3 to 5 inches [7.6 to 12.7 cm] for casing guns,

Type of perforating guns

• Retrievable hollow carrier guns

• Fully expendable guns

PERFORATING GUNS

 Conventional underbalanced perforating is usually carried out

after tubing has been run and equipment is installed to control the sudden pressure surge when the higher pressure formation is opened to the lower pressure wellbore

 For a typical formation the difference between wellbore and

formation pressure may be 300-500 psi (2000-3500 kPa)

 For a low permeability formation, the typical difference between wellbore pressure and formation pressure may be 2000 psi (13,800 kPa) or higher -> the immediate surge of formation fluids to

prevent the clogging of the perforation tunnels with debris

 When a maximum pressure differential is desired, a

tubing-conveyed perforating gun may be used

 it is possible to have the tubing run empty with a ported vent, which opens when the packer is set

 In addition to perforation diameter and length , two important considerations in all types of perforating are

 the shot density

 and phasing of the perforations

 The shot density , or shots per foot, is usually 2, 4, 8,12, or 16 holes in each foot of perforated interval

 Gun phasing can be particularly important when perforating a

fractured well, a highly deviated well, or a multiple completion, where the gun must be oriented to avoid perforating an adjacent tubing string.

 The decision about the interval to be perforated is often made by the

geologist or by the engineer and geologist responsible for the area in which the well is drilled.

 Consideration will be given to maximizing flow rate and minimizing production problems such as produced sand, water coning, or

excessive gas production in an oil well

 The decision is often made after careful review of the log and core data back at the company office

 The geologist's input concerning net pay, sidewall core descriptions, and the areal extent of sand intervals can be crucial in determining the best interval to be perforated.

 One of the advantages of the cased and perforated completion: ability to

MULTI-LAYER PERFORATION

4 Stimulation

 In many cases,

 acidizing

 or fracturing

is a routine part of the completion program

 Either type of stimulation may also be applied soon after a well

 has been completed and

 has tested at lower production rates than expected

 Stimulation may also be part of a remedial or "workover"

program designed to improve productivity following a decline in production