Design Gravel Pack Liner for Deviated Wells

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This article gives an example of completion design with IGP (Internal Gravel Pack) inside a 9 5/8" production casing set through a deviated reservoir (approx. 40 degrees). The most important equipment parts which will be used and the design requirements to the same equipment are presented below.

1 Gravel Pack Base

In cased hole, permanent type gravel pack bases are generally preferred as they provide a reliable fixed platform. Either bridge plugs or sump packers can be used. The advantage of a sump packer is that clean-out trips can be avoided and the possibility for future logging below the pack is maintained.

For the gravel packing of the deviated well a sump packer will be used. The sump packer will be set in a separate run and is not an integrated part of the gravel pack liner. See chapter 5.2 for further details.

 

2 Snap Latch Seal Assembly

The Baker Model 'S-22' Snap Latch Seal Assembly provides a leak proof seal between the packer and the gravel pack liner installation string. It is ideally suited for all applications requiring a snap-in, snap-out indication.

The Snap Latch Seal Assembly is run on the bottom of the gravel pack assembly, and will indicate when the seals are stabbed into the Sump Packer bore.

 

3 Tell Tales

Tell-tales are short (1.5 m-3 m) sections of screen which are included in the liner assembly to assist with gravel placement and/ or give a positive indication over the placement of the gravel.

Lower Tell-Tales

The lower tell-tale assembly consists of a seal bore sub and a short piece of screen located below the main screen. The washpipe is sealed into the sealbore and fluid must enter the washpipe through the tell-tale screen.

Lower tell-tales are frequently used in cased hole gravel packs and are supposed to give a positive indication of when the slurry reaches the bottom of the annulus and to maintain the flow in the screen/ casing annulus, hence promoting good gravel placement.

Slim-pack prepacked screens will be used. See paragraph 4.5.2.4.

 

4 Slim-Pack Prepacked Screen W/ Allpack Shunt System

Allpack System

The Allpack System is a gravel placement/ packing by-pass system that overrides premature bridging effects that occur in thick and non-homogenous formations and results in a higher efficiency placement of gravel pack sand.

It consists of up to four perforated tubes mounted outside the gravel pack screens. These tubes extend 1 or 2 joints up into the blank section. The tubes are mounted to the screen jackets using special adapter rings.

Slot Width and Gravel Size

It is required that the slot width or wire spacing must be smaller than the smallest gravel grain used.

For the  platform wells 16/30 Bakerbond gravel and 0.016" slots will be used for IGPs. The screen width shall be checked both onshore and offshore with a feeler gauge. The following SQAIR tolerance on nominal slot sizes exist:

Nominal Slot Size                                         Tolerance on nominal slot size

                                                                             Max                              Min

0.020"                                                               0.003"                           0.004"

Screen Size

The following considerations apply for the selection of the screen size in IGPs:

-   A minimum radial clearance of one inch (between the largest screen/pipe OD and the casing ID) is        required to allow for washing over the screen.

-   A screen ID larger than the tubing ID offers little advantages.

-   The maximum recommended screen sizes for cased hole completions are given in the table below:

 

Casing Size

(in)

Nominal Screen Size

(in)

7

7 5/8

9 5/8

4

4 1/2

5 1/2

 

Screen Overlap

A minimum screen overlap over the top perforations of 2 metres should be used. A larger overlap provides some flexibility in the screen design as the length can be rounded off to a round number joints. Screen overlap is not a critical consideration and a length of 3 to 6 metres above top perforations is often used.

 

Screen Width and Gravel Size

It is required that the slot width or wire spacing must be smaller than the smallest gravel grain used.

For the horizontal Draugen platform wells 12/20 Bakerbond gravel and 0.020" slots will be used. The screen width shall be checked both onshore and offshore with a feeler gauge. The following tolerance on nominal slot sizes exist:

 

Nominal Slot Size                                    Tolerance on nominal slot size

Max                              Min

0.020"                                                           0.003"                           0.004"

 

Screen Material Selection

The main concern for a screen is to ensure slot integrity over the desired lifetime. 316L alloy has been chosen. This alloy is good for CO2 service (<0.1 bar partial pressure H2S) in producing wells (no free oxygen present) and up to at least 120 degrees Celsius. These austenitic alloys are however susceptible to pitting, crevice, and stress corrosion cracking (SCC) in the presence of chlorides and oxygen. To minimise the risk of corrosion, the pH of the completion/workover brine should be kept above 9. When extended exposure (more than a day) to brine is unavoidable, an oxygen scavenger should be used.

