Ultra High Performance Composites for Well Integrity and Remediation of Production Wells
NaX® WP Series
The NaX® WP products are designed to provide better integrity than conventional oil well cements, as they have an extremely low porosity and permeability and are non-shrinking which makes them ideal for well barrier applications. The materials also exhibit very good adhesion to steel which is important for zonal isolation where barrier plugs are placed across steel casing or tubing strings.
In addition, NaX® WP products are designed not to invade into a porous formations due to the products’ high cohesiveness (relatively high shear stress) that results in a “self-sealing” property which is important to avoid undue fluid loss and formation damage.
NaX® WP products also have a rheologic behaviour with a relatively high shear stress and low yield point. This is suited to a slower pumping speed, but due to the low yield point the slurry is still very pumpable. The non-thixotropic flow characteristic allows the material to continue flowing after pumping has stopped. This allows the composite material to continue to fill fractures and cavities and provide more effective zonal isolation.
NaX® WP products are all produced at our factory and subjected to internal quality control with testing of key properties performed at our internal oil well laboratory. At well site, NaX® WP products are only mixed with a precise amount of water.
NaX® WP – Product Performance Characteristics
Very good flowability and non-thixotropic behaviour – even small cavities will be filled with slurry, composite material continues to flow even after pumping.
High internal cohesiveness – it does not invade the formation and “self seals”.
Initially high gel strength – illustration of the high cohesiveness of the slurry, mechanism that stops invasion of cement into formation.
Non-porous and highly impermeable – reduces the risk of fluid and gas migration.
Low water demand – a low water-to-cement ratio decreases the porosity and permeability, increasing the “gas tightness”.
Right angle-set – gel-transition period is minimised, avoids channelling and reduces the risk of gas migration.
Shrinkage compensated – average expansion of 0.1 – 0.2% by volume, reduces risk of cracks, channelling or micro-annulus.
Low chloride and other ion penetration – resistant to the saline aquifer waters. Acts as corrosion inhibiting coating.
Zero free fluid – indicative of stable slurry formulation, no separation of solids. Reduces the risk of gas migration.
Very dense cement slurry – high durability. Important for long term P&A applications.
Operational steps for preparing the P&A cement
Very limited preparation is required for preparing the P&A cement on-site and the placement technique as NaX® WP dry products are all premixed and only water has to be added on site. As the only unknown component is the water composition and as water quality can vary from location to location it must be ensured that the mix water is of acceptable quality.
Modelling and simulation
Nautec’s NaX® CPS Modelling and Simulation software is able to be used to predict the surface pump pressures and composite slurry position for any given job design which will include well architecture, fluid and composite slurry properties, pump rates and coiled tubing position.
As the only unknown component is the water composition and as water quality can vary from location to location it must be ensured that the mix water is of acceptable quality.
Once mixed, the NaX® WP composite slurry is transferred into a positive displacement pumping unit. The pump unit is typically connected to a coil tubing unit, or alternatively a work string of jointed pipe. The end of the coiled tubing is placed at the bottom of the well and slowly raised as the slurry is placed in the well.
On site quality control
In order to document the composite plug quality, a QC test program is set up before execution of the work.