(See also the Discussion on 'Pumping LCM through a BHA'; http://my-spread.com/discussions/1490
At this week's DWOP we were discussing the use of fibrous material to cure losses and/or assist with hole-cleaning. Whilst discussing the potential to block the BHA (an onshore test is planned), a traditional contingency is to include a circulating sub in the string.
However, a few of the delegates expressed concern about the possibility of the pressure (when the sub is opened by pressurising up on a dropped ball) inducing or worsening losses.
Additional concerns were expressed about the temperature rating of these tools (our sttain BHT is 152°C).
Please could members share with us their experience in this area.
Dave, There are numerous different designs of drill string circulating subs on the market these days that operate in different ways. Some are more sophisticated and hence more expensive as the features and benefits of the designs increase. At the lowest end of the scale is the simple one hit shear pinned ball seat to open ports when a ball lands on the seat, which could produce the issue you described if pinned for a high pressure and the string volume is large. At the other end of the scale are electronically commanded tools that operate by pre-programmed flow rate signals and will open with no pressure in the string at all. There are numerous so called dormant circ subs that won't open until a ball, dart or sleeve is dropped and some of these can be set up to open with a low applied pressure. I suggest the drilling team contacts one of the reputable specialist circ sub suppliers and discusses it with them. There are too many different designs in my opinion to say opening circ subs can induce or worsen losses due to shear open shock.
For sure, blowing a ball seat can surge the hole. More of a problem in smaller hole sizes.
Baker make a DOBS 'delayed opening ball seat' that I have used for 7" and 4-1/2" liners.
The ball is landed and a high activation pressure is held, then bled back to a nominal pressure. The tool cycles over a couple of minutes and you see the nominal pressure drop off when the ball seat is open.
Anyway, DOBS won't help you as you need a tool to run in a drillstring.
If the well is on big losses, you won't be bothered about a pressure surge opening a circ sub. If the losses are not bad and you are worried about surge, spot the LCM thru the bit, but fibrous material may mean you will need to limit product concentration in ppb, but you can always pump move pill volume.
Some back up experience to Scott's answers.
Elf Petroleum Iran used on their development campaigns on Dorood and Balal fields in the Persian Gulf, circulating subs to deal with partial to total losses on almost every well drilled (faults and Karst). Over 3 years and approximately 30 wells drilled, circulating subs proved to be an asset to deal with such losses. The sub was activated upon losses occurrence, losses were not worsening as a result of a potential hydraulic hammer effect on the formations.
Dorood wells highest BHCT temperature was not exceeding 120°C (as far as I remember). But surely there are seals that can manage higher temperatures.
I thought I'd leave this for someone with direct experience, but since nobody has answered so far, here is my penny's worth..
No direct experience as such, but I believe the concern is not justified.
The amount of mud required to pressure up the string is minimal and the additional pressure is dissipated instantly.
A good example of what it would actually look like is an old Dowell Cementing (may they RIP) safety video of a chiksan line weakened to burst at 5,000 psi water pressure. The resulting line failure is a very brief spurt of water, but nothing much. Very different result with 2,000 psi Gas, BTW.
Coming at the problem from a different angle, it used to be common practice to do a 'soft' shut in on a well to 'avoid hydraulically shocking' the formation.
The Roaglands Research institute in Norway did a lot of work actually testing the hydraulic shock effect and essentially found it was in the order of a few PSI (less than 10) at most and was actually less than the pressure drop caused by going through an open choke line (or ECD in a conventional circulating system).
So my thought is basically if you need to open the circ sub due to losses or a blocked BHA, it's not going to exacerbate the problem.
The other way to look at it is, what could you do differently in that situation?
I cannot comment on the temperature rating of the tools - the manufacturer should be able to provide that anyway.
All the Best