FADE™ is a family of dissolvable alloys and thermoplastic materials that dissolves or degrades when in contact with common wellbore fluid including fresh water, brine, oil-based mud or acid.
Marwell currently offers two main types of material – FADE 100 series comprise metallic alloys and FADE 200 series comprise thermoplastic materials.
FADE™ 100 series is based on a metal alloy common in ball drop applications due to its excellent mechanical strength. Dissolution media is fluid containing chloride (Cl-) such as seawater, brine or even some fresh water. The material will also dissolve in acid.
Applications of FADE
Temporary isolation of the wellbore
Dissolving balls can be used to eliminate the need for wireline runs associated with packer setting. Typically, a seat is installed on tubing below a packer and a dissolvable ball is pumped from surface. Once the ball lands on the seat, the well can be pressurized to activate the packer and test from the annulus. After a pre-determined number of hours or days, the ball will dissolve and pass through the seat and continue to dissolve until the reaction is complete and nothing remains.
The ball outer diameter and the inner diameter of the seat is designed with a minimum overlap depending on required pressure. Typical overlaps are from 0.100” to 0.125”. If required, the seat can be made of cast iron and be milled out at a later stage.
Dissolvable inserts for liner and Inflow Control Devices
Some wells may be planned with inner strings in the reservoir liner to enable placement of fluid in the reservoir section. With temporary plugs in the reservoir liner or directly in Inflow Control Devices (ICD) and Screens, this operation can be carried out without the use of inner strings, which ultimately saves cost and rig time.
Ball activation of sleeves
Frac or stimulation sleeves are activated with balls. The operation starts with pumping the lowest stage first, closest to the shoe, enabling a short section of the reservoir to be stimulated.
Sequentially larger balls are then pumped which isolate the stage below allowing for an efficient stimulation operation without the need for running and pulling plugs between each stage.
Using dissolvable material eliminates the need for producing balls back to surface leaving the wellbore open for future well interventions.
The design process
Designing tools with dissolvable material requires an in depth knowledge of how the degradable material behaves downhole in the well. At Marwell, the design process is based on years of experience with dissolving material and our fit for purpose laboratory set-up which ensures the final design meets the downhole requirement.
At this stage, all the functional requirements including required strength or pressure, geometry and minimum and maximum dissolution time is considered. In addition, the downhole conditions such as temperature and type of fluid exposed to the material at various times is evaluated.
Design & simulation
The mechanical properties of the degradable material are known and a mechanical design is carried out. Unlike normal design engineering, the dissolution time is also included in the design process. The dissolution time is based on previous testing and expressed in Rate of Dissolve, ROD. The ROD unit is mg/mm2/hr which defines weight loss of the material per hour based on how much surface is exposed to the fluid. The ROD varies with temperature, material and type of fluid.
Laboratory qualification testing
This is the heart of the design validation process. Laboratory testing verifies that the final design meets the functional requirements downhole. Testing is carried out with actual or recombined fluid.
Ensuring consistent properties in the final product, every time, the dissolving material is batch or LOT# tested for material properties and dissolve rate.
An operator was looking for a dissolving ball to land on a 3.25″ seat and to hold minimum 8000 psi pressure differential at 70 oC for minimum 8 hours and maximum 14 days.
A simulation was run on FADESim, which is a comprehensive database with dissolve rates of various fluids at downhole temperatures. Based on the simulation, FADE 110 metallic dissolving material was selected as the optimal material, estimating that a ball with 3.375in OD will dissolve to 3.25in in about 19 hours if exposed to 3% NaCl at 70 oC.
The design was further verified through full-scale testing with the ball passing through the seat in 21.5 days, which was in line with pre-estimated results.
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