Benoil Services Ltd

New Developments - Dual Foil Burst Discs
Dual Foil Burst Disc
Fig: 1 Dual Foil Burst Discs - standard package 11mm-style & 19mm-style
Benoil is pleased to announce a significant development in the field of Burst Discs. In response to customer needs, we have tackled the problem of Burst Disc behaviour in environments of fluctuating pressures.
 
1. The Problem

Oilfield operators and service companies alike will be aware that from time to time there are reports that discs have failed prematurely and at a lower pressure than expected. Many were not aware that their equipment had been subjected to fluctuations of reverse pressures. In many examples however, Benoil was able to show this had been the case; indeed customers were able to prove that discs from the same batch behaved normally when tested; only their operations were causing failures.
 
It became evident to us that many ‘normal’ operations actually encounter severe pressure changes not anticipated, for example, vibration drilling even at presumed positive pressure, or jarring in viscous tars. Others have recognised a potential problem but not had a suitable disc proposition.
 
2. The Solution

All has now changed. The new patented Benoil Twin Disc system offers protection against repeated pressure fluctuations and is now available to customers. It has been thoroughly tested both in the laboratory and in the field and the customers concerned have been delighted by the 100% success.
 
3. Technical Details

As disclosed in Patent Applications:

  •  UK Patent Application GB1406902.5 filed on 16/04/2014
  •  US Patent Application – 14/688,837 filed on 16/04/2015
  •  Canadian Patent Application – CA2,887,915 filed on 16/04/2015

The principle of the new product is the provision of two discs within the same disc assembly. Each disc takes forward pressure within the system, but is protected by its partner disc from reverse pressure. The concept is remarkably simple and effective. It is rather more difficult to achieve in practice, but this has now been done.
 
The problem, in much oilfield practice, is that many discs are fitted in the side wall of the production tool. This gives very little space and is the reason that many standard disc assemblies are only 10mm thick; Benoil nonetheless made even slimmer disc assemblies on request. To fit two discs in the same space so that they have the required interaction has taken much development and testing.
 
The new disc assemblies still burst correctly at the nominated pressure rating. They can still be allowed or adjusted for operation at elevated temperatures. Discs can still have all the variations of thickness, materials, patterns of imprint etc to control the burst behaviour.
 
We do continue to recommend that discs should not be taken to more that 95% of burst value in normal practice. As some clients know, we have previously done testing with them to show the degradation of burst values of standard discs under specific conditions; the new discs eliminate this degradation and one can expect (i.e. we have proved it possible) to cycle a hundred times at say 70% of burst value with no change effect on the disc, quite unlike the standard discs. But the 95% limit still applies because one is using two discs, each with tolerance factors.
 
4. Additional Applications

Such is the consistency of the new Twin Disc that they offer the possibility of application in other areas.
 
  •  They may be used in-line in tools rather than in sidewall applications. It is, of course, not as necessary to condense the disc into such a small thickness in these applications, but the reliability and consistency of operation remains a useful benefit.
 
  •  They might be used in a new in-line isolation technique. This might mean that one could run multiple versions of a tool, or different tools, each separated from the one below by such a disc. If the discs are set of say 500psi intervals, then the top tool is operated first, the string can be re-set and by bursting through the first disc one can operate the second tool. This can be repeated up to the pressure limitations affecting the well, so, for example, 5 operations between 3000psi and 5000psi in one tool run. Given the expense of setting up to run an operation, this could represent a significant cost saving in well development.
 
  •  We envisage one very particular in-line development. We have previously made a tool string sub carrying burst discs in an arrangement designed to replace a conventional double-pump-out sub (based on twin balls). The trigger accuracy was very much improved and more reliable. The Twin Disc will make this even more consistent and simplify the sub; better, it is possible to create nearly full or even full throat. Sometimes, this does not matter, but it opens up the possibility of running tools through.
 
  •  There has, in recent years, been much interest in completion strings with separators; most of the work revolved around glass separators which, when shattered in controlled fashion, would in theory leave little residue and a clean fill bore. This permits entry of subsequent intervention strings at full bore. There has been some success, but the system has disadvantage in requiring an explosion to shatter the glass; nor does the glass always shatter fully; and in non-vertical wells the glass does not always fall out of the way. Use of a Twin Disc would be an alternative, particularly if engineered to open flat to the walls.
 
  •  There are specialised tools devised by customers, for which we have supplied discs in special forms to act as triggers. We expect the Twin Disc to give improved performance in this area and other devices can be envisaged.
 
  •  There are non-oilfield applications where sudden pressure changes are or might be encountered. These include civil uses such as chemical plants, refineries, nuclear plants, aircraft and military applications.
 
Reliability of not failing prematurely due to fluctuations of pressure but of working as required when required is essential in all such uses. Benoil is now expanding and ready to work with clients accordingly.

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