 

Centralisers

For cased hole applications screen centralisation is critical for good gravel placement, especially when there is low clearance between the screen and the casing. Thread-on blade type centralisers for 9 5/8" casing shall be installed on the box end, as positive centralisation is achieved and they are more reliable than clamp-on types.

In addition the joint shall be centralised on the middle.

 

5 4" Seal Bore Receptacle

A 4" Seal Bore Receptacle is placed above the tell tale screens to seal off the return from the gravel pack pumping sequence, forcing the fluids to go through the bottom of the washpipe. This is to ensure that the gravel will be placed all the way down over the screens, leaving no voids in the production zone.

 

6 Blank Pipe

The purpose of the Blank Pipe is to space out between the screens and the Gravel Pack Packer assembly in order to be able to set the Packer at designated depth.

It is also necessary to have Blank Pipe to top off the gravel at a higher than top of the screens. This is to have a reserve of gravel placed so that the compression over time will not result in a poor gravel pack placement.

For deviated wells less than 45 degrees where Waterpack is used, the minimum of Blank Pipe is normally 20 metres. For Gelpack the minimum is normally 10 metres. This is to avoid screenout within the Crossover Tool.

 

7 Shear Out Safety Joint

It is common practice to run a shear out safety joint between the gravel pack assembly and the blank liner to facilitate fishing operations. The shear rating of the safety joint should be sufficient to withstand the loads associated with installation of the pack. 

When installing prepacked screens in horizontal wells a shear out safety joint is not required.

 

8 Knock-Out Isolation Valve

The knock-out isolation valve is a fluid loss control device. It is a flapper valve that is located between the gravel pack extension and the screen and allows isolation of the gravel packed interval once the the job is complete. It is used for wells which experience severe fluid loss.  The use of the knock-out isolation valve will reduce the concerns over losses and allow for a more efficient clean-up of the well bore.

During gravel packing the valve is held open by the washpipe. When the washpipe is pulled the valve closes isolating the formation from wellbore fluids. This valve can subsequently be shattered by applying pressure or with the tail pipe of the production tubing.

9 Gravel Pack Extension With Sliding Sleeve

The Baker model "S" consists of four main components:

1.Upper Extension

This extension provides a space between the gravel pack packer and the sliding sleeve with the gravel pack ports so that the gravel pack crossover tool can be manipulated between the squeeze and upper circulation position while pumping gravel pack sand slurry.

2.Sliding Sleeve

The sliding sleeve consists of two parts, one housing with gravel packing port and one inside sliding sleeve.

The sliding sleeve can be moved and thereby the gravel packing ports closed and opened by running a model "S-1" shifting tool through the sliding sleeve. The shifting tool is placed below the last seal sub of the crossover tool.

The gravel packing port provides communication between the work string and the annulus below the gravel pack packer.

3.Seal Bore Sub

This sub provides the lowest point of two barriers. The upper barrier is the packer and the fluid flow is forced to exit the gravel pack port in the sliding sleeve.

4.Lower Extension

This extension is a housing for the crossover tool and shifting tool that is extended below the seal bore sub.

Due to the need of a "long stroke" crossover tool, the lower extension need to be of certain length to accommodate the lower end of the crossover tool and the "S-1" shifting tool.

 

10 Gravel Pack Packer

A packer is required during gravel packing operations to isolate the treated interval from the wellbore. It is also required when the well is on production to avoid pack fluidisation by upward flow through the annulus and in many cases, to seal the annulus as a mandatory completion requirement.

Permanent tubing retrievable gravel pack packers have been chosen for the  Platform Operations.

When used in a gravel packing context the Baker Model "SC-1L", which will be used for the  Platform Wells, is run and set on a gravel pack crossover tool using a hydraulic setting tool.

The retrieval procedure requires the use of specialised heavy duty retrieval tools run on drill pipe, with drill collars and jars added as necessary. The gravel pack packer is then released by a straight pull. As an alternative it can be retrieved by the use of a packer milling tool.

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