Light Weight Cement for Structural Casing
10 August 2005
Anyone have comments or opinions about the effectivness of the new
generation of light weight cements for cementing 30" structural
casing on shallow water (+/- 300') floaters. Normal practice is to
use 16 ppg cement and top up if necessary. The claim for the new
generations is that the lighter slurry won't fall away and will set
up at low temperatures while providing acceptable compressive
The North Sea has been on the RHC / X-lite / Lite-fill bandwagon for
a number of years now. There are those of us who are cynical that it
is just a ploy to charge more money. There are numerous issues to
consider - particularly the requirement to separate these cements
from ordinary Class G and this can in itself wreak havoc on the
I would scrutinese the offsets for any prevailing problems as I have
had disappointing results with both 16ppg and 12.5ppg variations.
For structural support we never include the 30" in our calculations
anyway(subsea)so there is no real requirement to fully cement this
and even if you tag or top up it will be very difficult to verify
the effectiveness of the cement bond.
If the normal practice is to use cemoil g at 16ppg and top up why
We used very successfully Dowell's DeepCrete in ultraDW surface
stack wells where getting a TOC to the mudline after fallback was
mission critical. We used a similar blend on a deepwater TLP with
the same issues of requiring high TOC. We used densities as low as
10ppg but more standard at 11.0ppg -12.0ppg. The thickening times
were on the orfer of 12 horus and compressive strength development
was acceptable to a good follow up shoe for kick tolerance. But the
real trick to guaranteeing high TOC's was using huge excess amounts.
We found over time that standard excess percentages were
insufficient and generally went with 300-400% ranges or more usually
whatever cement was on board. We monitored the returns at surface
with the ROV and looked for cement. We also added micah to spacer so
we could see it sparkle under the ROV lights as another trick to see
things at the seafloor. Finally, there has been success using CemNet
(organic fibre) and other agents that prevent fallback. Whether you
could substitute that for excess was not conclusive and I cannot
comment but it would be worth trying.
For further information:
bottomhole static temp: 127F
bottomhole circ temp: 60F
500psi in 10hrs 23 mins
1638psi at 24hrs
I don't think you will have a problem amd Dowell has the experience
although I am sure others do as well.
Just completed a surface casing job with Dowell's Litecrete.
The geologists warned us to expect a weak (depleted) zone at quite
shallow depth. Our plan was to set surface 13.3/8' casing at about
400 m below that zone and the consensus was that standard slurries
of 14.7 Kpa/m lead with 18.6 kpa/m tail would break the weak,
These wells require guaranteed cement to surface due to shallow gas
zones. We had had some lost cement jobs, followed by top up job in
Dowell offered to blend their Litecrete slurry at 13.3 kpa/m. The
job went as planned,cement to surface at 140% excess and no losses.
So everything went as planned. Then they came with the bill at 4
times normal cost, that is is equivalent to a day of rig time !
We are planning 20 of these 20-day wells, so we could drill one more
well if we reverted to Class G standard slurries and concentrate of
the standard slurry recipe for water loss and put in some LCM.
So .. light cement slurries do what is says on the box OK. But you
require a deep pocket.
Meantime .. we are testing bog standard Class G slurry at 13.7 Kpa/m
(litecrete 13.3 Kpa/m) with higher grade water loss and either fiber
or light LCM in the lab now and plan to use it on the next cluster.
I hope that helps
It is now common (if not standard) practice in NEXEN to use light
weight slurries for conductor cementation, whether it be
Halliburton, Dowell or BJ. The compressive strengths develop quickly
(around 900 to 1200 psi in 24 hrs)and the thixotropic nature of the
slurry prevents fallback. On the Buzzard appraisal campaign we were
had many top-ups. When we moved to lightweight slurries the results
were much better. A bit of a challege with these is logistics. As
it's a special blend you need to pay attention to your volumes so
that you are not left with any bulk to return to shore (Unless you
are in a batch situation when you'll use it on the next job).
We took light weight cement down to the Falklands in 1998 for a 6
well program, i.e. offshore semi-submersible campaign in water
depths of 300-1500ft. The light weight slurry decision was made as
prognosed formation strengths could not hold a high wt slurry,
formation break down would occur and top up jobs would inevitably be
needed? Modern light weight cement in set state also provides all
axial and other mechanical support characteristics that a conductor
needs + compressive strengths. ref. 100''s of deepwater cement jobs
conducted world-wide. Experience; The first Falklands well, due
essentially to improper spudding practices (i.e.
rotating/circulating) resulted in a large throated cavern created at
the seabed. Where 5 top up jobs later seabed cement was tagged, more
importantly (topper-uppers' take note!) it took 4 1/2days rig time
to abandon due to the concrete car park on the seabed. ( A genuine
risk where wells have had to be topped up!) Wells 2-6 with modified
spudding practices, we concentrated on objective to drill a 36" and
not a 166inch hole from the seabed. X-lite cementation resulted in
cement to 3ft below seabed, no top ups required and wells cut and
pulled in abandonment without having to negotiate a concrete car
park. Note: Wells all spudded with rotary assemblies and an
inclinometer. Finally if you have to do a top up, the facts are that
your primary cementation 'pressure management' has failed?. This
does not just happen it was caused, where loss should be
investigated and root cause identified e.g. - Poor hole quality -
Formation fracture. - Too high cement slurry wt. - Improper
practices. Causes that can then be determined, evaluated and
remediated against. Action is then to apply a do it once, do it
right design where top up 'accidental loss' will become a thing of
the past event. Only to be retained as an unlikely contingency.
Regards, Peter Aird
Tim, Paladin have used light weight slurries for setting conductors
in these water depths. We use Tuned Lite XL at 12.7 ppg which
acheives a compressive strength of around 1100 psi after 24 hours at
53Â°F. Results so far have been good.
Ops Sup Central/Mature Asset
Tim, We have used light weight cements on quite a number of our
wells in the water depth range +/- 300 ft. We have never had to
perform a top cement job for several years. Typically we use Rapid
Harding Litefill or Rapid Harding with 5% Spherelite. Slurry Density
13.4 ppg. Open Hole Excess 200%. Thickening time 4 hours.
Compressive strength 1300 psi/day. Regards Mike