This article gives an example of completion design for a "Slim-pack" prepacked screens, run barefoot in a horizontal 8 1/2" reservoir section. The most important equipment parts and the design requirements are presented below.
1. Double "V"-Set Shoe
The double V-Set Shoe is designed for open hole completions. The design features a one way system for fluids to go through the internal tubing and out at the bottom of the assembly. The Double V-Set Shoe is equipped with double check valves to prevent debris from the well to enter the lower sliding sleeve when RIH.
2. 3 7/8" Seal Bore Receptacle
The 3 7/8" seal bore receptacle shall provide a possibility to seal off the washpipe/ liner annulus when circulating down the washpipe. Sealing is achieved by placing the isolation seal assembly, which is an integrated part of the washpipe, opposite the seal bore receptacle. This makes it possible to circulate down the washpipe, through the 'V'-Set Shoe and into the liner/ open hole annulus without circulating through the screens. At this stage the lower sliding sleeve valve is open and returns are taken via the gravel packing ports with the workstring in the circulating position.
Additionally, once the lower sliding sleeve has been closed, the seal bore receptacle allows the hydrostatic overbalance exerted by the completion fluid to be removed in case losses occur during acidisation.
3. "Slim-pack" Prepacked Screens
Description
The configuration of the openings in all screens is very important. If the slots are parallel, plugging will occur as small particles can bridge inside the slot. Therefore the openings shall have non parallel sides and with the narrowest width on the outside.
Prefaced screens will be used both in the deviated and horizontal wells.
Prefaced screens are basically an assembly of concentric screens packed with gravel. The gravel should always be consolidated to prevent compaction or losing gravel when handling the liner. Strict quality control should be applied to check for voids.
Prepacked screens are more susceptible to plugging during installation because of dirty fluids and damage when handling and running the completion. Therefore ensure that the completion fluid has been circulated/filtered sufficiently before running the prepacked screens.
Screen Size
The nominal screen size for the prepacked screens is 6 5/8".
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 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
The prepacked screens shall be installed without centralisers. This will reduce the friction when running the liner in the horizontal section.
4. 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.
5. 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.
6. 6" Seal Bore Receptacle
The 6" seal bore receptacle shall provide a possibility to seal off the wash pipe/ liner annulus when circulating down the washpipe. Sealing is achieved by placing the locator circulating stinger, which is an integrated part of the washpipe, opposite the seal bore receptacle. Thereby the fluid is forced to move up the liner/ open hole annulus as long as the M.R.C.V. (Multi Reverse Circulating Valve) in the washstring is open and the gravel pack ports is open. See chapter 5.2 for further details.
7. 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.
8. 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.
The gravel pack packer is set hydraulically.
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.